Content uploaded by Pieter Vanormelingen
Author content
All content in this area was uploaded by Pieter Vanormelingen on Feb 17, 2016
Content may be subject to copyright.
A preview of the PDF is not available
An Inordinate Fondness? The Number, Distributions, and Origins of Diatom Species
Abstract
The number of extant species of diatoms is estimated here to be at least 30,000 and probably ca. 100,000, by extrapolation from an eclectic sample of genera and species complexes. Available data, although few, indicate that the pseudocryptic species being discovered in many genera are not functionally equivalent. Molecular sequence data show that some diatom species are ubiquitously dispersed. A good case can be made that at least some diatom species and even a few genera are endemics, but many such claims are still weak. The combination of very large species numbers and relatively rapid dispersal in diatoms is inconsistent with some versions of the "ubiquity hypothesis" of protist biogeography, and appears paradoxical. However, population genetic data indicate geographical structure in all the (few) marine and freshwater species that have been examined in detail, sometimes over distances of a few tens of kilometres. The mode of speciation may often be parapatric, in the context of a constantly shifting mosaic of temporarily isolated (meta) populations, but if our "intermediate dispersal hypothesis" is true (that long-distance dispersal is rare, but not extremely rare), allopatric speciation could also be maximized.
... As part of the supergroup of Stramenopiles, diatoms are related to brown algae such as the giant kelp. After their emergence about 250 million years ago, they evolved into various shapes and occur as solitary single cells or chain-like colonies ( Fig. 1.7), spanning a size range of three orders of magnitude from 2µm to 2000µm (Mann, 1999, Mann andVanormelingen, 2013). Today, diatoms occupy a diverse range of ecological niches and occur in almost every aquatic environment from freshwater to marine habitats across all latitudes (Malviya et al., 2016). ...
Interactions between diatoms and bacteria are crucial for marine ecosystem functioning and the global climate as they largely govern primary production in marine systems and drive global biogeochemical cycles. Zooming in on the immediate surroundings of a diatom cell, a microhabitat for a diverse and overall mutualistic bacterial community can be found that enables reciprocal exchanges of metabolites benefiting both the diatom and its associated bacteria, which together form a discrete ecological unit – the holobiont. This thesis aims to improve our understanding of how diatom holobionts adapted to occupy Arctic or temperate niches and to which extent diatom-associated bacterial microbiomes help to adapt their host under environmental conditions relevant to climate change and associated climate change-mediated poleward range shifts. The main objectives are to (I) experimentally quantify the response of Arctic and temperate diatoms to abiotic factors that characterize their biogeographic separation and thereby identify potential bottlenecks for adaptation of Arctic diatoms and poleward range shifts of their temperate relatives; (II) determine the net effect of the bacterial microbiome on Arctic and temperate diatom growth under multi-driver settings of these factors to understand its role in host adaptation; (III) unravel how abiotic conditions affect diatom-associated bacterial microbiome community composition and the underlying hostmicrobiome interactions (IV) develop a methodological strategy to understand diatommicrobiome community dynamics on the single- (host-) cell level to enable necessary speciesspecific (in-situ) information of natural diatom microbiomes in the future.
... The following statement in searching for rare algal species under the microscope is definitely true: "A needle in the haystack" (Zizka et al. 2018) especially in case of diatoms, which are the megadiverse group of algae (Mann 1999). So far 12,000 diatom species have been described (Guiry 2012), but their estimated species number is between 30,000 and 100,000 (Mann and Vanormelingen 2013). Studying rarity in benthic diatom communities is not easy and it represents a particular challenge. ...
Biodiversity loss in freshwater is five times higher compared to terrestrial ecosystems and especially threatens rare species. However, even basic knowledge about rarity is missing in aquatic algal ecology, which could be the base of their conservation strategies. Therefore, we investigated rare species in benthic diatom communities of the River Danube’s network system using different rarity concepts. We found that rare and common species are of similar quantities on a regional scale. Genera with fewer taxa provided more rare taxa. The majority of the rare diatom species had small population size among which 45–47% were habitat specialists and geographically restricted, locating streams and river sections whose protection would be outstandingly important. Rare diatom species provided 25–50% higher variability of the communities than common ones. Beta-diversity was also primarily determined by rare species and was mostly driven by species replacement especially in case of specialized and localized rare taxa. Benthic diatom communities established complex community structures. In this network organization, rare species have a core species role with a large impact on the structure and function of the ecological community. Study of rarity is not evident and a number of factors distract it, therefore, we have to carefully consider these uncertainties when dealing with rarity.
... They play an imperative role in the aquatic ecosystem as an indicator to determine pollution, trophic status, and species diversity. Typically, they function as autotrophic and photosynthetic primary producers, forming the first rung of the tropic food chain and converting numerous inorganic chemicals into organic forms (Mann and Vanormelingen, 2013). Algae's role in human life has become the world's most renewable green source, with massive demand for various ecological and economic aspects. ...
Global attention on microalgae has attained an excellent level for its high values of nutrients and numerous bioactive molecules. Chlorococcum is a cultivable alga with enormous biological and commercial applications. The present study aims to profile the species Chlorococcum infusionum for its phytochemical and biological potentialities. The species was cultured at 25±2 °C with a light intensity of 2500 lux (maximum) and a 7.3-7.5 pH level using Bold’s Basal Medium and obtained 0.9-1.2 g/L dry biomass. The proximate experiment is witnessed with high values of carbohydrate (67.7±0.00%), protein (26.9±0.12%), moisture (8.41±1.37%), and fiber (12.00±1.45%). The FTIR fingerprinting analysis determined the existence of macromolecular pools. It included the various functional groups originating from polysaccharides, amino acids, proteins, lipids, carbohydrates, nucleic acids, nitriles, alcohols, and amines. The GCMS analysis of this species encompasses 19 compounds, of which 13 are well known for their bio-potentialities. Significant antimicrobial activities are noticed against E. coli (14±0.57 mm) and P. syringae (14±0.57 mm) at 75 µg/mL concentration. Also, it exhibited notable antioxidant ability (IC50 = 28.17 ± 1.45 µg/mL) and cytotoxicity (IC50 = 36.12±1.55 µg/mL). The fallout of this present attempt states that C. infusionum could be a promising alternative resource for other microalgae to increase large-scale productivity in response to providing sustainable life from nature.
... They play an imperative role in the aquatic ecosystem as an indicator to determine pollution, trophic status, and species diversity. Typically, they function as autotrophic and photosynthetic primary producers, forming the first rung of the tropic food chain and converting numerous inorganic chemicals into organic forms (Mann and Vanormelingen, 2013). Algae's role in human life has become the world's most renewable green source, with massive demand for various ecological and economic aspects. ...
Global attention on microalgae has attained an excellent level for its high values of nutrients and numerous bioactive molecules. Chlorococcum is a cultivable alga with enormous biological and commercial applications. The present study aims to profile the species Chlorococcum infusionum for its phytochemical and biological potentialities. The species was cultured at 25±2 °C with a light intensity of 2500 lux (maximum) and a 7.3–7.5 pH level using Bold’s Basal Medium and obtained 0.9–1.2 g/L dry biomass. The proximate experiment is witnessed with high values of carbohydrate (67.7±0.00%), protein (26.9±0.12%), moisture (8.41±1.37%), and fiber (12.00±1.45%). The FTIR fingerprinting analysis determined the existence of macromolecular pools. It included the various functional groups originating from polysaccharides, amino acids, proteins, lipids, carbohydrates, nucleic acids, nitriles, alcohols, and amines. The GCMS analysis of this species encompasses 19 compounds, of which 13 are well known for their bio-potentialities. Significant antimicrobial activities are noticed against E. coli (14±0.57 mm) and P. syringae (14±0.57 mm) at 75 µg/mL concentration. Also, it exhibited notable antioxidant ability (IC50 = 28.17 ± 1.45 µg/mL) and cytotoxicity (IC50 = 36.12 ± 1.55 µg/mL). The fallout of this present attempt states that C. infusionum could be a promising alternative resource for other microalgae to increase large-scale productivity in response to providing sustainable life from nature.
Diatoms, a diverse group of photosynthetic unicellular algae, have gained significant global attention due to their ecological importance and multifaceted applications in scientific research. Their ecological roles are critical, encompassing nutrient cycling, carbon sequestration, and primary productivity, which establish them as essential components of aquatic food webs. The remarkable species richness of diatoms underscores their evolutionary success and highlights their integral roles in both freshwater and marine ecosystems. In addition to their environmental significance, diatoms possess a rich biochemical profile comprising valuable compounds with immense potential for biotechnological applications. These applications span diverse fields, including biofuel production, pharmaceuticals, and wastewater remediation. Despite the vast diversity and biochemical richness of diatoms, laboratory cultivation and maintenance remain challenging. To address these challenges, two primary methodologies have been developed: xenic and axenic culture techniques. Xenic culture involves maintaining diatoms alongside associated microorganisms, thereby replicating natural conditions and preserving ecological interactions. In contrast, axenic culture techniques focus on isolating pure diatom strains by employing meticulous sterilization processes, enabling precise experimental manipulation and fundamental research. Understanding the significance of xenic and axenic cultivation methodologies is essential for unlocking the full potential of diatoms across diverse scientific domains. This review elaborates on the methodologies, scope, and applications of xenic and axenic culture techniques for diatoms. By examining the intricacies of these cultivation approaches, it seeks to provide insights into optimizing diatom culture practices, advancing research initiatives, and harnessing the biotechnological potential of these extraordinary microorganisms.
Not applicable.
Diatoms synthesize silica cell walls (frustules) with genetically encoded nano- to micropatterned morphologies that surpass current synthetic chemistry. Silaffins, highly post-translationally modified peptides found in frustules, facilitate biosilica formation and regulate silica architectures in vitro, in coordination with long-chain polyamines. However, the precise roles of silaffins in diatom frustule morphogenesis remain unclear. This study investigates the morphological and functional impacts of TpSil1 and TpSil3 on diatom frustule in the model organism Thalassiosira pseudonana using gene overexpression and CRISPR/Cas9-mediated knockout approaches. The inability to generate biallelic TpSil3 knockout mutants suggests that TpSil3 may be essential, possibly leading to lethality upon complete knockout. In contrast, biallelic TpSil1 knockout mutants also disrupted TpSil2 due to high sequence homology. Morphological analysis revealed distinct roles for these proteins: TpSil3 regulates overall cell size and macropore (fultoportula) density, while TpSil1/2 primarily contributes to macropore morphogenesis; mesopore (cribrum pore) patterns, however, remained consistent across the mutants. Beyond morphology, genetic manipulation of silaffins significantly affected diatom physiology. Overexpression of silaffins increased cellular silicification, while knockouts reduced silica deposition but enhanced cell growth and photosynthetic efficiency. Moreover, these modifications altered the physicochemical and optical properties of bulk frustules, enhancing potential applications in hemostasis, catalysis and photonics. This study elucidates the role of silaffins in frustule morphogenesis, linking frustule-associated proteins to diatom physiology and frustule properties, and provides a framework for engineering nanostructured silica through synthetic biology
Diatoms constitute one of the most diverse and ecologically important phytoplankton groups, yet their large-scale diversity patterns and drivers of abundance are unclear due to limited observations. Here, we utilize Tara Oceans molecular and morphological data, spanning pole to pole, to describe marine diatom diversity, abundance, and environmental adaptation and acclimation strategies. The dominance of diatoms among phytoplankton in terms of relative abundance and diversity is confirmed, and the most prevalent genera are Chaetoceros, Thalassiosira, Actinocyclus and Pseudo-nitzschia. We define 25 distinct diatom communities with varying environmental preferences illustrative of different life strategies. The Arctic Ocean stands out as a diatom hotspot with 6 of the diatom communities being exclusive to it. Light har- vesting and photoprotection are among the cellular functions in which natural diatom populations invest the bulk of their transcriptional efforts. This com- prehensive study sheds light on marine diatom distributions, offering insights to assess impacts of global change and oceanic anthropogenic impacts.
Glacier-fed streams (GFSs) are harsh environments hosting unique, highly specialized communities. Interestingly, glaciers and their GFSs are also present in Earth’s tropical regions, where environmental characteristics contrast with GFS conditions elsewhere. Yet, despite the unique and isolated nature of tropical GFSs, little is known about their inhabitants, even though they may disappear later this century with ongoing climate change. Here, we examined diatom communities from one of the last tropical African GFSs in the Rwenzori Mountains, Uganda, to characterize the composition and diversity of this unique system. Six sediment-associated biofilm samples were collected from two reaches of a stream draining the Mt. Stanley Glacier, and the resident diatom communities were studied morphologically using light and scanning electron microscopy, as well as through the sequencing of amplicons from extracted DNA (18S and rbcL). In general, morphological results agree well with barcoding results, but each individually provides irreplaceable insights. In total, we identify 24 morphotypes utilizing light microscopy, 101 diatom Amplicon Sequence Variants (ASVs) using 18S sequences, and 65 ASVs with rbcL. Across approaches, common genera include Achnanthidium, Psammothidium, Neidium, Cymbopleura, Eunotia, and Pinnularia. However, only about half of the diversity could be assigned to the species level across methodologies, including several of the most common taxa, indicating a high level of uniqueness. Accordingly, one of the most common taxa encountered is described here as a new species, Neidium rwenzoriense sp. nov. Our results emphasize the Rwenzori Mountains as a global hotspot for endemism, and the novelty of disappearing tropical GFSs as diatom habitats.
Keywords: diatom species, rbcL, 18S, eDNA, Neidium, Africa, tropical glacier
Microalgae are microscopic unicellular organisms that inhabit marine, freshwater, and moist terrestrial ecosystems. The vast number and diversity of microalgal species provide a significant reservoir of biologically active compounds, highly promising for biomedical applications. Diatoms are unicellular eukaryotic algae belonging to the class Bacillariophyceae. They possess intricately structured silica-based cell walls, which contain long-chain polyamines that play important roles in the formation of silica. Long-chain polyamines are uncommon polyamines found only in organisms that produce biosilica. Diatomite, which is a marine sediment of the remains of the silica skeleton of diatoms, could be an abundant source of biogenic silica that can easily be converted to silica particles. This concise review focuses on the biofabrication of polyamine-based nanosilica from diatoms and highlights the possibility of utilizing diatom biosilica as a nanocarrier for drug and siRNA delivery, bioimaging, and bone tissue engineering. The challenges that may affect diatom production, including environmental stresses and climate change, are discussed together with the prospect of increasing diatom-based biosilica production with the desired nanostructures via genetic manipulation.
Diatoms are the most species-rich group of algae. They are ecologically widespread and have global significance in the carbon and silicon cycles, and are used increasingly in ecological monitoring, paleoecological reconstruction, and stratigraphic correlation. Despite this, the species taxonomy of diatoms is messy and lacks a satisfactory practical or conceptual basis, hindering further advances in all aspects of diatom biology. Several model systems have provided valuable insights into the nature of diatom species. A consilience of evidence (the 'Waltonian species concept') from morphology, genetic data, mating systems, physiology, ecology, and crossing behavior suggests that species boundaries have traditionally been drawn too broadly; many species probably contain several reproductively isolated entities that are worth taxonomic recognition at species level. Phenotypic plasticity, although present, is not a serious problem for diatom taxonomy. However, although good data are now available for demes living in sympatry, we have barely begun to extend studies to take into account variation between allopatric demes, which is necessary if a global taxonomy is to be bulk. Endemism has been seriously underestimated among diatoms, but biogeographical and stratigraphic patterns are difficult to discern, because of a lack of trustworthy data and because the taxonomic concepts of many authors are undocumented. Morphological diversity may often be a largely accidental consequence of physiological differentiation, as a result of the peculiarities of diatom cell division and the life cycle.