M Roldán

Autonomous University of Barcelona, Cerdanyola del Vallès, Catalonia, Spain

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Publications (17)35.93 Total impact

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    ABSTRACT: During an ecological study of Chroothece (Rhodophyta) in a small river in a semi-arid region in south-east Spain it became clear that most cells have a high lipid content. As this suggested potential uses in biotechnology, this aspect was investigated further. The colonies, which occur in full sunlight, are typically orange-brown. Most, perhaps all, the yellow-orange colour is associated with their high carotenoid content, with the carotenoid to chlorophyll ratio up to 2.7. The fatty acid composition reached 35.3 % dry weight, this consisting mainly of omega-3 (5.9 %) and omega-6 (29.4 %) acids. The high proportion of docosahexaenoic acid (1.78 %), eicosapentaenoic acid (14.15 %), arachidonic acid (0.92 %) and γ-linolenic acid (0.78 %) suggests use for medical and dietary purposes. All cells have a high phycocyanin content; phycoerythrin is absent. The alga has a wide distribution globally and hence provides scope for selecting strains with optimum properties.
    Food Chemistry 04/2014; · 3.33 Impact Factor
  • M Roldán, C Ascaso, J Wierzchos
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    ABSTRACT: Halite deposits from the hyperarid zone of the Atacama Desert reveal the presence of endolithic microbial colonization dominated by cyanobacteria associated with heterotrophic bacteria and archaea. Using the lambda-scan (λ-scan) confocal laser scanning microscopy (CLSM) option, this study examines the autofluorescence emission spectra produced by single cyanobacterial cells found inside halite rocks and by their photosynthetic pigments. Photosynthetic pigments could be identified according to the shape of the emission spectra and wavelengths of fluorescence peaks. According to their fluorescence fingerprints, three groups of cyanobacterial cells were identified within this natural extreme microhabitat: (i) cells producing a single fluorescence peak corresponding to the emission range of phycobiliproteins and chlorophyll a, (ii) cells producing two fluorescence peaks within the red and green signal ranges, and (iii) cells only emitting low intensity fluorescence within the unspecific green fluorescence signal range. Photosynthetic pigment fingerprints emerged as indicators of the preservation state or viability of the cells. These observations were supported by a cell plasma membrane integrity test based on SYTOX Green DNA staining and by transmission electron microscopy ultrastructural observations of cyanobacterial cells.
    Applied and environmental microbiology 03/2014; · 3.69 Impact Factor
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    ABSTRACT: The ecology of Chroothece was studied in the highly calcareous Río Chícamo, south-east Spain, in order to explain its success there, but rarity elsewhere. The river, which originates mainly from an underground aquifer, has water with high conductivity, sulphate and nitrate but low phosphate concentrations, the latter mainly organic. Chroothece occurs in mats and in lobed colonies reaching 4 cm in the broadest dimension. The colony surface consists of one layer of cells, each of which is attached to a stalk, which dichotomizes when the cell divides; stalks often extend to the colony base. The central region of many mat cells and almost all colony cells has a yellow to orange-brown colour, associated with the numerous lipid droplets densely covering the surface of the pyrenoid and arms of the star-shaped chloroplast. Field material and laboratory isolates indicate that stalk formation occurs under moderate P limitation and both stalks and cell sheath show high phosphatase activities. This also occurred in a culture collection strain maintained for 30 years in a very P-rich medium, but then transferred to a moderately P-limiting medium (c. 0.9 mg l−1). We suggest that colony formation is initiated by aggregation of motile cells following P pulses in the water. Comparisons are made with Rivularia, a competitor in this nitrate-rich river, in spite of being a N2-fixer. One difference is that Chroothece cells lie at the periphery of the colonies and are therefore exposed to maximum sunlight, whereas Rivularia trichomes grow inside colonies with photoprotection by scytonemin. However, the ability to withstand heavy grazing pressure may be an especially important factor favouring Rivularia here.
    European Journal of Phycology 03/2014; 49(1):1-14. · 1.91 Impact Factor
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    ABSTRACT: The Atacama Desert is one of the oldest and driest deserts in the world and its hyper-arid core is described as "the most barren region imaginable". We used a combination of high-throughput sequencing and microscopy methods to characterize the endolithic microbial assemblages of halite pinnacles (salt rocks) collected in several hyper-arid areas of the desert. We found communities dominated by archaea that relied on a single phylotype of Halothece cyanobacteria for primary production. A few other phylotypes of salt-adapted bacteria and archaea, including Salinibacter, Halorhabdus, and Halococcus were major components of the halite communities, indicating specific adaptations to the unique halite environments. Multivariate statistical analyses of diversity metrics clearly separated the halite communities from that of the surrounding soil in the Yungay area. These analyses also revealed distribution patterns of halite communities correlated with atmospheric moisture. Microbial endolithic communities from halites exposed to coastal fogs and high relative humidity were more diverse; their archaeal and bacterial assemblages were accompanied by a novel algae related to oceanic picoplankton of the Mamiellales. In contrast, we did not find any algae in the Yungay pinnacles, suggesting that the environmental conditions in this habitat might be too extreme for eukaryotic photosynthetic life.
    Environmental Microbiology 12/2013; · 5.76 Impact Factor
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    ABSTRACT: This work characterizes a unicellular cyanobacterium with nearly spherical cells and thin outlined sheaths that divide irregularly forming small packets immersed in a diffluent mucilaginous layer. It was isolated growing on calcite speleothems and walls in a show cave in Collbató (Barcelona, Spain). Spectral confocal laser and transmission electron microscopies were used to describe the morphology, the fine structure and the thylakoid arrangement. The pigments identified were phycoerytrin, phycocyanin, allophycocyanin and chlorophyll a. The three-dimensional reconstructions, generated from the natural fluorescence z-stacks, evidenced a large surface area of nearly flat arm-like thylakoidal membranes connected to each other and forming a unified structure in a way that has never been described before. Phylogenetic analyses showed 95% homology to the strain Chroococcus sp. JJCM (AM710384). The phenotypic diacritic features do not correspond to any species currently described and the genetic traits support it being classified as an independent genus in the order Chroococcales and the family Chroococcaceae. Hence, we propose the name Chalicogloea cavernicola gen. nov. sp. nov. The type strain is Chalicogloea cavernicola-COLL 3T (=CCALA 975 T = CCAP 1424/1 T).
    INTERNATIONAL JOURNAL OF SYSTEMATIC AND EVOLUTIONARY MICROBIOLOGY 11/2012; · 2.11 Impact Factor
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    ABSTRACT: Surfaces of buildings at the archaeological site of Palenque, Mexico, are colonized by cyanobacteria that form biofilms, which in turn cause aesthetic and structural damage. The structural characterization and species composition of biofilms from the walls of one of these buildings, El Palacio, are reported. The distribution of photosynthetic microorganisms in the biofilms, their relationship with the colonized substratum, and the three-dimensional structure of the biofilms were studied by image analysis. The differences between local seasonal microenvironments at the Palenque site, the bioreceptivity of stone and the relationship between biofilms and their substrata are described. The implications for the development and permanence of species capable of withstanding temporal heterogeneity in and on El Palacio, mainly due to alternating wet and dry seasons, are discussed. Knowledge on how different biofilms contribute to biodegradation or bioprotection of the substratum can be used to develop maintenance and conservation protocols for cultural heritage.
    Biofouling 05/2010; 26(4):399-409. · 3.40 Impact Factor
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    ABSTRACT: The Atacama Desert is considered to be the driest desert on Earth. The only sources of liquid water in its hyper-arid region are dew and fog. Both in terms of soil chemistry and liquid water availability, the Atacama Desert represents the best terrestrial analogue to the extreme arid conditions on Mars [1]. Therefore, the study of terrestrial life in hyper-arid deserts provides a first approximation to assessing the potential for life on Mars. We have recently shown that primary productivity in the Atacama Desert could occur within hygroscopic halite crusts [2], and that this is likely due to mineral deliquescence, which provides liquid water at relative humidity well below atmospheric condensation levels [3]. Gypsum and anhydrite are also widely distributed throughout the Atacama Desert and represent other potential lithic habitats for microorganisms. The aim of this study was to characterize the endolithic microbial communities and their microhabitats within the evaporitic crusts. Discussion of Results The endoevaporitic community is represented mainly by primary producers, including cyanobacteria and free-living algae, which are accompanied by heterotrophic bacteria and archaea. The metabolism and physiology of endoevaporitic microorganisms remains largely unexplored. We hypothesize that the interior of evaporitic salts provides protection from extreme temperature fluctuations, radiation and at the same type favour the cells hydration when the surrounding environment remains stubbornly dry. The habitability of evaporitic minerals is constrained by high ionic-strength conditions that occur in the presence of liquid water. Following the analogy with Mars, we propose that this type of deposits may have provided one of the last available niches for a putative Martian biosphere.
    Geochimica et Cosmochimica Acta 01/2009; 73:A1439. · 3.88 Impact Factor
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    Monica Roldàn, Mariona Hernàndez-Mariné
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    ABSTRACT: Caves with dim natural light, and lighted hypogean environments, have been found to host phototrophic microorganisms from varioustaxonomic groups. These microorganisms group themselves into assemblies known as communities or biofilms, which are associated withrock surfaces. In this work, the phototrophic biofilms that colonise speleothems, walls and floors in three tourist caves (Spain) were studied.Confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM) were used to study these organisms and acquirethree-dimensional data on their biofilm structure. CLSM was used in a multi-channel mode whereby the different channels map individualbiofilm components. Cyanobacteria, green microalgae, diatoms, mosses and lichens were found to be grouped as biofilms that differedaccording to the sampling sites. The biofilms were classified into six types regarding their environmental conditions. These types weredefined by their constituent organisms, the thickness of their photosynthetic layers and their structure. Light-related stress is associated with lower biofilm thickness and species diversity, as is low humidity, and, in the case of artificially illuminated areas, the duration of lightexposure.
    International Journal of Speleology. 01/2009;
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    Mònica Roldán, Mariona Hernández-Mariné
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    ABSTRACT: The purpose of this study was to evaluate the potential of green light (GL) for preventing biofilm growth in areas of cultural patrimony, which are normally illuminated with artificial white light (WL). The aerophytic cyanobacterium Gloeocapsopsis magma, colonizer of caves, was cultured under either GL or WL and its morphology and ultrastructure were compared. Spectral analysis of pigments showed high levels of phycoerythrin. GL light quality affected the morphology of colonies, thickness and organization of the sheath, cell size and formation of storage products. At the fine structure level the number of thylakoids was significantly decreased, compared to WL grown cells. Cells from two-months and sixmonths old WL cultures did not differ either in the number or disposition of their thylakoids. Although G. magma exposed to GL survived in nature and in culture the unbalanced fine structure reveals the limits of its adaptation.
    Algological Studies 03/2008; 126(1):159-171.
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    ABSTRACT: Artificial illumination can harm works of art by inducing the development of photosynthetic biofilms. With the aim of preventing biodeterioration or esthetic damage to such surfaces, we evaluated and compared the effects of illuminating biofilms formed by Gloeothece membranacea (cyanobacteria) and Chlorella sorokiniana (Chlorophyta) using exclusively white or green light.
    Applied and Environmental Microbiology 05/2006; 72(4):3026-31. · 3.68 Impact Factor
  • Applied and environmental microbiology 04/2006; 72(4):3026-3031. · 3.69 Impact Factor
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    ABSTRACT: A new imaging technique for the analysis of fluorescent pigments from a single cell is reported. It is based on confocal scanning laser microscopy coupled with spectrofluorometric methods. The setup allows simultaneous establishment of the relationships among pigment analysis in vivo, morphology, and three-dimensional localization inside thick intact microbial assemblages.
    Applied and Environmental Microbiology 07/2004; 70(6):3745-50. · 3.68 Impact Factor
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    ABSTRACT: The distribution of biofilms, the diversity of phototrophic organisms, and their relation to environmental conditions were studied in three limestone cavities in the karstic Garraf massif (Barcelona, NE Spain). Sixty-two taxa: 28 Cyanobacteria (42.8% Chroococcales, 21.4% Oscillatoriales, 7.1% Nostocales and 28.6% Stigonematales), 11 Chlorophyta, 16 Bacillariophyta and 7 lichens were identified. The environmental data obtained at three cavities by measuring temperature, relative humidity and light, showed a clear gradient from the entrance to a certain depth beyond which they remained stable. In a broad sense, the existence of three different levels can be assumed: a) Entrance level. The microclimate was strongly influenced by the outdoors. Scarcely attenuated light and abiotic factors fluctuated throughout the year. On the highly illuminated dry rocks the microflora colonies were quite rich, with special abundance of mucilaginous biofilms composed of algae and cyanobacteria typical of terrestrial aerophytic or atmophytic habitats. The community dominated by Scytonema julianum thrived in areas protected from rain. Trentepohlia sp. and many crustose lichens, which had this alga as a photobiont, were abundant. b) Intermediate level, with moderate abiotic oscillations and low light (25-0.5 mV) that was not yet a stress factor.A mixture of species formed biofilms. Cyanobacteria were their most visible constituents, occasionally mixed with green algae and diatoms. Biofilm abundance diminished with decreasing irradiance. c) Deep level (< 1 mV) until light extinction, with stable abiotic factors (10°C and dew point humidity). Only a few species were able to colonize this dim light zone. The presence of remains and empty sheaths increased with decreasing irradiance, and except for Geitleria calcarea and Loriella osteophila, the algae were heavily colonized by bacteria and filamentous fungi.
    Nova Hedwigia 04/2004; 78(3-4):329-351. · 0.81 Impact Factor
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    ABSTRACT: Confocal Laser Scanning Microscopy (CLSM) was used to investigate aerophytic phototrophic biofilms thriving on artificially illuminated surfaces in Roman hypogean monuments, particularly the St. Callistus and Domitilla Catacombs (Rome, Italy). Phototrophic organisms were visualized by their in vivo pigment fluorescence, whereas extrapolymeric substances (EPS) and DNA structures of both photo- and heterotrophic microorganisms were revealed respectively with the carbohydrate recognising lectin Concanavalin-A conjugated with the fluorophore Alexa Fluor 488 and the fluorochrome Hoechst 33258 labels. Inherent fluorescences other than pigment fluorescence such as CaCO3 fluorescence of the substratum were also detected. Distribution of microorganisms and EPS in biofilms and their relationship with substratum was evidenced with the application of diverse kinds of image analyses. Detailed localization of certain structures or taxa was achieved with the examination of gallery images. On the other hand, particular image analyses enlightened one or several partial aspects of the biofilm heterogeneity. Extended focus images built with the maximum intensity projections of the x-y, x-z, and y-z planes were best to compare among biofilms and to reveal their porosity and stratification. 3D-reconstructions of biofilms as perspective images gave an account of the surface characteristics such as roughness or coverage of the substratum surface. Topographic reconstruction was used to measure geometrical and biological heterogeneity parameters like sample thickness or surface roughness. What makes CLSM so powerful is the ability to analyse samples with minimal preparation and non-disturbing architectural observation, the use of multiple excitation and detection wavelengths at different depths of focus, and the large pool of digital image processing algorithms with which one can effectively target specific elements in the biofilm sample, such as molecules (e.g. DNA and pigments), structure (e.g. surfaces, matrix, sheaths and filaments) and properties (e.g. stage of cell division, growth and senescence), with the capability to fully visualise them all in 3D image.
    Algological Studies 01/2004; 111(1):127-143.
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    ABSTRACT: Organisms building biofilms are of considerable interest in the context of degradation of cultural heritage. Particularly, hypogean environments exposed to artificial light are colonized by microbial communities, which damage walls and frescoes. In order to ascertain the mechanisms by which phototophic biofilms thrive under the particular conditions of hypogea, the organism composition and three-dimensional structure of biofilms from the Roman catacombs St. Callistus and Domitilla were studied. The main phototrophic organisms forming the biofilms were filamentous sheathed cyanobacteria and mosses. Biofilms were spatially very heterogeneous in thickness, density and organism composition but could be classified as regards their main organisms. There was a trend of decreasing diversity in the phototrophic composition of the biofilms under lower irradiances, the one at the lowest irradiance being uniquely built by erected filaments of Leptolyngbya sp. Except for this biofilm, the main organism composition was not clearly related with decreasing irradiance. However, biofilms from dim light samples were porous and the filamentous cyanobacteria in them were erected. Leptolyngbya sp., the most ubiquitous species, displayed a high number of phycobilisomes and its hormogonia a gliding movement that allowed colonization of substrata. Such mechanisms may have an important role for thriving under the low light conditions of the catacombs.
    Algological Studies 07/2003; 109(1):229-239.
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    M. Roldán
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    ABSTRACT: Photosynthetic biofilms thriving in dim subterranean monuments have been studied. Patches of heterogeneous biofilms developed on walls and works of art, causing patinas and coloured stains. These communities were composed of moss protonema, lichens, diatoms, rod-shaped green algae and coccal cyanobacteria (1). A combination of confocal laser scanning microscopy (CLSM) and spectrophotofluorometric detection (Leica TCS-SP2) were used to characterise the 3-D structures of intact, live biofilms and identify pigment signatures at a subcellular level (2, 3). 3-D imaging of biofilms revealed differences in the distribution of composite micro- organisms and their respective emission spectra in depth (Fig. 1). Biofilm types were identified according to their constituent organisms as either multi-species biofilms or stratified biofilms. Sampling points with natural light and low humidity contained stratified biofilms in which the top layer was formed of thin-trichome oscillatoriacean species and chlorophyta, and the bottom layer, of coccal cyanobacteria. Mosses, lichens and chlorophyta located at sampling points with natural light and percolation of meteoric waters were overgrown with diatoms. Fluorescence properties for x-y-λ single sections of each morphospecies were obtained at several excitation wavelengths. For each organism, the chlorophylls and phycobilins identified were correlated with its vertical position in its respective biofilm (Fig. 1). The detection method allowed direct analysis of samples for global and single pixel fluorescence, as well as in vivo 3D localisation. Moreover, the distinct fluorescence signatures of cells located within a colony could be correlated with cell morphology and individual cell states.