ENDOLITHIC MICROFLORA ARE MAJOR PRIMARY PRODUCERS IN DEAD CARBONATE SUBSTRATES OF HAWAIIAN CORAL REEFS1

To quantify the contribution of endolithic phototrophs to primary production of dead carbonate substrates, experimental blocks of cleaned Porites lobata Dana skeleton were placed at three different sites in Kaneohe Bay, Hawaii: inshore, lagoonal, and oceanic. After 6 months of exposure, experimental blocks were colonized by communities characteristic of their estuarine (inshore, lagoonal) and oceanic (ocean) environments. Blocks were sub-sampled; net photosynthesis (NP) and chl a concentrations of the whole blocks (epi- and endoliths) and scrapped blocks (only endoliths) were quantified. Green turf algae colonized predominantly inshore and lagoonal blocks, while encrusting corallines were the dominant epiliths colonizing oceanic blocks. Four main species of endolithic phototrophs were identified in all blocks: Mastigocoleus testarum Lagerheim, Plectonema terebrans Bornet and Flahault (cyanobacteria), Phaeophila dendroides Crouan and Crouan, and Ostreobium quekettii Bornet and Flahault (Chlorophytes). While epiliths were very different between sites, NP rates and chl a concentration of endoliths did not vary significantly and were positively correlated (191±25 mmol C·m⁻²·day⁻¹ and 590±150 mg chl a·m⁻² of reef, respectively). Assimilation numbers for whole communities, including both epilithic and endolithic communities, were similar to those measured for endolithic communities alone (average of 0.3 g C·g chl a·h⁻¹). Under experimental conditions, the contribution of endolithic phototrophs to community NP rates of blocks ranged from 56% to 81%, and under natural conditions, we estimated that this contribution ranged between 32% and 46%. Thus, we showed that the endolithic phototrophs are one of the major primary producers in dead coral substrates in a wide range of coral reef environments.     

Growth of elaborate microbial pinnacles in Lake Vanda,Antarctica

Microbial pinnacles in ice‐covered Lake Vanda, McMurdo Dry Valleys, Antarctica, extend from the base of the ice to more than 50 m water depth. The distribution of microbial communities, their photosynthetic potential, and pinnacle morphology affects the local accumulation of biomass, which in turn shapes pinnacle morphology. This feedback, plus environmental stability, promotes the growth of elaborate microbial structures. In Lake Vanda, all mats sampled from greater than 10 m water depth contained pinnacles with a gradation in size from <1‐mm‐tall tufts to pinnacles that were centimeters tall. Small pinnacles were cuspate, whereas larger ones had variable morphology. The largest pinnacles were up to ~30 cm tall and had cylindrical bases and cuspate tops. Pinnacle biomass was dominated by cyanobacteria from the morphological and genomic groups Leptolyngbya, Phormidium, and Tychonema. The photosynthetic potential of these cyanobacterial communities was high to depths of several millimeters into the mat based on PAM fluorometry, and sufficient light for photosynthesis penetrated ~5 mm into pinnacles. The distribution of photosynthetic potential and its correlation to pinnacle morphology suggests a working model for pinnacle growth. First, small tufts initiate from random irregularities in prostrate mat. Some tufts grow into pinnacles over the course of ~3 years. As pinnacles increase in size and age, their interiors become colonized by a more diverse community of cyanobacteria with high photosynthetic potential. Biomass accumulation within this subsurface community causes pinnacles to swell, expanding laminae thickness and creating distinctive cylindrical bases and cuspate tops. This change in shape suggests that pinnacle morphology emerges from a specific distribution of biomass accumulation that depends on multiple microbial communities fixing carbon in different parts of pinnacles. Similarly, complex patterns of biomass accumulation may be reflected in the morphology of elaborate ancient stromatolites.     

Microclimate and limits to photosynthesis in a diverse community of hypolithic cyanobacteria in northern Australia

Hypolithic microbes, primarily cyanobacteria, inhabit the highly specialized microhabitats under translucent rocks in extreme environments. Here we report findings from hypolithic cyanobacteria found under three types of translucent rocks (quartz, prehnite, agate) in a semiarid region of tropical Australia. We investigated the photosynthetic responses of the cyanobacterial communities to light, temperature and moisture in the laboratory, and we measured the microclimatic variables of temperature and soil moisture under rocks in the field over an annual cycle. We also used molecular techniques to explore the diversity of hypolithic cyanobacteria in this community and their phylogenetic relationships within the context of hypolithic cyanobacteria from other continents. Based on the laboratory experiments, photosynthetic activity required a minimum soil moisture of 15% (by mass). Peak photosynthetic activity occurred between approximately 8°C and 42°C, though some photosynthesis occurred between ?1°C and 51°C. Maximum photosynthesis rates also occurred at light levels of approximately 150–550 μmol m^?2 s^?1. We used the field microclimatic data in conjunction with these measurements of photosynthetic efficiency to estimate the amount of time the hypolithic cyanobacteria could be photosynthetically active in the field. Based on these data, we estimated that conditions were appropriate for photosynthetic activity for approximately 942 h (～75 days) during the year. The hypolithic cyanobacteria community under quartz, prehnite and agate rocks was quite diverse both within and between rock types. We identified 115 operational taxonomic units (OTUs), with each rock hosting 8–24 OTUs. A third of the cyanobacteria OTUs from northern Australia grouped with Chroococcidiopsis, a genus that has been identified from hypolithic and endolithic communities from the Gobi, Mojave, Atacama and Antarctic deserts. Several OTUs identified from northern Australia have not been reported to be associated with hypolithic communities previously.     

Hypolithic microbial communities of quartz rocks from Miers Valley, McMurdo Dry Valleys, Antarctica

The McMurdo Dry Valleys region of eastern Antarctica is a cold desert that presents extreme challenges to life. Hypolithic microbial colonisation of the subsoil surfaces of translucent quartz rocks represent a significant source of terrestrial biomass and productivity in this region. Previous studies have described hypoliths as dominated by cyanobacteria. However, hypoliths that occur in the lower Dry Valleys such as the Miers, Garwood and Marshall Valleys are unusual as they are not necessarily cyanobacteria-dominated. These hypoliths support significant eukaryal colonisation by fungi and mosses in addition to cyanobacteria-dominated bacterial assemblages and so have considerable ecological value in this barren landscape. Here, we characterise these novel hypoliths by analysis of environmental rRNA gene sequences. The hypolithic community was demonstrated to be distinct from the surrounding soil and non-translucent rocks. Hypoliths supported cyanobacterial signatures from the Oscillatoriales and Nostocales. Other heterotrophic bacterial signatures were also recovered, and these were phylogenetically diverse and spanned 8 other bacterial phyla. Archaeal phylotypes recovered were phylogenetically affiliated with the large group of unclassified, uncultured Crenarcheota. Eukaryal phylotypes indicated that free-living ascomycetous fungi, chlorophytes and mosses (Bryum sp.) were all supported by these hypoliths, and these are thought to be responsible for the extensive eukaryotic biomass that develops around quartz rocks.     

Extremely low lichen growth rates in Taylor Valley,Dry Valleys,continental Antarctica

Estimates of lichen growth rates based on the measurements of several thalli at any site do not exist for continental Antarctica. However, the very limited existing data suggest that lichen growth rate may be a good indicator of climate change in Antarctica. We present measurements made on thalli of the lichen Buellia frigida Darb. growing in the Dry Valleys, Southern Victoria Land, continental Antarctica, which appear to have some of the slowest radial growth rates yet measured. Photographs of thalli at three different sites were analysed for growth over a 25-year period using nano-GIS techniques. At one site, Mt. Falconer Summit, the lichens had a mean growth rate of 0.0052 mm year⁻¹ with one individual as low as 0.0036 mm year⁻¹. Thalli at the other two sites had significantly higher mean growth rates, 0.0136 mm year⁻¹ at Mt. Falconer Ridge and 0.0118 mm year⁻¹ at Rhone Bench. Assuming a constant growth rate, thalli at Mt. Falconer Summit had a mean age of 5,367 years, whilst the thalli at the other two sites were much younger, 840–1,026 years. We suggest that the different ages represent the appearance of new substrate for colonisation following climate changes in the Dry Valleys that altered the amount and duration of snow. The results confirm that lichen growth rate differs by almost two orders of magnitude over a latitudinal range of 15 degrees from south to north across Antarctica.     

ALGAL BIOMASS AND PRIMARY PRODUCTION WITHIN A TEMPERATE ZONE SANDSTONE

The use of dimethyl sulfoxide (DMSO) to extract chlorophyll a and ^l4C-labelled photosynthate from endolithic algae of sparsely vegetated, cold temperate grasslands on the Colorado Plateau in Arizona has yielded the first estimates of biomass and photosynthesis for this unusual community. These subsurface microorganisms are found widespread in exposed Coconino Sandstone, a predominant formation in this cold temperate region. The endolithic community in Coconino Sandstone, composed primarily of coccoid blue-green and coccoid/sarcinoid green algae, yielded a biomass value (as chlorophyll a content) of 87 mg m^-2 rock surface area and a photosynthetic rate of 0.37 mg CO₂ dm ² hr^-1 or 0.48 mg CO₂ mg^-1 chl a hr^-1. The endolithic algal community contributes moderate biomass (5–10%) and substantial photosynthesis (20–80%) to the sparse grassland ecosystem.     

Microbial Community Changes Elicited by Exposure to Cyanobacterial Allelochemicals

An increasing body of evidence points out that allelopathy may be an important process shaping microbial communities in aquatic ecosystems. Cyanobacteria have well-documented allelopathic properties, mainly derived from the evaluation of the activity of allelopathic extracts or pure compounds towards monocultures of selected target microorganisms. Consequently, little is known regarding the community dynamics of microorganisms associated with allelopathic interactions. In this laboratory-based study, a Microcystis spp.-dominated microbial community from a freshwater lake was exposed, for 15 days, to exudates from the cyanobacterium Oscillatoria sp. strain LEGE 05292 in laboratory conditions. This cyanobacterium is known to produce the allelochemicals portoamides, which were among the exuded compounds. The community composition was followed (by means of polymerase chain reaction followed by denaturing gradient gel electrophoresis and microscopic analyses) and compared to that of a non-exposed situation. Following exposure, clear differences in the community structure were observed, in particular for cyanobacteria and unicellular eukaryotic taxa. Interestingly, distinct Microcystis genotypes present in the community were differentially impacted by the exposure, highlighting the fine-scale dynamics elicited by the exudates. These results support a role for cyanobacterial allelochemicals in the structuring of aquatic microbial communities.     

Phylogenetic diversity of endolithic bacteria in Bole granite rock in Xinjiang

The endolithic environment is a ubiquitous microbial habitat for microorganisms, such as lichens, Cyanobacteria and fungi, and it provides mineral nutrients and growth surfaces. In extremely environments, such as hot and cold desert, endolithic communities are often the main form of life. More recently, endolithic microbial communities have been observed inhabiting a variety of rock types ranging from hard granite to porous rocks such as basalt, dolomite, limestone, sandstone and granites. Regardless of geographic location and rock type, each of these habitats is characterized by a subsurface microclimate that prevents endolithic microorganisms growth. Photosynthesis-based endolithic microbial communities commonly inhabit the outer millimeters to centimeters of rocks exposed to the surface. The ability to fix carbon dioxide and in some cases atmospheric dinitrogen, gives the Cyanobacteria a clear competitive advantage over heterotrophic bacteria, so it is been called the main primary producer. Light quality and intensity appear to be the main determinant of the maximum depth to which growth occurs in endolithic phototrophic communities. Valleys of Fantastic Rocks in Bole is close to Alashankou Port of Xinjiang which belongs to extreme continental climate. In order to investigate the structure, composition and diversity of endolithic bacterial community in exposed granitic porphyry in the Valleys of Fantastic Rocks, environmental DNA was directly extracted from granite rock, the 16S rRNA genes were amplified from the total DNA by PCR with bacterial-specific primers, and an endolithic bacterial clone library was constructed. Positive clones were randomly selected from the library and identified by Restriction Fragment Length Polymorphism (RFLP). The unique rRNA types clones were sequenced, analysised and then constructed phylogenetic tree. In total, 129 positive clones were screened and grouped into 46 operational taxonomic unites (OTUs). The clone coverage C value was 89.15%, indicating that most of the estimated endolithic bacterial diversity was sampled. BLAST analysis indicated that 46 OTUs were divided into seven phyla (Acidobacteria, Actinobacteria, Bacteroidetes, Chloroflexi, Cyanobacteria, Planctomycetes, Proteobacteria) and five unknown groups. Cyanobacteria (43%), especially the Gp I, form the functional basis for an endolithic bacteria community which contain a wide spectrum species of chemotrophic bacteria (33%) with mainly Actinobacteria, α-Proteobacteria, Acidobacteria. Additionally, most clones that derived from the endolithic bacteria clone library showed high similarity to the sequence deposited in GenBank database with 97%–99%. Besides, 35% of the clones showed less than 97% of sequence similarity, of which 12% sequences were affiliated to genus Rubrobacter. The results suggested that endolithic bacteria in Valleys of Fantastic Rocks in Xinjiang were highly diverse in species richness, and maybe have a diversity of potential novel species and lineages.     

The Extremophile Endolithella mcmurdoensis gen. et sp. nov. (Trebouxiophyceae,Chlorellaceae), A New Chlorella-like Endolithic Alga From Antarctica

The McMurdo Dry Valleys constitute the largest ice-free region of Antarctica and one of the most extreme deserts on Earth. Despite the low temperatures, dry and poor soils and katabatic winds, some microbes are able to take advantage of endolithic microenvironments, inhabiting the pore spaces of soil and constituting photosynthesis-based communities. We isolated a green microalga, Endolithella mcmurdoensis gen. et sp. nov, from an endolithic sandstone sample collected in the McMurdo Dry Valleys (Victoria Land, East Antarctica) during the K020 expedition, in January 2013. The single non-axenic isolate (E. mcmurdoensis LEGE Z-009) exhibits cup-shaped chloroplasts, electron-dense bodies, and polyphosphate granules but our analysis did not reveal any diagnostic morphological characters. On the basis of phylogenetic analysis of the 18S rRNA (SSU) gene, the isolate was found to represent a new genus within the family Chlorellaceae.     

Spatial Dominance and Inorganic Carbon Assimilation by Conspicuous Autotrophic Biofilms in a Physical and Chemical Gradient of a Cold Sulfurous Spring: The Role of Differential Ecological Strategies

The community composition and ecophysiological features of microbial autotrophic biofilms were studied in Fuente Podrida, a cold sulfur spring located in East Spain. We demonstrated how different ecophysiological strategies, such as resistance and/or utilization of sulfide and oxygen, light adaptation, or resistance to high water flow, allow each of the microorganisms described to efficiently colonize several areas within the environmental gradient. In the zone of the spring constantly influenced by sulfide-rich waters, biofilms were formed by purple bacteria, cyanobacteria, and filamentous colorless sulfur bacteria. Purple bacteria showed higher photosynthetic efficiency per pigment unit than cyanobacteria, although they were dominant only in anoxic areas. Two filamentous cyanobacteria, strain UVFP1 and strain UVFP2, were also abundant in the sulfide-rich area. Whereas the cyanobacterial strain UVFP2 shows a strategy based on the resistance to sulfide of oxygenic photosynthesis, strain UVFP1, additionally, has the capacity for sulfide-driven anoxygenic photosynthesis. Molecular phylogenetic analyses cluster the benthic strain UVFP1 with genus Planktothrix, but with no particular species, whereas UVFP2 does not closely cluster with any known cyanobacterial species. The colorless sulfur bacterium Thiothrix sp. extended throughout the zone in which both sulfide and oxygen were present, exhibiting its capacity for chemolithoautotrophic dark carbon fixation. Downstream from the source, where springwater mixes with well-oxygenated stream water and sulfide disappears, autotrophic biofilms were dominated by diatoms showing higher photosynthetic rates than cyanobacteria and, by a lesser extent, by a sulfide-sensitive cyanobacterium (strain UVFP3) well adapted to low light availability, although in the areas of higher water velocity far from the river shore, the dominance shifted to crust-forming cyanobacteria. Both types of microorganisms were highly sensitive to sulfide impeding them from occupying sulfide-rich areas of the spring. Sulfide, oxygen, light availability, and water velocity appear as the main factors structuring the autotrophic community of Fuente Podrida spring. An erratum to this article is availbale at .     

Microbial diversity of cryptoendolithic communities from the McMurdo Dry Valleys,Antarctica

In the McMurdo Dry Valleys of Antarctica, microorganisms colonize the pore spaces of exposed rocks and are thereby protected from the desiccating environmental conditions on the surface. These cryptoendolithic communities have received attention in microscopy and culture-based studies but have not been examined by molecular approaches. We surveyed the microbial biodiversity of selected cryptoendolithic communities by analyzing clone libraries of rRNA genes amplified from environmental DNA. Over 1,100 individual clones from two types of cryptoendolithic communities, cyanobacterium dominated and lichen dominated, were analyzed. Clones fell into 51 relatedness groups (phylotypes) with > or =98% rRNA sequence identity (46 bacterial and 5 eucaryal). No representatives of Archaea were detected. No phylotypes were shared between the two classes of endolithic communities studied. Clone libraries based on both types of communities were dominated by a relatively small number of phylotypes that, because of their relative abundance, presumably represent the main primary producers in these communities. In the lichen-dominated community, three rRNA sequences, from a fungus, a green alga, and a chloroplast, of the types known to be associated with lichens, accounted for over 70% of the clones. This high abundance confirms the dominance of lichens in this community. In contrast, analysis of the supposedly cyanobacterium-dominated community indicated, in addition to cyanobacteria, at least two unsuspected organisms that, because of their abundance, may play important roles in the community. These included a member of the alpha subdivision of the Proteobacteria that potentially is capable of aerobic anoxygenic photosynthesis and a distant relative of Deinococcus that defines, along with other Deinococcus-related sequences from Antarctica, a new clade within the Thermus-Deinococcus bacterial phylogenetic division.     

THE RELATIONSHIP OF LIPIDS WITH LIGHT AND CHLOROPHYLL MEASUREMENTS IN FRESHWATER ALGAE AND PERIPHYTON1

Lipid content and lipid class composition were determined in stream periphyton and the filamentous green algae Cladophora sp. and Spirogyra sp, Sterols and phospholipids were compared to chlorophyll a (chl a) as predictors of biomass for stream periphyton and algae. Chlorophyll a, phospholipids, and sterols were each highly correlated with ash-free dry mass (AFDM) (r² > 0.98). Stream periphyton exposed naturally to high light (HL) and low light (LL) had chl a concentrations (μg chl a-mg^?1AFDM) of 7.9± 0.7 and 12.4 ± 2.9, respectively, while the sterol concentrations of these HL and LL stream periphyton (1.6 ± 0.4) were not significantly different (P > 0.05). Periphyton exposed to an irradiance of 300 μmol photons·m^?2s^?1 in the laboratory for 60 h had 5.6 ± 0.55 μg chl a·mg^?1 AFDM, but the same periphyton exposed to 2% incident light for the same amount of time had 11.0 ± 0.56 μg chl a·mg^?1 AFDM. Sterol concentrations in these periphyton communities remained unchanged (1.5 ± 0.3 μg·mg^?1AFDM), Similar results (i.e. changes in chl a but stability of sterol concentrations in response to irradiance changes) were also found for Cladophora and Spirogyra in laboratory experiments. Sterols can be quantified rapidly from a few milligrams of algae and appear to be a useful predictor of eukaryote biomass, whereas cellular levels of chl a vary substantially with light conditions. Phospholipids (or phospholipid fatty acids) are considered to be a reliable measure of viable microbial biomass. Nevertheless, phospholipid content varied substantially and unpredictably among algae and periphyton under different light regimes. Irradiance also had a significant effect on storage lipids: HL Cladophora and HL periphyton had 2 × and 5 × greater concentrations of triacylglycerols, respectively, compared to their LL forms. HL and LL algae also differed in the concentration of several major fatty acids. These light-induced changes in algal lipids and fatty acids have important implications for grazers.     

THE CYANOBACTERIAL CHLOROPHYLL‐BINDING‐PROTEIN ISIA ACTS TO INCREASE THE IN VIVO EFFECTIVE ABSORPTION CROSS‐SECTION OF PSI UNDER IRON LIMITATION1

Iron availability limits primary production in >30% of the world’s oceans; hence phytoplankton have developed acclimation strategies. In particular, cyanobacteria express IsiA (iron‐stress‐induced) under iron stress, which can become the most abundant chl‐binding protein in the cell. Within iron‐limited oceanic regions with significant cyanobacterial biomass, IsiA may represent a significant fraction of the total chl. We spectroscopically measured the effective cross‐section of the photosynthetic reaction center PSI (σ_PSI) in vivo and biochemically quantified the absolute abundance of PSI, PSII, and IsiA in the model cyanobacterium Synechocystis sp. PCC 6803. We demonstrate that accumulation of IsiA results in a ～60% increase in σ_PSI, in agreement with the theoretical increase in cross‐section based on the structure of the biochemically isolated IsiA‐PSI supercomplex from cyanobacteria. Deriving a chl budget, we suggest that IsiA plays a primary role as a light‐harvesting antenna for PSI. On progressive iron‐stress in culture, IsiA continues to accumulate without a concomitant increase in σ_PSI, suggesting that there may be a secondary role for IsiA. In natural populations, the potential physiological significance of the uncoupled pool of IsiA remains to be established. However, the functional role as a PSI antenna suggests that a large fraction of IsiA‐bound chl is directly involved in photosynthetic electron transport.     

Identification of a Diagnostic Marker To Detect Freshwater Cyanophages of Filamentous Cyanobacteria

Cyanophages are viruses that infect the cyanobacteria, globally important photosynthetic microorganisms. Cyanophages are considered significant components of microbial communities, playing major roles in influencing host community diversity and primary productivity, terminating cyanobacterial water blooms, and influencing biogeochemical cycles. Cyanophages are ubiquitous in both marine and freshwater systems; however, the majority of molecular research has been biased toward the study of marine cyanophages. In this study, a diagnostic probe was developed to detect freshwater cyanophages in natural waters. Oligonucleotide PCR-based primers were designed to specifically amplify the major capsid protein gene from previously characterized freshwater cyanomyoviruses that are infectious to the filamentous, nitrogen-fixing cyanobacterial genera Anabaena and Nostoc. The primers were also successful in yielding PCR products from mixed virus communities concentrated from water samples collected from freshwater lakes in the United Kingdom. The probes are thought to provide a useful tool for the investigation of cyanophage diversity in freshwater environments.     

Thermostablility of phycobiliproteins and antioxidant activity from four thermotolerant cyanobacteria

Four cyanobacterial strains including Cyanosarcina sp. SK40, Phormidium sp. PD40‐1, Scytonema sp. TP40 and Leptolyngbya sp. KC45 were selected and investigated for the phycobiliprotein (PBP) content and thermostable antioxidant activity of their cell‐free extracts. The highest content of 181.63 mg/g dry weight phycobiliprotein was found in Leptolyngbya sp. KC45 with phycoerythrin (PE) as the main phycobiliprotein. Among the PBPs of four thermotolerant cyanobacteria, PE from Leptolyngbya sp. KC45 exhibited the highest thermal stability as 80% of the original level remained after being heated at 60°C for 30 min. Antioxidant activities were detected in the cell‐free extracts of all cyanobacteria and that of Leptolyngbya sp. KC45 was also found in the highest value of 7.44 ± 0.14 and 3.89 ± 0.08 mg gallic acid equivalent (GAE) g^?1 dry weights determined by 2,2‐diphenyl‐1‐picrylhydrazyl radical (DPPH) and reducing power assay, respectively. This also corresponded to the phenolic compound content. Based on DPPH and reducing power assay, antioxidant activities of all cyanobacterial extracts showed the high thermostability as approximately 80% remained after being heated at 80°C for 30 min. However, it clearly indicated that the thermostability of antioxidant activity from the hot spring cyanobacterial cell‐free extract was not contributed only by the PE, but also came from phenolic compounds and other oxidative substances.     

Environmental controls on microbial colonization of high Arctic cryptoendolithic habitats

Sandstone outcrops around Eureka, Ellesmere Island, Nunavut (80°N) in the Canadian high Arctic are host to abundant cryptoendolithic microbial communities. Continuous measurements over 2 years (2002–2004) of climate and environmental parameters showed that cryptoendolithic habitats experience warmer temperatures and wetter conditions than the exposed rock surface. Subsurface temperature fluctuations were moderated by the thermal capacity of the rock substrate and varied as a function of depth, aspect, and albedo. Rain, snow or snowmelt substantially increased subsurface moisture levels, which persist for significant time periods after initial precipitation events. These conditions produced a habitat amenable to colonization by cyanobacteria, fungi and algae. The dominance of one microbial community over another varied between sites, however these differences existed in habitats with similar temperature conditions. Greater diversity of microorganisms at this Arctic location compared to similar habitats in the Antarctic Dry Valleys is explained by warmer temperatures during summer months that lead to longer periods for both active (∼3,700 h year⁻¹) and ideal (∼2,500 h year⁻¹) calculated metabolic activities as well as abundant moisture in the form of liquid water.Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at .     

The spatial structures of hypolithic communities in the Dry Valleys of East Antarctica

Hypolithic communities represent important reservoirs of microbial life in hyper-arid deserts. A number of studies on the diversity and ecology of these communities from different geographic areas have been reported in the past decade, but the spatial distribution of the different components of these communities is still not understood. Moss- and cyanobacteria-dominated hypolithic community morphotypes from Miers Valley (McMurdo Dry Valleys, East Antarctica) were analyzed by electron microscopy in order to characterize the microscale spatial structure. The two communities showed a high degree of internal organization, but differing according to the biological composition. In moss-dominated hypoliths, the moss plantlets are intermixed with mineral fragments of soil origin. However, in cyanobacteria-dominated hypoliths, a layered spatial organization was structured by filamentous cyanobacteria and associated extracellular polymeric components. While moss cells were lacking in cyanobacteria-dominated communities, biofilms formed by cyanobacteria and heterotrophic bacteria were observed in both community morphotypes. The water-holding capacity of both live and dead moss cells and the associated organic matrix, together with the protective properties of the extracellular polymeric substances, could facilitate the survival and activity of these communities. Similar structural strategies can favor the survival of microbial communities in different extreme environments.     

Origin and Phylogeny of Microbes Living in Permanent Antarctic Lake Ice

Abstract The phylogenetic diversity of bacteria and cyanobacteria colonizing sediment particles in the permanent ice cover of an Antarctic lake was characterized by analyses of 16S rRNA genes amplified from environmental DNA. Samples of mineral particles were collected from a depth of 2.5 m in the 4-m-thick ice cover of Lake Bonney, McMurdo Dry Valleys, Antarctica. A rRNA gene clone library of 198 clones was made and characterized by sequencing and oligonucleotide probe hybridization. The library was dominated by representatives of the cyanobacteria, proteobacteria, and Planctomycetales, but also contained diverse clones representing many other microbial groups, including the Acidobacterium/Holophaga division, the Green Non-Sulfur division, and the Actinobacteria. Six oligonucleotide probes were made for the most abundant clades recovered in the library. To determine whether the ice microbial community might originate from wind dispersal of the algal mats found elsewhere in Taylor Valley, the probes were hybridized to 16S rDNAs amplified from three samples of terrestrial cyanobacterial mats collected at nearby sites, as well as to bacterial 16S rDNAs from the lake ice community. The results demonstrate the presence of a diverse microbial community dominated by cyanobacteria in the lake ice, and also show that the dominant members of the lake ice microbial community are found in terrestrial mats elsewhere in the area. The lake ice microbial community appears to be dominated by organisms that are not uniquely adapted to the lake ice ecosystem, but instead are species that originate elsewhere in the surrounding region and opportunistically colonize the unusual habitat provided by the sediments suspended in lake ice. Received: 16 August 1999; Accepted: 28 December 1999; Online Publication: 28 April 2000     

CYANOBACTERIAL ASSEMBLAGES IN PERMANENT ICE COVERS ON ANTARCTIC LAKES: DISTRIBUTION, GROWTH RATE, AND TEMPERATURE RESPONSE OF PHOTOSYNTHESIS

The proliferation of microalgae in the McMurdo Dry Valleys of Antarctica is intricately linked to the seasonal cycle involving the freezing and melting of water. Anecdotal observations and preliminary sampling have found cyanobacterial cells in ice covers on lakes in the McMurdo Dry Valleys, and several of these ice covers are known to undergo seasonal freeze–thaw cycles. Therefore, we sought to determine the distribution and abundance of cyanobacterial assemblages in several permanent ice covers throughout the McMurdo Dry Valleys and to determine their rates of growth and their photosynthetic physiologies upon encountering liquid water. We found that the majority of the permanent ice covers contained cyanobacterial assemblages in close association with sedimentary material. Cyanobacterial biomass was conspicuously absent in sediment-free ice covers, suggesting that the seasonal interaction between the sediments, ice, and solar radiation present the necessary liquid water environment for cyanobacterial growth. All assemblages exhibited extremely low rates of photosynthesis when first exposed to liquid water. Despite the low rates of photosynthesis, a large proportion (41%) of the photosynthate was incorporated into protein, indicating that the cells were undergoing efficient net cellular growth. The short-term response (24 h) of photosynthesis to a range of temperatures showed optimum rates occurring at temperatures >15° C, which is similar to those of psychrotrophic cyanobacteria isolates from soil and stream habitats, which we believe provides the inoculum for the in- ice habitats.     

Microphytobenthic species composition,pigment concentration,and primary production in sublittoral sediments of the Trondheimsfjord (Norway)1

In spring 2005, monthly sampling was carried out at a sublittoral site near Tautra Island. Microphytobenthic identification, abundance (ABU), and biomass (BIOM), were performed by microscopic analyses. Bacillariophyceae accounted for 67% of the total ABU, and phytoflagellates constituted 30%. The diatom floristic list consisted of 38 genera and 94 species. Intact light‐harvesting pigments chl a, chl c, and fucoxanthin and their derivatives were identified and quantified by HPLC. Photoprotective carotenoids were also observed (only as diadinoxanthin; no diatoxanthin was detected). Average fucoxanthin content was 4.57 ± 0.45 μg fucoxanthin · g sediment dry mass^?1, while the mean chl a concentration was 2.48 ± 0.15 μg · g^?1 dry mass. Both the high fucoxanthin:chl a ratio (considering nondegraded forms) and low amounts of photoprotective carotenoids indicated that the benthic microalgal community was adapted to low light. Microphytobenthic primary production was estimated in situ (MPPs, from 0.15 to 1.28 mg C · m^?2 · h^?1) and in the laboratory (MPPp, from 6.79 to 34.70 mg C · m^?2 · h^?1 under light saturation) as ¹⁴C assimilation; in April it was additionally estimated from O₂‐microelectrode studies (MPP_O2) along with the community respiration. MPP_O2 and the community respiration equaled 22.9 ± 7.0 and 7.4 ± 1.8 mg C · m^?2 · h^?1, respectively. A doubling of BIOM from April to June in parallel with a decreasing photosynthetic activity per unit chl a led us to suggest that the microphytobenthic community was sustained by heterotrophic metabolism during this period.