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Environmental Microbiology, 2025; 27:e70033
https://doi.org/10.1111/1462-2920.70033
ENVIRONMENTAL MICROBIOLOGY
Environmental Microbiology
BRIEF REPORT
New Strains of the Deep Branching Streptophyte
Streptofilum: Phylogenetic Position, Cell Biological and
Ecophysiological Traits, and Description of Streptofilum
arcticum sp. nov
KarinGlaser1 | TatianaMikhailyuk2 | CharlottePermann3 | AndreasHolzinger3 | UlfKarsten4,5
1Institute of Biological Sciences, Biology/Ecology, Technical University Bergakademie Freiberg, Freiberg, Germany | 2M.G. Kholodny Institute of Botany,
National Academy of Sciences of Ukraine, Kyiv, Ukraine | 3Department of Botany, University of Innsbruck, Innsbruck, Austria | 4Institute for Biological
Sciences, Applied Ecology and Phycology, University Rostock, Rostock, Germany | 5Interdisciplinary Faculty, Department of Maritime Systems, University
of Rostock, Rostock, Germany
Correspondence: Karin Glaser (karin.glaser@ioez.tu-freiberg.de)
Received: 10 July 2024 | Revised: 16 October 2024 | Accepted: 20 December 2024
Funding: This work was supported by Deutsche Forschungsgemeinschaft (KA899/33- 1), Austrian Science Fund (10.55776/P34181), and Georg- Forster
research fellowship from the Alexander von Humboldt Foundation (871072).
Keywords: cell coverage| desiccation| ecophysiology| ITS2 secondar y structure| PI- curve| rbcL phylogeny| SSU rRNA| Streptofilum| TEM| temperature
ABSTRACT
Streptofilum capillatum was recently described and immediately caught scientific attention, because it forms a phylogenetically
deep branch in the streptophytes and is characterised by a unique cell coverage composed of piliform scales. Its phylogenetic
position and taxonomic rank are still controversial discussed. In the present study, we isolated further strains of Streptofilum
from biocrusts in sand dunes and Arctic tundra soil. Molecular and morphological characterisation including transmission
electron microscopy confirmed that both new strains belong to Streptofilum. The Arctic strain is described as a new species,
Streptofilum arcticum sp. nov., based on molecular differences, a specific sarcinoid morphology and unique ultrastructure with
massive cell coverage composed of pili- shaped scales. A comprehensive characterisation of the ecophysiological traits of both
new Streptofilum isolates and the original one revealed a broad temperature tolerance, a rapid recovery of photosynthetic perfor-
mance after desiccation, an efficient photosynthesis at low light and a tolerance to high- light conditions. In addition, Streptofilum
could cope with UV irradiation, but only S. capillatum grew under UV exposure. All Streptofilum strains are well- adapted to
water- deprived terrestrial habitats such as biocrusts. From this study it can be concluded that already early- branching strepto-
phytes were able to tolerate terrestrial conditions.
1 | Introduction
Streptophyte green algae contain the closest living relatives
of land plants and thus, have been in research focus for de-
cades as living fossils in the evolutionary process of terrestri-
alization. A number of fundamental innovations enabled land
plants to colonise terrestrial ecosystems, for example, complex
cell walls, roots and stomata. However, molecular evidence
indicate that streptophyte algae already had key adaptations to
terrestrial life long before vascular plants developed (Harholt,
Moestrup, and Ulvskov 2016; De Vries and Archibald 2018;
Dadras et al. 2023). Multicellularity emerged already in the
Klebsormidiophyceae (Bierenbroodspot et al. 2024), and we
only start to understand the diversity of the steptophytes
most distant to land plants (Irisarri etal.2021). Streptophyte
green algae comprises many aero- terrestrial taxa with various
© 2025 Joh n Wiley & Sons Ltd.
2 of 15 Environmental Microbiology, 2025
adaptive traits to survive outside aquatic habitats, such as a
self- protective filamentous lifestyle, excretion of mucilage
sheds, accumulation of UV- sunscreen compounds and poten-
tially flexible cell walls to prevent plasmolysis during desic-
cation events (Holzinger and Karsten 2013; Herburger and
Holzinger2015; Hartmann etal.2020).
A new streptophyte genus was discovered just few years ago,
Streptofilum which exhibited two unique characteristics and
thus caught broad attention (Mikhailyuk et al. 2018): first,
although the phylogenetic position of this alga could not be
clearly solved, it seemed to be a deep- branching streptophyte.
Second, Streptofilum is characterised by a unique cell cover-
age with pili- shaped scales, and at the TEM level distinct from
the scales of Mesostigma or Chlorok ybus zoospores. Those two
algal genera are basal streptophytes representing the earliest
branches of the phylogenetic tree of streptophyte alga. Other
basal streptophytes, like Klebsormidium and vegetative cells
of Chlorokybus, develop a cellulose cell wall, similar to the
primary cell wall of plants. In sharp contrast, a cell coverage
composed of pili- shaped struct ures as observed in Streptofilum
was never described before.
Recent publications used more complex molecular data and gave
an improved insight in the phylogenetic position of Streptofilum
(Mikhailyuk et al.2018). One study sequenced the chloroplast
genomes of American isolates of Streptofilum and several basal
streptophytes (Glass et al. 2023). The authors confirmed the
first conclusions (Mikhailyuk etal.2018) that Streptofilum rep-
resents indeed a deep branch close to the most ancestral strep-
tophyte classes Mesostigmatapyhceae and Chlorokybophyceae
and might even be assigned to an own class. Another publica-
tion sequenced the transcriptome of the original Streptofilum
isolate and several strains from Klebsormidiophyceae. Contrary
to previous publications, the published phylogenetic tree showed
Streptofilum within the Klebsormidiophyceae (Bierenbroodspot
etal.2024). A new manuscript, which is not yet peer- reviewed,
evaluated the molecula r data of Bierenbroodspot etal.(2024) and
indicated contamination in the transcriptome of Streptofilum,
which could explain the contrasting results on the phylogenetic
position of this genus (Žárský and Eliáš2024). The preliminary
phylogenetic results after removing the potential contaminating
sequences are in line with Glass et al.(2023) and Mikhailyuk
et al. (2018) indicating that Streptofilum represents indeed a
deep branch among the early- diverged streptophytes. The on-
going controversial debate clearly points out that there are still
uncertainties about the phylogenetic position of Streptofilum.
Therefore, more research with additional strains are urgently
needed to establish a stable phylogenetic positioning of this
unique genus.
Recently, two new strains of Streptofilum were isolated in bi-
ocrusts from deserts in the United States (Glass et al. 2023).
Biocrusts can be regarded as a microecosystem with microalgae
as primary producers and drivers of biogeochemical activities.
As a consequence of microbial activity, biocrust microecosys-
tems can create microclimatic conditions and steep physico-
chemical gradients, which might be less harsh compared to bare
soil. For example, the water retention is changed by biocrusts
compared to bare soil due to the excretion of extracellular poly-
meric substances (Chamiz o etal.2016; Geraldes a nd Pinto2021).
The microclimatic conditions in the biocrusts foster unique mi-
crobial assemblages (Glaser etal.2022). Such moderate micro-
climatic conditions probably allow various algal taxa to thrive,
which might be otherwise rare and less abundant in bare soil,
like Streptofilum. A previous publication described the original
Streptofilum strain as adapted to low- light and less desiccation
tolerant compared to other basal streptophytes (Pierangelini
etal.2019).
For this study, we isolated two new Streptofilum strains from bi-
ocrusts inhabiting coastal sand dunes of the Baltic Sea and polar
tundra soils at Spitsbergen. Based on these locations, which dif-
fer in their environmental conditions, we hypothesized that the
genus Streptofilum has the ecophysiological potential to occur
in a wide range of habitats from hot and cold deserts to mesic
regions. A wide biogeographic distribution would generally
require euryoecius adaptive traits, which were experimentally
evaluated. We expected that the Artic strain is characterised by
a lower optimum growth temperature and higher desiccation
tolerance than the strains from temperate regions because of
the colder and drier environment in polar regions. Further, we
investigated the phylogenetic position by rbcL phylogeny, SSU
rRNA and ITS2 secondary structure and hypothesized that the
unique cell coverage is a common cell biological feature among
members of Streptofilum.
2 | Material and Methods
2.1 | Habitats and Culture Conditions
The original Streptofilum strain SAG 2559 was isolated from ar-
able sandy soil in Czech Republic (Mikhailyuk etal.2018). The
new strain Hg- 2- 4 was isolated from a biocrust in coastal sand
dunes of the Baltic Sea (Heiligendamm, Germany), details on
sampling location were published earlier (Khanipour Roshan
et al. 2020). The other new strain O3- 3A- 2 was isolated from
a biocrust collected from tundra soil in Spitsbergen, details on
sampling location published elsewhere (Kern etal.2019).
Isolation, purification and establishment of clonal cultures fol-
lowed the procedure according to Samolov etal.(2020). The cul-
tures were grown in 3 N BBM medium (Starr and Zeikus1993) at
20°C under low light conditions (~50 μmol photons m−2 s−1) and a
16:8 h light:dark cycle. Before each experiment, the strains were
acclimated to the experimental conditions at least 4 days in ad-
vance. The strains were deposited in IBASU- A, M.G. Kholodny
Institute of Botany of NA SU of Ukraine, Kyiv, Ukraine under ac-
cession numbers IBASU- A- 780 and IBASU- A- 781 and are kept
as duplicates under the original strain numbers at the University
of Rostock.
2.2 | Light Microscopy
Morphological examinations of both clonal strains were per-
formed at different culture age: 3 weeks, 1–2 months and 1 year
with Olympus BX51 and BX53 light microscopes (Olympus,
Tokyo, Japan), Nomarski differential interference contrast (DIC)
optics and ×40 and ×100 objective lenses. Photomicrographs
were taken with digital cameras Olympus UC30 and LC30
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(Olympus, Tokyo, Japan). The mucilage cover of the cells was
stained with 1% methylene blue. The dimensions of 30 cells were
measured; results are given as a range of average value (standard
deviation) and in addition the minimum and maximum values
in parenthesis.
2.3 | Histological Observations and Transmission
Electron Microscopy (TEM)
For TEM samples were either chemically fixed or high pres-
sure frozen (HPF) followed by freeze substitution (FS) accord-
ing to published protocols (Aichinger and Lütz- Meindl2005;
Holzinger, Roleda, and Lütz 2009). Samples were either em-
bedded in Agar Low viscosity resin kit (Agar Scientific, Essex,
UK) or modified Spurr's resin (Mikhailyuk et al. 2018). For
histological observations, semithin sections (~0.6 μm) were
prepared with a Reichert Ultracut (Leica Microsystems,
Wien, Austria) and 0.3% Toluidine blue stained sections were
viewed at a Zeiss Axiovert 200 M light microscope (Zeiss,
Jena, Germany). For TEM, ultrathin sections (~60 nm) were
prepared and counterstained with 2% uranyl acetate and
Reynold's lead citrate. TEM micrographs were taken on a
Zeiss Libra 120 TEM (Carl Zeiss AG, Oberkochen Germany)
at 80 kV, equipped with a TRS 2 k SSCCD camera and oper-
ated by ImageSP software (Albert Tröndle Restlichtverstärker
Systeme, Moorenweis, Germany).
2.4 | DNA Isolation, Phylogeny and Secondary
Structure
Genomic DNA was extracted using the NucleoSpin Plant II
mini kit (Macherey Nagel, Düren, Germany). Amplification
of SSU rRNA including ITS region and rbcL genes followed
previously published protocols including calculation of rbcL
phylogenetic tree (Mikhailyuk et al. 2018). Phylogenetic trees
were constructed in the program MrBayes 3.2.2 (Ronquist and
Huelsenbe ck 2003), using an evolutionary model GTR + G + I,
with 5,000,000 generations. Two of the four runs of the Markov
chain Monte Carlo were made simultaneously, with the trees
taken every 500 generations. Split frequencies between runs
at the end of the calculations were below 0.01. The trees se-
lected before the likelihood rate reached saturation were subse-
quently rejected. The reliability of tree topology was verified by
maximum- likelihood (ML) analysis, using the program GARLI
2.0, and the bootstrap support was calculated with 1000 repli-
cates. The rbcL tree is presented as Figure5, the SSU phyloge-
netic tree is presented in Figure S3.
To construct secondary structures of ITS2, the ITS2 se-
quence was compared with published sequences and second-
ary structures of other streptophyte algae: Klebsormidium
(Glaser etal.2017; Samolov etal.2019), Hormidiella parvula,
Streptosarcina arenaria (Mikhailyuk etal.2018), Chlorokybus
atmophyticus (Irisarri et al. 2021), Interfilum paradoxum,
Entransia fimbriata, Spirotaenia condensata and Mesostigma
viride. The secondary structures of ITS2 of the last four rep-
resentatives were built de novo using published sequences
(Mikhailyuk etal.2008; Sluiman, Guihal, and Mudimu2008;
Cheng et al. 2019). Helices were folded with the online
software mfold (Zuker2003) and visualised in the online tool
Pseudoviewer (Byun and Han2009).
2.5 | Desiccation Experiment
The experiment followed the procedure published earlier
(Karsten, Herburger, and Holzinger2016) with following varia-
tion: 100 mL LiCl solution (40% w/v) was filled in each chamber
to achieve desiccating conditions in the air- tight chamber, which
resulted in stable relative humidity (RH) of around 47% (MSR
145 W; MSR Electronics GmbH, Switzerland). Streptofilum bio-
mass was transferred onto a glass fibre filters, and positioned
in the desiccation chamber (four replicates). The yield of pho-
tosystem II (YII) was measured as a proxy for the vitality of
the cells using non- invasive pulse amplitude modulation fluo-
rometry (PAM2500, Walz, Germany). The signal was recorded
during the desiccation process every 30 min for up to 4.5 h. After
YII signals completely declined, the filters were rewetted with
250 μL medium (3 N BBM, see culture conditions), transferred
to a chamber filled with 100 mL water (RH ~95%) and recovery
was monitored. YII was recorded every 5–10 min for 1.5 h and
additionally after 24 h.
2.6 | Photosynthesis- Irradiance (PI) Curves
PI curves of the three Streptofilum strains (four replicates per
strain) were measured according to the protocol published ear-
lier (Prelle etal.2019). Briefly, ~3 mL of thin log phase algal sus-
pension of each strain and 2 mM final concentrationof NaHCO3
were added to four airtight water- tempered (20°C) oxygen elec-
trode chambers (DW1, Hansatech Instruments, King's Lynn,
UK). The oxygen concentration was measured at 10 increas-
ing photon flux density levels ranging from 0 to ~1.500 μmol
photons m−2 s−1 of photosynthetically active radiation (PAR),
using a non- invasive oxygen dipping probe (DP sensors PreSens
Precision Sensing GmbH, Regensburg, Germany). Chlorophyll
a (Chl a) was extracted after the experiment (using 96% etha-
nol at 70°C for 10 min) and quantified spectrophotometrically
(Ritchie2006).
2.7 | Temperature- Dependent Oxygen Production
and Consumption
The photosynthetic and respiratory responses of each
Streptofilum strain (n = 4) at temperatures between 5°C and
40°C were measured using the same oxygen optode system as
for the PI curves. After 20 min incubation in the dark, the respi-
ratory oxygen consumption (10 min in the dark), followed by the
photosynthetic oxygen production (10 min under light- saturated
conditions at 335 μmol photons m−2 s−1 PAR) were determined.
Measurements were normalised to the Chl a concentration (see
procedure above).
2.8 | Growth Rate Under UV Exposure
The fluorescence of Chl a was used as a proxy for biomass to
calculate the temperature- dependent growth rates of the three
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4 of 15 Environmental Microbiology, 2025
Streptofilum strains. The in vivo Chl a fluorescence measure-
ments were performed according to the previously published
protocol (Karsten, Klimant, and Holst 1996). The cultures
were grown in disposable plastic Petri dishes, kept at constant
temperature of 20°C, and measured every 24 h for 4 days. In
addition to PAR, UV emitting light bulbs were used. The Petri
dishes were covered with two different foils: one foil allowed
the UV radiation to pass, the second foil absorbed light below
400 nm (control) (Kitzing, Pröschold, and Karsten 2014). The
UV- treatment was undertaken in triplicates. Both treatments
were exposed to 80–90 μmol photons m−2 s−1 (Lumilux Deluxe
Daylight L15W/950; OSRAM), the UV- treated cells were addi-
tionally exposed to 6–7 W m−2 s−1 UV- A and 0.37–0.45 W m−2 s−1
UV- B (Q- Panel- UVA 340 fluorescent lamps, Cleveland, USA).
2.9 | Statistical Analyses
All statistical analyses were done in R, version 4.2.1
(R Development Core Team 2022) or Microsoft Excel.
Photosynthetic irradiance (PI) curves were fitted using
the Walsby model in Excel, based on least- square method
(Walsby 1997). Based on this model, maximum rates of net
primary production (NPPmax), respiration (R), light utilisation
coefficient (α), photoinhibition coefficient (β), light saturation
point (Ik), and the light compensation point (Ic) were calcu-
lated. Temperature curves were fitted in R using the model
published by Yan and Hunt, also based on the least- square
method (Yan and Hunt1999). Confidence intervals for max-
imum oxygen production, optimum and maximum tempera-
tures were calculated using the command ‘confint2’ (package
nlstools).
3 | Results
3.1 | Morphological Characterisation of Two New
Streptofilum Strains
Strain Hg- 2- 4 (IBASU- A- 780) was morphologically similar to
the authentic Streptofilum capillatum (SAG 2559, IBASU- A- 521,
Figure 1A–C). Cells were grouped in short filamentous- like
structures, often disintegrated to diads and unicells, and sur-
rounded by homogenous mucilage with waved or lobbed edge
(Figure1D–G). Hg- 2- 4 formed smooth colonies on the agar sur-
face. Vegetative cells were ell ipsoid to ovoid, (6.1)7.0–8.8(12.1) μm
length, and (4.6)5.0–5.8 μm width. Chloroplast was parietal,
plate- shaped with smooth margin and single pyrenoid sur-
rounded by several starch grains. Vegetative reproduction of
Hg- 2- 4 occurred by cell division in one plane (sporulation- like
type) with formation of cell diads. Sexual reproduction was not
observed. This strain differed from SAG 2559 by slightly longer
cells. Both strains were isolated from rather sandy substrates of
similar geographical region (Western Europe: Czech Republic
and Germany).
Strain O3- 3A- 2 (IBASU- A- 781) was characterised by a differ-
ent morphology. It had a sarcinoid thallus, forming 2–4 celled
packet- like and rarely short f ilamentous- like aggregations, often
disintegrated to diads and unicells (Figures1H–K and 2A). Cells
were surrounded by thick (to 5.0–10.0 μm) layered mucilage
with waved edge. Mucilaginous caps on cells and layered finely
structured mucilage were especially prominent in old cultures
(Figure 2E,F). This alga formed large mucilaginous colonies
which resemble Radiococcaceae- like morphology (Figure 2G).
Due to the similar cell morphology (see below) it also resembled
a Chlorokybus- like morphology, but with much smaller cells.
O3- 3A- 2 formed cluster- like mucilaginous colonies on the agar
surface. Vegetative cells were widely ellipsoid to almost spheri-
cal, (5.1)6.4–7.6(11.0) μm in length, and (4.2)–5.5–6.9(8.6) μm in
width. Chloroplasts were parietal, plate- shaped, with a smooth
or waved margin and a single pyrenoid surrounded by several
starch grains. Vegetative reproduction occurred by cell division
in several planes (sporulation- like type) and formation of spo-
rangia with 2–4 (8) cells (Figure2B–D). Due to widening of the
sporangial cell wall the adult cells were organised in 2–4 celled
groups and formed large mucilaginous colonies. Sexual repro-
duction was not observed. T he strain O3- 3A- 2 differed from SAG
2559 by general sarcinoid and packet- like morphology, much
thicker and layered structured mucilage as well as a different
shape of the cells. Because of more rounded cells of the strain
O3- 3A- 2 cell division took place in several planes that leading to
cell packet formation. Strong mucilage prevented disintegration
of cell packets after division and promoted the general sarcinoid
morphology of this alga.
3.2 | Ultrastructural Characterisation
of Streptofilum Shows Unique Cell Coverage With
Pili- Shaped Scales
When investigated by TEM after high pressure freeze fixation,
S. capillatum SAG 2559 (Figure3A–D), exhibited a cell coverage
composed of characteristic electron dense piliform scales. These
scales were densely arranged close to the plasma membrane and
forming a looser arrangement outside, sometimes forming a
cap- like region (Figure3A). The cells contained a nucleus with a
distinct nucleolus, one chloroplast with starch grains, mitochon-
dria, numerous membrane- surrounded bodies up to 500 nm in
diameter with a granular medium electron dense content and
Golgi bodies (Figure 3A). The Golgi bodies formed vesicles
containing individual scales (Figure 3B–D), the vesicles were
detached at the trans- side of the Golgi body (Figure 3C), and
several vesicles with scales were found close to the plasma mem-
brane (Figure3D). In high pressure frozen Streptofilum strain
Hg- 2- 4 a similar arrangement of the cell coverage was observed
(Figure3E–J). In cross- sections, the parietal arrangement of the
chloroplast was visible (Figure 3E). One peroxisome was ob-
served between the nucleus and the chloroplast that contained
numerous starch grains and plastoglobules (Figure3E,F). The
membrane- surrounded bodies with granular contents were elec-
tron denser (Figure3E–I) as in S. capillatum SAG 2559. During
cell division newly formed cross wal ls contained a loose arrange -
ment of scales (Figure 3H,I), microtubles were visible perpen-
dicular to the cross walls (Figure3H). Particularly in the area of
the newly formed cross walls many vesicles containing individ-
ual scales were observed in the cytoplasm (Figure3I). When the
scale containing vesicles were longitudinally sectioned, scale
lengths of up to ~500 nm were observed (Figure3J).
The ultrastr ucture of strain O3- 3A- 2 (Figure4) was distinct from
both S. capillatum strains (see above). Toluidine blue stained
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5 of 15
semi- thin sections of chemically fixed material showed sarci-
noid cell packets with a massive multilayered cell coverage with
a diameter of up to ~5 μm (Figure4A,B). When viewed by TEM
(Figure 4C–H), the cytoplasm had a dense appearance with
clearly visible thylakoid membranes in the chloroplast and the
pyrenoid was surrounded by starch grains (Figure4C,D). The
piliform scale arrangement of the cell coverage was denser close
to the plasma membrane, and looser in more distant position
(Figure 4C,D). At the junction of two cells, the piliform scales
appeared denser (Figure4E). Tangential sections showed a net-
like arrangement of the scales (Figure 4F). The multi- layered
arrangement of the scales is illustrated in Figure4G, where the
outermost layer was again much denser when compared to the
inner layers. In a close- up the scales appeared to change orien-
tation from net like to parallel depending on the plain of section
(Figure4H).
FIGUR E | Micrographs of Streptof ilum strains: General v iew of filaments or packets surrounded by mucilage envelope (A, B, D, E, H, and I) and
staining of mucilage with Methylene blue (C, F, G, J, and K); (A–C) Streptofilum capillatum SAG 2559, (D–G) Streptofilum capillatum Hg- 2- 4, (H–K)
Streptofilum arcticum sp. nov. O3- 3A- 2. Scale bars: 10 μm.
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6 of 15 Environmental Microbiology, 2025
3.3 | Molecular Phylogeny and ITS2 Secondary
Structure of Streptofilum
The SSU rRNA sequences of the strains SAG 2559 and Hg-
2- 4 were nearly identical (99.9% identical), similarity of SAG
2559 to O3- 3A- 2 was lower (99.2%, Table1). Additionally, the
partial rbcL sequence of SAG 2559 and Hg- 2- 4 were nearly
identical (99.8%), but differed to the sequences of O3- 3A- 2
(97.7% identical to SAG 2559). The rbcL phylogenetic tree
showed all three plus two American Streptofilum strains close
to each other (Figure 5). The authentic S. capillatum strain
SAG2559 is very closely positioned to the two American
strains (ZNP2- V and BC4- VF) and our new strain from the
German coastal dunes (Hg- 2- 4). The Arctic strain O3- 3- 2A
was found to be located within the Streptofilum clade, but sep-
arate from the other strains. The lineage Streptofilum fell out-
side of the Klebsormidiophyceae and close to early- branching
Streptophytes.
The ITS2 region of Streptofilum strain O3- 3- 2A differed largely
from all published sequences: a direct sequence comparison
did not result in any hit in the GenBank database. Thus, the
secondary structure of the ITS2 region was used for further
comparison. The ITS2 secondary structure of the Streptofilum
strain O3- 3A- 2 was character ised by three helices, of which the
third was branched (Figure 6). The first and also the second
helix of Streptofilum O3- 3A- 2 showed similar characteristic
features like other streptophyte and also chlorophyte algae.
For example, the pyrimidine–pyrimidine- mismatch in the
second helix is common for all eukaryotes (Caisová, Marin,
and Melkonian 2013). Mesostigma and Spirotaenia have
also a branched third helix; but in those two genera a fourth
helix is present (Figure S1). Chlorokybus is characterised
by three helices, but without branches (Irisarri et al.2021).
Representatives of Klebsormidiophyceae (Klebsormidium,
Interfilum, Hormidiella, Streptosarcina and Entransia) were
characterised by completely different secondary structure of
ITS2 (Figure S2). Their ITS2 was quite uniform in all gen-
era with four helices without branches (Glaser et al. 2 017;
Mikhailyuk etal.2018; Samolov etal.2019).
3.4 | Streptofilum Exhibits Desiccation Tolerance
The Arctic strain O3- 3- 2A showed no photosynthetic activity
after ~110 min of controlled desiccation (at 47% RH), whereas
the other two strains sustained around 1 h longer under these
conditions (Figure7A). The kinetics of recovery after rewetting
the filters and transferring them to 95% RH was similar for all
three strains: directly after rewetting nearly 100% of the initial
value was reached, which decreased to ~80% of the initial value
after 24 h (Figure7B).
FIGUR E | Streptofilum arcticum sp. nov. O3- 3A- 2: Cell packet and aggregations surrounded by mucilage (A); reproduction by cell division on
2–4 and 8 daughter cells (B–D); thick layered and finely structured mucilage in old cultures (E, F); general view Radiococcaceae- like colony with
grouped cells surrounded by common mucilage (G); staining of mucilage with Methylene blue (E–G). Scale bars: 10 μm.
14622920, 2025, 1, Downloaded from https://enviromicro-journals.onlinelibrary.wiley.com/doi/10.1111/1462-2920.70033 by Andreas Holzinger - Readcube (Labtiva Inc.) , Wiley Online Library on [08/01/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
7 of 15
3.5 | Streptofilum Reveals Low Light Compensation
and no Photoinhibition at High Light
The kinetics of the PI curves was found similar in all three
Streptofilum strains (Figure 8A–C). No photoinhibition
was detected and the light- compensation point was already
reached below ~5 μmol photons m−2 s−1 (Table2). Respiration
rate, alpha and light saturation point were similar in all iso-
lates (Table2). In contrast, the maximum photosynthetic ox-
ygen production was different among the strains: SAG 2559
had the lowest net oxygen production of ~78 μmol O2 mg−1 Chl
a h−1 and Hg- 2- 4 the highest oxygen production of ~127 μmol
O2 mg−1 Chl a h−1.
3.6 | Temperature Dependent Photosynthesis
and Respiration
All three strains exhibited a broad temperature tolerance be-
tween 5°C and 40°C following classical Gauss- dynamics
FIGUR E | Transmission electron micrographs of Streptof ilum capillatum SAG 2559 (A–D) and Hg- 2- 4 (E–J) fixed by high pressure freeze fix-
ation. An overview showing cell coverage composed of densely arranged piliform scales close to the plasma membrane and a cap- area with looser
arranged scales, chloroplast with starch grains, membrane- surrounded bodies with granular content (asterisks) and Golgi bodies, (B) detail with
nucleus and nucleolus, Golgi body w ith several vesicles containing scales (arrows), (C) detail with G olgi body and vesicles containing scales detached
from the trans- side. (D) numerous vesicles containing scales (arrows) close to the plasma membrane, (E) overview of cross section with nucleus,
chloroplast and peroxisome, membrane surrounded- bodies with granular content appear electron dense (asterisk), (F) longitudinal section with pa-
rietal chloropla st surrounding the nucleus, one peroxisome, mitochondria , (G) detail view of the cell coverage, scales a rranged denser close to plasma
membrane, scales more scatted in the mucilage at the outside, (H) longitudinal section during cell division with loosely arranged scales in the newly
formed cross wall, microtubules perpendicular to cross wall, (I) detail v iew of newly formed cross wall, numerous vesicles containing scales (arrows)
close to the plasma membra ne, (J) longitud inal section of vesicles contai ning scales (arrows). CC, cell c overage; Ch, chloroplast; G, G olgi bo dy; M, mi-
tochondrion; MT, microtubules; N, nucleus; Nu, nucleolus; P, peroxisome; PG, plastoglobuli; S, starch grain; Sc, scale. Asterisks indicate membrane-
surrounded bodies with granular content, arrows indicate vesicles containing scales. Scale bars: A, E: 1 μm, B, F, G, H: 500 nm; C, D, I, J: 250 nm.
14622920, 2025, 1, Downloaded from https://enviromicro-journals.onlinelibrary.wiley.com/doi/10.1111/1462-2920.70033 by Andreas Holzinger - Readcube (Labtiva Inc.) , Wiley Online Library on [08/01/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
8 of 15 Environmental Microbiology, 2025
(Figure8D–F and Table3). The optimum temperature for pho-
tosynthesis was with ~26°C similar for all three strains, as well
as the maximum temperature with ~44°C. The tolerance width
for optimum photosynthesis (80% of maximum capacity) was
broad, ranging from around 15°C to 35°C (Figure S4). The opti-
mum respiration was measured at 34°C–37°C, which is higher
than the respective photosynthesis.
3.7 | Differential UV- Tolerance in the Investigated
Streptofilum Strains
The Streptofilum strains SAG 2559 and Hg- 2- 4 were tolerant
to UV treatment as reflected by similar growth rates with and
without UV radiation (0.25–0.3 μ day−1). In contrast, the Arctic
strain O3- 3- 2A surprisingly did not grow under UV radiation. It
is worth to mention, that the measured Chl a signal remained
unchanged over the experiment course (4 days) and the biomass
still appeared green after the experiment.
4 | Discussion
In the present study, a comprehensive characterisation of two
newly isolated Streptofilum strains in comparison to the au-
thentic S. capillatum strain (Mikhailyuk etal. 2018) was per-
formed. While strain Hg- 2- 4 was morphologically very similar,
strain O3- 3A- 2 exhibited morphological and some physiological
differences. After the first record of S. capillatum SAG 2559
FIGUR E | Histological and ultrastructural characterisation of the newly described Streptofilum arcticum sp. nov. (O3- 3A- 2). (A, B) Toluidine
blue stained semi- thin sections showing massive multi- layered cell coverage, (C) cell overview with chloroplast and pyrenoid surrounded by starch
grains, cell covera ge multilayered, (D) starch grai ns in chloroplast, arra ngement of the sca les in the c ell coverage is denser (arrow) close to the pla sma
membrane, multilayered and looser distant from the cytoplasm, (E) connection zone between two cells, (F) tangential surface section showing the
net- like arrangement of the scales in the center (asterisk), and wave like at the surface (arrow), (G) cross section through multi- layered cell coverage,
arrangement of scales with different densities, note the very dense arrangement at the outer surface (arrow), (H) close- up of scales with changing
orientation from net- like (asterisk) to parallel (arrows). CC, cell coverage; Ch, chloroplast; S, starch grain. Scale bars: A, B: 20 μm; C–F, 1 μm; G, H:
500 nm .
TABLE | Sequence identity of three Streptofilum strains; upper
right the identity of 18S rRNA sequences (bold), down left of rbcL
sequences (italic).
SAG 2559 Hg- 2- 4 O3- 3A- 2
SAG 2559 0.999 0.992
HG- 2- 4 0.998 0.993
O3- 3A- 2 0.977 0.978
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9 of 15
(Mikhailyuk et al. 2018), more Streptofilum strains were iso-
lated from biocrusts: two strains from (semi- )arid regions in the
United States (Glass et al.2023) and two strains presented in
this study from mesic and Arctic regions. One of the new strains
(Hg- 2- 4) was morphologically similar to the authentic strain of
S. capillatum with very small differences (slightly longer and
wider cells of Hg- 2- 4 [average size 7.0–8.8 × 5.0–5.8 μm oppo-
site 5.7–6.7 × 4.6–5.0 μm in SAG 2559]). In contrast, the Arctic
FIGUR E | Molecular phylogeny of Streptophyta (and some Chlorophyta species) based on rbcL sequence comparisons. A phylogenetic tree was
inferred by Bayesian method (program MrBayes) with Bayesian Posterior Probabilities (PP) and maximum likelihood (ML) bootstrap support (BP)
indicated at nodes. From left to right, support values correspond to Maximum- Likelihood BP and Bayesian PP; BP values lower than 60% and PP
lower than 0.9 not shown. Strain in bold represents newly sequenced Streptof ilum strains.
14622920, 2025, 1, Downloaded from https://enviromicro-journals.onlinelibrary.wiley.com/doi/10.1111/1462-2920.70033 by Andreas Holzinger - Readcube (Labtiva Inc.) , Wiley Online Library on [08/01/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
10 of 15 Environmental Microbiology, 2025
strain O3- 3A- 2 differs from the authentic S. capillatum by sev-
eral morphological characters, like cell shape, thallus organisa-
tion and mucilage structure. Streptofilum is characterised by a
unique and outstanding cell coverage (Mikhailyuk etal.2018).
The cell coverage of strain O3- 3A- 2 was composed of the same
piliform scales, but they expanded much further in the broad
mucilage layers covering the sarcinoid cell packets formed by
this strain (Figure4A–H). Thus, it is likely that the formation of
piliform scales is a stable trait and all members of Streptofilum
have this kind of cell coverage. Some other early- branching
streptophytes are also covered by organic scales: Mesostigma
and Chlorokybus (Rogers, Mattox, and Stewart1980; Domozych,
Wells, and Shaw 1991). Moreover, zoospores and gametes of
Chaetosphaeridium, Coleochaete (both belong to the class
Coleochaetophyceae), Charophyceae and even some embryo-
phytes (e.g., Lycopodium, Psilotum) are covered by submi-
croscopic organic scales (Moestrup 1970; Maden, Renzaglia,
and Whittier 1996; van den Hoek, Mann, and Jahns 1996;
FIGUR E | Secondary structure of ITS2 from Strept ofil um arctic um sp. nov. O3- 3A- 2; pyrim idine- pyr imidine- mismatch (= typical for eukaryotic
algae) is indicated by the red arrow (GenBank accession number: PP849119).
FIGUR E | Effect of controlled desiccation (A) and rehydration (B) on the effective quantum yield (Y(II)) of PSII of three Streptofilum strains
(n = 4). Effective quantum yield values were standardised to the starting Y(II) to 100% for better comparison.
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11 of 15
Duncan, Renzaglia, and Garbary1997; Renzaglia et al.2001).
However, the structure and organisation of the cell coverage in
Streptofilum are distinct from the other mentioned Streptophyta
and Embryophyta, the latter characterised by scales of variable
complex structures and refined filigree shape clearly organised
like fish scales.
4.1 | Unique ITS2 Secondary Structure Underpins
Distinct Phylogenetic Position of Streptofilum
The rbcL phylogenetic tree shows Streptofilum in one cluster with
Chlorokybus, Mesostigma, Spirotaenia and other early- diverged
streptophytes algae; but distant from Klebsomidiophyceae and
Phragmoplastophyta. Although this is only a one gene phylog-
eny, the tree is in line with phylogenetic tree based on whole
chloroplast sequencing, which shows Streptofilum in- between
Chlorokybus and Klebsormidiophyceae (Glass et al. 2023). In
order to gain additional insight in the phylogenetic position of
Streptofilum, we estimated the secondary structure of the ITS2
region and compared its overall topology with other streptophyte
lineages. The resulting ITS2 secondary structure of Streptofilum
has common but also distinguishing features to other strepto-
phyte algae. Members of the class Klebsormidiophyceae are
characterised by an ITS2 secondary structure with four helices
and an unbranched third helix (Glaser etal.2017; Mikhailyuk
et al. 2018; Samolov et al. 2019). The more basal strepto-
phytes Mesostigma and Spirotaenia show a secondary struc-
ture with four helices and a branched third helix (Figure S1).
Chlorokybus, in contrast, only has three helices and the third
is unbranched (Irisarri et al.2021). The ITS2 secondary struc-
ture of Streptofilum combined features of those streptophytes in
a unique way: it is characterised by three helices and the third
helix is branched. Consequently, the secondary structure of the
ITS2 supports the findings by previous studies (see Section1)
that the genus Streptofilum represents indeed an independent
lineage among the streptophytes.
4.2 | Description of Streptofilum arcticum sp. nov
The molecular analyses and morphological features confirmed
that the new strains (Hg- 2- 4 and O3- 3- 2A) also belong to the
genus Streptofilum. The strain Hg- 2- 4 as well as both American
strains (ZNP2- V and BC4- VF) were identified as S. capillatum,
because of the morphological (only for Hg2- 4 available) and mo-
lecular similarity to the authentic strain S. capillatum SAG2559.
However, the Arctic strain O3- 3A- 2 exhibits differences in SSU
rRNA and rbcL sequences as well as a specific morphology with
massive cell coverage containing pili- shaped scales, and it was
FIGUR E | Photosynthetic- irradia nce curve of three Streptofilum strains (A–C). The points represent the mean of the measured values
(n = 4 ± standard deviation), and the dotted line is the fitting cur ve after Walsby(1997). Parameters of the PI curve are given in Table2. Temperature-
dependent oxygen production in three Streptofilum strains (D–F). The points represent the mean of the measured values (n = 4 ± standard deviation),
grey colour represents the respiration in the dark, black the photosynthesis. Dotted lines are the fitting curves after Yan and Hunt(1999). (A, D)
Streptofilum capillatum SAG 2559, (B, E) Streptofilum capillatum Hg- 2- 4, (C, F) Streptofilum arcticum sp. nov. O3- 3A- 2.
TABLE | Parameters of PI- curve (Figure8) for three Streptofilum
strains (±standard deviation).
SAG 2559 Hg- 2- 4 O3- 3A- 2
NPPmax 78 .1 ± 5.37 127 ± 19.9 7 105.1 ± 13.36
α0.89 ± 0.13 1.01 ± 0.13 1.02 ± 0.14
Ik91.4 ± 6 .96 129.3 ± 4.64 105.9 ± 3.95
Ic4.27 ± 0.78 3.51 ± 0.81 2.89 ± 1.14
Respiration −3.68 ± 0.6 −3.46 ± 1.16 −2.85 ± 0 .82
Abbreviations: α, light utilisation coeff icient; lc, light compensation point,
respiration is given in μ mol O2 mg−1 Chl a h−1; lk, light saturation point; pmax,
maximum oxygen production in μmol O2 mg−1 Chl a h−1.
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12 of 15 Environmental Microbiology, 2025
found in a special habitat and locality. Therefore, the descrip-
tion of a new species of the monotypic genus Streptofilum is
proposed.
Streptofilum arcticum Mikhailyuk, Glaser, Holzinger et Karsten
sp. nov. (Figures1H–K, 2, and 4).
Description: Thallus sarcinoid, forming 2–4 packet- like and
rarely short filamentous- like aggregations, often disintegrated
to diads and unicells. Cells naked, surrounded by variably dense
layers of piliform scales, visible in TEM micrographs possibly
of organic nature and thick (to 5.0–10.0 μm) layered mucilage
with waved edge. Mucilaginous caps on cells and layered finely
structured mucilage are especially prominent in old cultures.
Mucilaginous colonies resemble Radiococcaceae- like general
morphology. Vegetative cells widely ellipsoid to almost spheri-
cal, (5.1)6.4–7.6(11.0) μm in length and (4.2)–5.5–6.9(8.6) μm in
width. Chloroplast parietal, plate- shaped, with smooth or waved
margin and a single pyrenoid surrounded by several starch
grains. Vegetative reproduction by cell division in several planes
(sporulation- like type) and formation of sporangia with 2–4 (8)
cells. Sexual reproduction not observed.
Habitat: biological soil crusts, Arctic tundra top soil.
Type locality: vicinities of the Ny- Ålesund Research Station
(Svalbard, Norway), Ossian- Sarsfjellet, tundra top soil, biolog-
ical soil crusts, 78.95238° N, 12.49632° E.
Holotype (designated here): KW- A- 32535, preserved culture ma-
terial of authentic strain O3- 3A- 2 (IBASU- A- 781), Algotheca,
Herbarium of the M.G. Kholodny Institute of Botany of the
National Academy of Sciences of Ukraine (KW).
Isotype (designated here in support of the holotype): Preserved
specimen 240,521 fixed for TEM, resin embedded material of
strain O3- 3A- 2 is available for reference at the Department of
Botany, University of Innsbruck, Austria.
Iconotype (designated here in support of the holotype):
Figures1H–K, 2 and 4A–H.
Authentic strain: O3- 3A- 2 was deposited in IBASU- A, M.G.
Kholodny Institute of Botany of NASU of Ukraine, Kyiv,
Ukraine, under number IBASU- A- 781.
Etymology: arcticum = from Latin word arcticum—Аrctic.
4.3 | Ecophysiological Performance Indicates
Adaptation to Terrestrial Habitats
The desiccation tolerance of Streptofilum spp. was evaluated at
47% RH, where it lost its photosynthetic activity within ~2 h, but
fully recovered after rewetting within few minutes, and could
maintain ~80% of its initial value after 24 h. Previous experi-
ments revealed that S. capillatum SAG 2559 could not recover
under harsher conditions at 10% RH (Pierangelini etal. 2019).
The latter results could be confirmed for both new Streptofilum
strains, which did not recover photosynthesis after rapid desic-
cation at ~10% RH (data not shown). Other terrestrial algae, like
Klebsormidium and its relative Entransia and Hormidiella, could
recover at least to 50 % of initial performance even under extreme
and rather unnatural conditions of around 10% RH (Herburger,
Karsten, and Holzinger 2016; Donner etal. 2 017; Pierangelini
et al. 2019). Streptofilum cell aggregates easily disintegrate
into single cells, which are more prone to desiccation than fil-
aments or cell packets, which characterises Klebsormidium and
Entransia. This could be one reason, why Streptofilum could not
recover after harsh desiccation (Holzinger and Karsten2013). In
mesic and Arctic regions, the natural habitats of the analysed
Streptofilum strains, the RH drops down to 10% only rarely and
never in such rapid way like under experimenta l conditions when
directly exposed to silica gel (Pierangelini etal.2019). Thus, the
milder desiccating conditions at 47% RH better reflect natural
conditions and both Streptofilum species proved desiccation
tolerant with a fast and nearly full recovery of photosynthetic
activity. The geographic origin of the Streptofilum strains was
not reflected in the respective desiccation tolerance. Although
Spitzbergen is characteri sed by a lower annual precipitation than
Central Europe, it exhibits drastic changes in the environmen-
tal conditions because of climate change. Due to the influence
of the Gulf Stream and the so- called Arctic amplification par-
ticularly western Spitzbergen experiences higher summer and
winter temperatures then in previous decades, about 409 mm
annual precipitation, more melt- water from glaciers and more
rain- on- snow events in winter (Pedersen etal. 2022). All these
climatic and hydrological changes not only lead to more water
availability in the tundra over the course of the seasons, thereby
supporting the so- called Arctic greening (Pedersen etal.2022),
but also might explai n the less- pronounced desiccation tolerance
TABLE | Parameters of oxygen production or consumption along a temperature gradient after fitting with Yan and Hunt model (Figure 8)
including 5% confidence interval for three Streptofilum strains.
SAG 2559 Hg- 2- 4 O3- 3A- 2
pmax 55.6 (51.1–60.1) 67.8 (57.6–77.9) 87 (82–9 2.1)
Optimum temperature P (°C) 26.5 (25–27) 25.3 (22.4–28.2) 27.3 (26.2–28.3)
Maximum temperature P (°C) 44.4 (43.3–45.5) 43.8 (41.8–45.7) 44.5 (43.8–45.3)
Respiration max −20.6 (−15.96 to −25.14) −36.5 (−47 to −26.1) −34.8 (−29.1 to −40.5)
Optimum temperature resp. (°C) 36 .7 (33.5–39. 8) 33.9 (30.6 –37.1) 37 (35.5–38.6)
Maximum temperature resp. (°C) 51 (44–58 .1) 44.5 (42.7–46.2) 47.1 (45.3– 4 8.9)
Abbreviations: pmax, ma ximum oxygen production in μmol O2 mg−1 Chl a h−1; respiration max, max imum oxygen consumption in μmol O2 mg−1 Chl a h−1.
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13 of 15
of the Arctic Streptofilum species. Additionally, the biocrust mi-
croecosystem, where Streptofilum strains Hg- 2- 4 and O3- 3A- 2
were isolated, provides in general less harsh environmental
conditions compared to bare soil: in terms of desiccation, the
consortium of biocrust organisms accumulate extrapolymeric
substances and hence a water- holding and protective matrix for
all cells (Colica etal.2014; Belnap, Weber, and Büdel2016).
Both Streptofilum species are well adapted to low- light condi-
tions indicated by the low light compensation point and the
high alpha value. On the other hand, Streptofilum did not show
any indication for photoinhibition even at high light conditions.
Adaption to low- light and tolerance of high- light conditions was
already described for other streptophyte algae and interpreted
as high photophysiological plasticity (Karsten, Herburger, and
Holzinger2016; Pierangelini etal. 2017). Biocrusts represent a
three- dimensional micro- ecosystem with steep vertical light
gradients because of shading effects by lichen and moss thalli,
algal filaments or aggregates, mucilage, soil particles and so on.
The high photophysiological plasticity of Streptofilum allows
growth at different vertical positions in the biocrust, that is, ex-
posure to high or low light conditions, which might represent a
competitive advantage compared to other algal species.
Most aero- terrestrial algal species are eurytherm and thus, the
broad temperature tolerance of all three Streptofilum strains is
in line with previous reports of other biocrusts algae (Donner
etal.2 017; Glaser etal.2023). In terrestrial habitats, like soil
surface or biocrusts, the environmental conditions can change
more drastic and faster than in aquatic ecosystems, and con-
sequently, broad temperature tolerance is required to thrive
in those habitats. The geographic origin of the Streptofilum
strains was not reflected by the respective temperature tol-
erance, all strains exhibited similar optima and ranges. This
is confirmed by data on other microalgal species which also
showed similar temperature tolerance ranges independent of
the geographic origin (Teoh, Phang, and Chu2013; Borchhardt
and Gründling- Pfaff2020).
Under experimental UV exposure, both S. capillatum strains
thrived, but S. arcticum sp. nov. did not grow although it sur-
vived the treatment. A previous publication indicated that
Streptofilum might be able to produce mycosporine- like amino
acid (MAAs), known UV sunscreen compounds (Pierangelini
et al. 2019). MAAs are wide- spread in marine and terres-
trial algae, including basal streptophytes, but missing in
Embryophytes (Hotter et al. 2018; Geraldes and Pinto 2021).
The streptophyte Klebsormidium synthesises and accumulates
various MAAs under UV exposure (Kitzing, Pröschold, and
Karsten2014; Hartmann etal. 2020). Future experiments will
clarify, if S. capillatum is capable to produce MAAs under UV
exposure and if this trait is missing in S . arcticum sp. nov., which
would explain the lack of growth under UV treatment.
5 | Conclusion
Streptofilum capillatum and the newly described strain S. arcti-
cum sp. nov. are early- diverged streptophyte algae character-
ised by a unique cell coverage. Three strains of Streptofilum
were investigated within this study regarding their morphol-
ogy, ultrastructure, molecular taxonomy and various ecophys-
iological traits, like photosynthetic performance under light
gradient, desiccation and temperature tolerance. The strain
Hg- 2- 4 isolated from coastal sand dunes was unambiguously
identified as S. capillatum. The Arctic strain O3- 3A- 2 differed
in SSU rRNA and rbcL sequences as well as some morphologi-
cal features from the authentic S. capillatum strain and hence
was described as a new species, S. arcticum sp. nov. The data
on ultrastructure, molecular phylogeny including the second-
ary structure of ITS2 region pointed towards a separate lineage
formed by Streptofilum, which is located among other early-
diverged lineages (Mesostigma, Chlorokybus) in Streptophyta
phylogeny. The ecophysiological experiments revealed that
Streptofilum is well adapted to its terrestrial habitat as it is eu-
rytherm, desiccation- tolerant and photophysiologically highly
plastic. All these traits guarantee ecological success and sur-
vival in biocrusts, and we assume that Streptofilum has a much
broader biogeographic distribution than reported so far. In ad-
dition, this study demonstrates that new species and even new
lineages can still be found even in common environments. In
general, the discovery of new species contributes to broaden
our knowledge on biodiversity, and holds the potential for new
biotechnological innovations regarding, for example, the pres-
ence of secondary metabolites. Such compounds like UV ab-
sorbing sunscreens could be used as environmentally friendly
sun protection for human skins.
Author Contributions
Karin Glaser: investigation, writing – original draft, visualization,
conceptualization, methodology, data curation. Tatiana Mikhailyuk:
writing – review and editing, methodology, visualization, data cura-
tion, investigation, funding acquisition, conceptualization. Charlotte
Permann: methodology, writing – review and editing, investigation.
Andre as Holzinger: writing – r eview and editing, metho dology, inves -
tigation, funding acquisition, resources. Ulf Karsten: funding acquisi-
tion, writing – review and editing, conceptualization, resources.
Acknowledgements
We would like to thank Sabrina Obwegeser, University of Innsbruck,
Austria for help in TEM sectioning and image generation, Ancuela
Andosch, University of Salzburg, Austria for expert technical assis-
tance in HPF/FS and help in image generation. Our sincere thanks
are extended to: Leon Pfeufer, University of Rostock, Germany for
conducting growth experiments; Jane Bonin for conducting desicca-
tion experiments; Niklas Plag for his support with PI curve and tem-
perature dependent oxygen production. This study was supported by a
Georg- Forster research fellowship from the Alexander von Humboldt
Foundation and the European Union's Horizon 2020 Research and
Innovation programme under Grant Agreement no. 871072 (TM). In
addition, sampling on Spitsbergen was funded through the 2015–2016
BiodivERsA COFU ND project CLIMARCTIC, with the national funder
of Germany (DFG KA899/33–1) to UK. This research was funded in
part by the Austrian Science Fund (FWF) 10.55776/P34181 to AH. For
open access purposes, the authors have applied a CC BY public copy-
right licence to any author accepted manuscript version arising from
this submission.
Conflicts of Interest
The authors declare no conflicts of interest.
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14 of 15 Environmental Microbiology, 2025
Data Availability Statement
Sequences were deposited at GenBank under the accession numbers
PP852206 and PP852205 for rbcL, PP844619 and PP844620 for SSU
rRNA and PP849119 for ITS2.
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