Cyanobacterial Sequences Research Articles

Environmental conditions play a key role in controlling the composition and diversity of Colombian biocrust microbiomes.

Drylands soils worldwide are naturally colonized by microbial communities known as biocrusts. These soil microbiomes render important ecosystem services associated with soil fertility, water holding capacity, and stability to the areas they cover. Because of the importance of biocrusts in the global cycling of nutrients, there is a growing interest in describing the many microbial configurations these communities display worldwide. However, comprehensive 16S rRNA genes surveys of biocrust communities do not exist for much of the planet: for example, in the continents of South America and the northern part of Africa. The absence of a global understanding of biocrust biodiversity has lead us to assign a general importance to community members that may, in fact, be regional. Here we report for the first time the presence of biocrusts in Colombia (South America) through 16S rRNA genes surveys across an arid, a semi-arid and a dry subtropical region within the country. Our results constitute the first glance of the Bacterial/Archaeal communities associated with South American biocrust microbiomes. Communities where cyanobacteria other than Microcoleus vaginatus prevail, despite the latter being considered a key species elsewhere, illustrate differentiable results in these surveys. We also find that the coastal biocrust communities in Colombia include halo-tolerant and halophilic species, and that niche preference of some nitrogen fixing organisms deviate from previously described global trends. In addition, we identified a high proportion (ranging from 5 to 70%, in average) of cyanobacterial sequences that did not match any formally described cyanobacterial species. Our investigation of Colombian biocrusts points to highly diverse communities with climatic regions controlling taxonomic configurations. They also highlight an extensive local diversity to be discovered which is central to better design management and restoration strategies for drylands soils currently undergoing disturbances due to land use and global warming. Finally, this field study highlights the need for an improved mechanistic understanding of the response of key biocrust community members to changes in moisture and temperature.

Identification of potential microbial risk factors associated with fecal indicator exceedances at recreational beaches

BackgroundFecal bacterial densities are proxy indicators of beach water quality, and beach posting decisions are made based on Beach Action Value (BAV) exceedances for a beach. However, these traditional beach monitoring methods do not reflect the full extent of microbial water quality changes associated with BAV exceedances at recreational beaches (including harmful cyanobacteria). This proof of concept study evaluates the potential of metagenomics for comprehensively assessing bacterial community changes associated with BAV exceedances compared to non-exceedances for two urban beaches and their adjacent river water sources.ResultsCompared to non-exceedance samples, BAV exceedance samples exhibited higher alpha diversity (diversity within the sample) that could be further differentiated into separate clusters (Beta-diversity). For Beach A, Cyanobacterial sequences (resolved as Microcystis and Pseudanabaena at genus level) were significantly more abundant in BAV non-exceedance samples. qPCR validation supported the Cyanobacterial abundance results from metagenomic analysis and also identified saxitoxin genes in 50% of the non-exceedance samples. Microcystis sp and saxitoxin gene sequences were more abundant on non-exceedance beach days (when fecal indicator data indicated the beach should be open for water recreational purposes). For BAV exceedance days, Fibrobacteres, Pseudomonas, Acinetobacter, and Clostridium sequences were significantly more abundant (and positively correlated with fecal indicator densities) for Beach A. For Beach B, Spirochaetes (resolved as Leptospira on genus level) Burkholderia and Vibrio sequences were significantly more abundant in BAV exceedance samples. Similar bacterial diversity and abundance trends were observed for river water sources compared to their associated beaches. Antibiotic Resistance Genes (ARGs) were also consistently detected at both beaches. However, we did not observe a significant difference or correlation in ARGs abundance between BAV exceedance and non-exceedance samples.ConclusionThis study provides a more comprehensive analysis of bacterial community changes associated with BAV exceedances for recreational freshwater beaches. While there were increases in bacterial diversity and some taxa of potential human health concern associated with increased fecal indicator densities and BAV exceedances (e.g. Pseudomonas), metagenomics analyses also identified other taxa of potential human health concern (e.g. Microcystis) associated with lower fecal indicator densities and BAV non-exceedances days. This study can help develop more targeted beach monitoring strategies and beach-specific risk management approaches.

Influence of sedimentary deposition on the microbial assembly process in Arctic Holocene marine sediments.

The sea-level rise during the Holocene (11-0 ky BP) and its resulting sedimentation and biogeochemical processes may control microbial life in Arctic sediments. To gain further insight into this interaction, we investigated a sediment core (up to 10.7 m below the seafloor) from the Chuckchi Shelf of the western Arctic Ocean using metabarcoding-based sequencing and qPCR to characterize archaeal and bacterial 16S rRNA gene composition and abundance, respectively. We found that Arctic Holocene sediments harbor local microbial communities, reflecting geochemical and paleoclimate separations. The composition of bacterial communities was more diverse than that of archaeal communities, and specifically distinct at the boundary layer of the sulfate-methane transition zone. Enriched cyanobacterial sequences in the Arctic middle Holocene (8-7 ky BP) methanogenic sediments remarkably suggest past cyanobacterial blooms. Bacterial communities were phylogenetically influenced by interactions between dispersal limitation and environmental selection governing community assembly under past oceanographic changes. The relative influence of stochastic and deterministic processes on the bacterial assemblage was primarily determined by dispersal limitation. We have summarized our findings in a conceptual model that revealed how changes in paleoclimate phases cause shifts in ecological succession and the assembly process. In this ecological model, dispersal limitation is an important driving force for progressive succession for bacterial community assembly processes on a geological timescale in the western Arctic Ocean. This enabled a better understanding of the ecological processes that drive the assembly of communities in Holocene sedimentary habitats affected by sea-level rise, such as in the shallow western Arctic shelves.

Salinity matters the most: How environmental factors shape the diversity and structure of cyanobacterial mat communities in high altitude arid ecosystems.

Microbial mats are complex communities of benthic microorganisms that occur at the soil-water interphase in lakes' shores, streams, and ponds. In the cold, mountainous desert of Eastern Pamir (Tajikistan), where scarce water bodies are influenced by extreme environmental conditions, photosynthetic cyanobacteria form diverse mats. The mats are characterized by different morphology and thickness. Their habitats exhibit a wide range of conditions; from oligosaline to hypersaline, oligotrophic to hypertrophic, and from cold ponds to hot springs. The aim of the present study was to reveal the taxonomic composition and structure of these mats and to examine which environmental factors influence them. Fifty-one mats were collected from small water bodies around Bulunkul, Karakul, and Rangkul Lakes in 2015 and 2017. The physical and chemical properties of the water were measured in situ, while the concentration of nutrients was analyzed ex-situ. To reveal the taxonomic composition of the mats, the hypervariable V3-V4 region of the 16S rRNA gene was examined using NGS technology. The results of bioinformatic analyses were compared with microscopic observations. They showed that Cyanobacteria was the dominant phylum, constituting on average 35% of bacterial ASVs, followed by Proteobacteria (28%), Bacteroidota (11%), and Firmicutes (9%). Synechococcales, Oscillatoriales, and Nostocales orders prevailed in Oxyphotobacteria, with a low contribution of Chroococcales, Gloeobacterales, and Chroococcidiopsidales. Occasionally the non-photosynthetic Vampirivibrionia (Melainabacteria) and Sericytochromatia from sister clades to Oxyphotobacteria were noted in the samples. Moreover, there was a high percentage of unidentified cyanobacterial sequences, as well as the recently described Hillbrichtia pamiria gen. et sp. nov., present in one of the samples. Salinity, followed by Na and K concentrations, correlated positively with the composition and structure of Oxyphotobacteria on different taxonomic levels and the abundance of all bacterial ASVs. The study suggests that the investigated communities possibly host more novel and endemic species. Among the environmental factors, salinity influenced the Oxyphotobacteria communities the most. Overall, the microenvironmental factors, i.e. the conditions in each of the reservoirs seemed to have a larger impact on the diversity of microbial mats in Pamir than the "subregional" factors, related to altitude, mean annual air temperature and distance between these subregions.

Cyanobacteria and Algae Meet at the Limits of Their Habitat Ranges in Moderately Acidic Hot Springs

AbstractMicrobial oxygenic photosynthesis in thermal habitats is thought to be performed by Bacteria in circumneutral to alkaline systems (pH > 6) and by Eukarya in acidic systems (pH < 3), yet the predominant oxygenic phototrophs in thermal environments with pH values intermediate to these extremes have received little attention. Sequencing of 16S and 18S rRNA genes was performed on samples from twelve hot springs in Yellowstone National Park (Wyoming, USA) with pH values from 3.0 to 5.5, revealing that Cyanobacteria of the genus Chlorogloeopsis and algae of the genus Cyanidioschyzon (phylum Rhodophyta) coexisted in ten of these springs. Cyanobacterial 16S rRNA genes were more abundant than rhodophyte 18S rRNA genes by 1–7 orders of magnitude, with rhodophyte template abundance approaching that of Cyanobacteria only at the most acidic sites. The ketocarotenoids echinenone and canthaxanthin were identified in samples from all but one spring yielding cyanobacterial sequences and are attributed to pigment synthesis by Cyanobacteria, whereas the absence of detectable chloroplast sequences affiliated with Cyanidioschyzon, pH and temperatures in excess of its limits for growth, and other observations collectively suggested these algae were inactive in many of the springs at the time of sampling. Fluctuations in the supply of meteoric water likely contribute to physicochemical variability in these springs, leading to transitions in microbial community composition. Spatial overlap, but perhaps not temporal overlap, in the habitat ranges of bacterial and eukaryal oxygenic phototrophs indicates that the notion of a sharp transition between these lineages with respect to pH is unwarranted.

Seasonal Dynamics of Epiphytic Microbial Communities on Marine Macrophyte Surfaces.

Surfaces of marine macrophytes are inhabited by diverse microbial communities. Most studies focusing on epiphytic communities of macrophytes did not take into account temporal changes or applied low sampling frequency approaches. The seasonal dynamics of epiphytic microbial communities was determined in a meadow of Cymodocea nodosa invaded by Caulerpa cylindracea and in a monospecific settlement of C. cylindracea at monthly intervals. For comparison the ambient prokaryotic picoplankton community was also characterized. At the OTU level, the microbial community composition differed between the ambient water and the epiphytic communities exhibiting host-specificity. Also, successional changes were observed connected to the macrophyte growth cycle. Taxonomic analysis, however, showed similar high rank taxa (phyla and classes) in the ambient water and the epiphytic communities, with the exception of Desulfobacterota, which were only found on C. cylindracea. Cyanobacteria showed seasonal changes while other high rank taxa were present throughout the year. In months of high Cyanobacteria presence the majority of cyanobacterial sequences were classified as Pleurocapsa. Phylogenetic groups present throughout the year (e.g., Saprospiraceae, Rhodobacteraceae, members without known relatives within Gammaproteobacteria, Desulfatitalea, and members without known relatives within Desulfocapsaceae) constituted most of the sequences, while less abundant taxa showed seasonal patterns connected to the macrophyte growth cycle. Taken together, epiphytic microbial communities of the seagrass C. nodosa and the macroalga C. cylindracea appear to be host-specific and contain taxa that undergo successional changes.

Coleofasciculaceae, a Monophyletic Home for the Microcoleus steenstrupii Complex and Other Desiccation-tolerant Filamentous Cyanobacteria.

Cyanobacteria classified as Microcoleus steenstrupii play a significant role as pioneers of biological soil crusts (biocrusts), but this taxon is recognized to constitute a diverse complex of strains and field populations. With the aim of clarifying its systematics, we conducted a polyphasic characterization of this and allied taxa. A 16S ribosomal gene meta-analysis of published environmental sequences showed that the complex encompasses a variety of well supported genus-level clades with clade-specific environmental preferences, indicating significant niche differentiation. Fifteen strains in the M. steenstrupii complex were selected as representative of naturally occurring clades and studied using 16S rRNA gene phylogeny, morphology, and niche delineation with respect to temperature and rainfall. Bayesian phylogenetic reconstructions within a comprehensive, curated database of long 16S rRNA cyanobacterial sequences (1,000 base pairs or more) showed that they all belonged in a monophyletic, family-level clade (91.4% similarity) that included some other known genera of desiccation-resistant, largely terrestrial, filamentous, nonheterocystous cyanobacteria, including Coleofasciculus, the type genus for the family Coleofasciculaceae. To accommodate this biodiversity, we redescribe the Coleofasciculaceae, now composed of 11 genera, among which six are newly described herein (Funiculus, Parifilum, Arizonema, Crassifilum, Crustifilum, and Allocoleopsis), and five were previously recognized (Porphyrosiphon, Coleofasciculus, Pycnacronema, Potamolinea, and Wilmottia). We provide an evaluation of their respective niches and global distributions within biocrusts based on published molecular data. This new systematics treatment should help simplify and improve our understanding of the biology of terrestrial cyanobacteria.

A distinct molecular signature on anhydrobiotic cyanobacterial metallothioneins

Anhydrobiosis refers to a state of suspended animation in which some organisms enter when exposed to extreme desiccation, ensuring them an outstanding tolerance to several physical stresses due to molecular and cellular adaptations. Metallothioneins (MTs) are short cysteine-rich metal-chelating proteins that work as a cellular protection element in metal ion-rich conditions. Here we aimed to investigate possible molecular signatures in primary and tertiary structures in anhydrobiotic cyanobacterial MTs. Anhydrobiotic and non-anhydrobiotic cyanobacterial MT amino acid sequences were retrieved from NCBI database and aligned in Clustal Omega server. Additionally, the amino acid compositions of these sequences were determined by GeneRunner. Further, we carried out homology-modeling via SWISS-MODEL, structural superposition in UCSF Chimera 1.4 Matchmaker tool and ligand-binding site prediction via COFACTOR. In silico analyses revealed specific divergences in amino acid positions between MT groups, evidencing positive and negative selections, however without affecting final protein structures. Some of these changes on polypeptide sequence potentially enhance protein stabilization during desiccation, whereas others possibly act as additional metal-ion coordinating residues. Analyses on the molecular adaptations on anhydrobiotic cyanobacterial MTs help shed light on their molecular functions and biological roles, as well as may have applications on the development of desiccation- and metal-tolerant organisms.

Diversity and distribution of nitrogen fixation genes in the oxygen minimum zones of the world oceans

Abstract. Diversity and community composition of nitrogen (N) fixing microbes in the three main oxygen minimum zones (OMZs) of the world ocean were investigated using operational taxonomic unit (OTU) analysis of nifH clone libraries. Representatives of three of the four main clusters of nifH genes were detected. Cluster I sequences were most diverse in the surface waters, and the most abundant OTUs were affiliated with Alpha- and Gammaproteobacteria. Cluster II, III, and IV assemblages were most diverse at oxygen-depleted depths, and none of the sequences were closely related to sequences from cultivated organisms. The OTUs were biogeographically distinct for the most part – there was little overlap among regions, between depths, or between cDNA and DNA. In this study of all three OMZ regions, as well as from the few other published reports from individual OMZ sites, the dominance of a few OTUs was commonly observed. This pattern suggests the dynamic response of the components of the overall diverse assemblage to variable environmental conditions. Community composition in most samples was not clearly explained by environmental factors, but the most abundant OTUs were differentially correlated with the obvious variables, temperature, salinity, oxygen, and nitrite concentrations. Only a few cyanobacterial sequences were detected. The prevalence and diversity of microbes that harbor nifH genes in the OMZ regions, where low rates of N fixation are reported, remains an enigma.

Extensive photobiont sharing in a rapidly radiating cyanolichen clade.

Recent studies have uncovered remarkable diversity in Dictyonema s.lat. basidiolichens, here recognized as subtribe Dictyonemateae. This group includes five genera and 148 species, but hundreds more await description. The photobionts of these lichens belong to Rhizonema, a recently resurrected cyanobacterial genus known by a single species. To further investigate photobiont diversity within Dictyonemateae, we generated 765 new cyanobacterial sequences from 635 specimens collected from 18 countries. The ITS barcoding locus supported the recognition of 200 mycobiont (fungal) species among these samples, but the photobiont diversity was comparatively low. Our analyses revealed three main divisions of Rhizonema, with two repeatedly recovered as monophyletic (proposed as new species), and the third mostly paraphyletic. The paraphyletic lineage corresponds to R.interruptum and partnered with mycobionts from all five genera in Dictyonemateae. There was no evidence of photobiont-mycobiont co-speciation, but one of the monophyletic lineages of Rhizonema appears to partner predominantly with one of the two major clades of Cora (mycobiont) with samples collected largely from the northern Andes. Molecular clock estimations indicate the Rhizonema species are much older than the fungal species in the Dictyonemateae, suggesting that these basidiolichens obtained their photobionts from older ascolichen lineages and the photobiont variation in extant lineages of Dictyonemateae is the result of multiple photobiont switches. These results support the hypothesis of lichens representing "fungal farmers," in which diverse mycobiont lineages associate with a substantially lower diversity of photobionts by sharing those photobionts best suited for the lichen symbiosis among multiple and often unrelated mycobiont lineages.

Weak Influence of Paleoenvironmental Conditions on the Subsurface Biosphere of Lake Ohrid over the Last 515 ka.

Lacustrine sediments are widely used to investigate the impact of climatic change on biogeochemical cycling. In these sediments, subsurface microbial communities are major actors of this cycling but can also affect the sedimentary record and overprint the original paleoenvironmental signal. We therefore investigated the subsurface microbial communities of the oldest lake in Europe, Lake Ohrid (North Macedonia, Albania), to assess the potential connection between microbial diversity and past environmental change using 16S rRNA gene sequences. Along the upper ca. 200 m of the DEEP site sediment record spanning ca. 515 thousand years (ka), our results show that Atribacteria, Bathyarchaeia and Gammaproteobacteria structured the community independently from each other. Except for the latter, these taxa are common in deep lacustrine and marine sediments due to their metabolic versatility adapted to low energy environments. Gammaproteobacteria were often co-occurring with cyanobacterial sequences or soil-related OTUs suggesting preservation of ancient DNA from the water column or catchment back to at least 340 ka, particularly in dry glacial intervals. We found significant environmental parameters influencing the overall microbial community distribution, but no strong relationship with given phylotypes and paleoclimatic signals or sediment age. Our results support a weak recording of early diagenetic processes and their actors by bulk prokaryotic sedimentary DNA in Lake Ohrid, replaced by specialized low-energy clades of the deep biosphere and a marked imprint of erosional processes on the subsurface DNA pool of Lake Ohrid.

Preliminary Assessment of Microbial Community Structure of Wind-Tidal Flats in the Laguna Madre, Texas, USA.

Aside from two samples collected nearly 50 years ago, little is known about the microbial composition of wind tidal flats in the hypersaline Laguna Madre, Texas. These mats account for ~42% of the lagoon’s area. These microbial communities were sampled at four locations that historically had mats in the Laguna Madre, including Laguna Madre Field Station (LMFS), Nighthawk Bay (NH), and two locations in Kenedy Ranch (KRN and KRS). Amplicon sequencing of 16S genes determined the presence of 51 prokaryotic phyla dominated by Bacteroidota, Chloroflexi, Cyanobacteria, Desulfobacteria, Firmicutes, Halobacteria, and Proteobacteria. The microbial community structure of NH and KR is significantly different to LMFS, in which Bacteroidota and Proteobacteria were most abundant. Twenty-three cyanobacterial taxa were identified via genomic analysis, whereas 45 cyanobacterial taxa were identified using morphological analysis, containing large filamentous forms on the surface, and smaller, motile filamentous and coccoid forms in subsurface mat layers. Sample sites were dominated by species in Oscillatoriaceae (i.e., Lyngbya) and Coleofasciculaceae (i.e., Coleofasciculus). Most cyanobacterial sequences (~35%) could not be assigned to any established taxa at the family/genus level, given the limited knowledge of hypersaline cyanobacteria. A total of 73 cyanobacterial bioactive metabolites were identified using ultra performance liquid chromatography-Orbitrap MS analysis from these commu nities. Laguna Madre seems unique compared to other sabkhas in terms of its microbiology.

Analysis of Marine Planktonic Cyanobacterial Assemblages From Mooriganga Estuary, Indian Sundarbans Using Molecular Approaches

The ecological significance of marine planktonic cyanobacteria in mangrove ecosystems is not well understood from the context of community structure and function. In this study, members of the marine planktonic cyanobacterial communities were elucidated based on 16S rRNA sequencing (clone libraries and Illumina sequencing) and microscopic approaches from the Sundarbans Biological Observatory Time Series (SBOTS) stations Stn1 and Stn 3 located in Mooriganga estuary over six months representing monsoon and post-monsoon seasons of 2012. In total 222 sequences were marine planktonic cyanobacteria-like and were dominated by three major clades of Synechococcus-like 16S rRNA sequences (160 sequences). There was clear dominance of Synechococcus sp. KORDI-78 like sequences (71 sequences) in both monsoon and post-monsoon seasons from the study area. Although in very low numbers, other cyanobacterial sequences showing taxonomic affiliation with members of Chroococcales, Pleurocapsales, Oscillatoriales and Stigonematales were also encountered. The presence of some of the representative genera belonging to the above Orders were reconfirmed by bright field microscopy from both stations of SBOTS. Presence of four novel clades of planktonic cyanobacteria were also confirmed from the study area based on molecular phylogeny thereby indicating unexplored cyanobacterial diversity is high in Sundarbans. Illumina sequencing undertaken for both stations of SBOTS in one of the monsoon months of 2014 (July) revealed low abundance of cyanobacteria-like sequences (2349 out of 4276863 pair-end reads) and dominance of KORDI-78 like sequences. Principal component analysis showed that dissolved nutrients, transparency and salinity influenced the observed marine planktonic cyanobacterial assemblages of Sundarbans. There was overall dominance of Synechococccus-like 16S rRNA sequences confirming the importance of small-sized picocyanobacteria cells and their ecological importance in export of carbon in mangrove ecosystems.

Bacterial Community Composition of Sapanca Lake During a Cyanobacterial Bloom

Microbial community compositions and functions of freshwater ecosystems vary due to the environmental parameters and water chemistry. Transient bloom events play a crucial role on the community profiles. In this study, a specific focus was set to provide a snapshot of the bacterial community composition in Lake Sapanca, associated with cyanobacterial bloom by high throughput sequencing method. For this purpose, a sample was collected in the shore of Lake Sapanca during a cyanobacterial bloom, and the bacterial community profile was examined by 16S rRNA amplicon sequencing using the Illumina MiSeq platform. Cyanobacteria represented 94% of the all reads. The bacterial community was re-calculated to evaluate the bacterial diversity in detail by filtering cyanobacterial sequences. The community was dominated by Proteobacteria (44%) and Bacteroidetes (33%) species which are abundant in freshwater ecosystems having an ability to degrade complex organics. Among the classified genera, Flavobacterium and Rheinheimera dominated the bacterial community suggesting a strong link between those species and the cyanobacterial bloom. The experimental work presented here provides one of the first investigations of total bacterial communities in Lake Sapanca by the high throughput sequencing method. Further work is needed with more sampling points and time series to fully understand the bacterial diversity and dynamics.

Metabarcoding reveals a more complex cyanobacterial community than morphological identification

Abstract Next generation sequencing has become a popular method to identify cyanobacterial diversity in ecosystems. Morphological identification poses challenges in deciphering cyanobacterial diversity because phenotypic variations can be misleading, picocyanobacteria are ignored easily, specialists familiar with classification systems are lacking, and updates of taxonomic treatises are not shared in a timely manner or adopted by researchers engaged in monitoring of phytoplankton. In this study, metabarcoding of 54 samples from 7 freshwater systems yielded saturated cyanobacterial sequences, and the compositions of the resulting communities were compared with a dataset generated by morphological identification. A total of 69 cyanobacterial operational taxonomic units (OTUs) were finally codetermined through the ribosomal database project (RDP) via the Silva database and blast analysis using a database maintained by the National Center for Biotechnology Information (NCBI). Blast resolved more OTUs, with 1 and 27 OTUs identified at the species level and 35 and 9 OTUs identified at the genus levels through Silva and NCBI, respectively. Only 13 OTUs were matched at genus levels by these two methods. The accuracy of blast was further verified through molecular phylogeny. Blast results were compared with morphological identification at the genus level. Each method identified 26 genera, and 12 genera were shared by both methods. Half of the genera only identified by metabarcoding have been described recently, and data on morphologically diagnostic characters were not available. Some genera shared morphological similarities, which led them to be misidentified. Ten of the 12 genera found by both methods yielded less than 2 morphological mismatches. These genera produced a higher proportion of occurrences in metabarcoding, which was indicative of higher sensitivity to cyanobacteria. A larger number of species were found in metabarcoding (8–38 OTUs) than in morphological surveys (1–16 morphospecies), nevertheless, the results were positively correlated (R2 = 0.56, p

Community dynamics and function of algae and bacteria during winter in central European great lakes

Abundant phytoplankton and bacteria were identified by microscopy and high-throughput 16S rRNA tag Illumina sequencing of samples from water- and ice phases collected during winter at two central European Great Lakes, Balaton and Fertő (Neusiedlersee). Bacterial reads at all sites were dominated (>85%) by Bacteroidetes and Proteobacteria. Amongst phototrophs, microscopy and 16S sequencing revealed that both phytoplankton and cyanobacteria were represented, with a median of 1500 cyanobacterial sequence reads amongst 13 samples analyzed. The sequence analysis compared replicate Balaton and Fertő ice and water samples with an outgroup from three Hungarian soda lakes. In particular, both water and ice from Fertő contained high contributions from cyanobacteria. Two percent of total reads identified to the level of family in water at Fertő were dominated by a single operational taxonomic unit (OTU) of a cyanobacterium within the Rivulariaceae, which was largely absent from ice. Conversely, ice samples from both lakes yielded an abundant OTU assigned to a Flavobacterium sp. known to be associated with freshwater ice. Principal Coordinates Analysis (PCoA) revealed that the ice communities from all sites were similar to one another, and that the water communities did not cluster together. Fluorescence emission spectra obtained at 77 K confirmed the presence of intact cyanobacteria in Fertő water and ice. Photosynthetic characterization of phototrophs resident in water and ice analyzed by assay of acid-stable photosynthetic H14CO3– incorporation showed that communities from both phases were photosynthetically active, thus adding to growing recognition of ice-covered lakes as viable habitat for phototrophs.

Growth of cyanobacterial soil crusts during diurnal freeze-thaw cycles.

Various Nostoc spp. and related cyanobacteria are able to survive extreme temperatures and are among the most successful colonists of high-elevation sites being exposed due to glacial retreat. It is unclear, however, if cyanobacteria can grow during the extreme freeze-thaw cycles that occur on a year-round basis at high-elevation, peri-glacial sites or if they only grow during the rare periods when freeze-thaw cycles do not occur. We conducted several experiments to determine if cyanobacteria that form biological soil crusts (BSCs) at high-elevation sites (> 5,000 m.a.s.l.) in the Andes can grow during diurnal freeze-thaw cycles on a par with those that occur in the field. Here we show that a soil crust that had been frozen at -20°C for five years was able to increase from 40% to 100% soil coverage during a 45-day incubation during which the soil temperature cycled between -12°C and 26°C every day. In a second, experiment an undeveloped soil with no visible BSCs showed a statistically significant shift in the bacterial community from one containing few cyanobacterial sequences (8% of sequences) to one dominated (27%) by Nostoc, Microcoleus, and Leptolyngbya phylotypes during a 77-day incubation with daily freeze-thaw cycles. In addition, counts of spherical Nostoc-like colonies increased significantly on the soil surface during the experiment, especially in microcosms receiving phosphorus. Taken together these results show that freeze-thaw cycles alone do not limit the growth of BSCs in high-elevation soils, and provide new insight into how life is able to thrive in one of the most extreme terrestrial environments on Earth.

<p><strong><em>Potamosiphon australiensis</em> <em>gen. nov.</em>, <em>sp nov.</em> (Oscillatoriales), a new filamentous cyanobacterium from subtropical north-eastern Australia</strong></p>

A new filamentous cyanobacterium, Potamosiphon australiensis gen. et sp. nov., was isolated from a small coastal stream in subtropical north-eastern Australia, and characterised using combined morphological and phylogenetic attributes. It was found growing on the benthos of Fat Hen Creek amongst cobbles, gravel and large woody debris, mostly as single straight or variously flexuous filaments amongst other algae, but occasionally formed loose aggregations amongst littoral vegetation. Morphologically, Potamosiphon is most similar to members of the genus Lyngbya. Filaments were isopolar, cylindrical, not or slightly constricted at the cross walls. Vegetative cells were discoid, broader than long with finely granular contents, aerotopes were not present. Apical cells were rounded, without calyptra or a thickened outer cell wall. Reproduction occurred via motile hormogonia, which formed often in series, after the occurrence of necridic cells. Trichome fragmentation also occurred following a diagonal division. Following this division trichomes often continued to grow past each other within a common sheath. Thylakoids were irregularly arranged throughout the whole cell volume. Phylogenetic analyses using partial 16S rRNA sequences obtained from three strains of P. australiensis showed that it formed a well supported monophyletic clade, sharing less than 94% nucleotide similarity with other cyanobacterial sequences, including putatively related taxa within the Oscillatoriaceae. It also formed a novel clade in the nifH phylogeny, which was associated with the genus Microseira G.B. McGregor & Sendall.

Microbial Epiphytes of Deep-Water Moss in Crater Lake, Oregon

We characterized the microbes that are attached to deep-water moss in Crater Lake, Oregon. Moss leaves are densely colonized with a microbial community that differs from that found in the water column. Most notably, the cyanobacterial epiphytes on Crater Lake's moss are absent from the water column. Algal and cyanobacterial moss epiphytes were surveyed and identified using microscopy and gene sequencing. We found that diatoms and filamentous algae took up the greatest surface area on moss, with cyanobacterial epiphytes present in fewer numbers. Heterotrophic bacteria were more abundant on moss leaves than eukaryotes but occupied far less surface area. Eukaryotic large subunit rRNA gene sequences obtained from moss DNA extracts verified the presence of several different genera of algae associated with moss. In addition, sequence analysis revealed the presence of symbiotic fungi and protozoa. To identify prokaryotic nitrogen fixers on moss, nitrogenase and nitrogenase-like gene sequences were obtained from moss epiphytes. All of the nitrogenase genes associated with moss epiphytes were cyanobacterial sequences. In contrast, no nitrogenase sequences were detected in the water column. In addition, we cultured and identified four different genera of cyanobacteria from Crater Lake moss leaves. Given that Crater Lake has virtually undetectable levels of nitrate in the zone where moss grows most abundantly, the nitrogen fixing ability of cyanobacterial epiphytes is likely to provide a growth advantage to cyanobacteria and to nearby organisms.

Core bacterial community composition of a cryptoendolithic ecosystem in the Grand Staircase-Escalante National Monument, Utah.

Cryptoendolithic bacterial communities in the Jurassic Navajo Sandstones play an important ecological role in this ecosystem. Developing a better understanding of the role of these cryptoendolithic communities required a deeper knowledge of the microbial diversity present. We analyzed the bacterial diversity in eight sandstones samples from several microgeological features associated with a large sandstone dome. Cryptoendolithic bacterial diversity is clustered into three distinct groups which correlated with topography, suggesting the duration of water retention might be a factor. Comparisons of diversity between each cluster showed that a core bacterial community exists in this habitat. The overall bacterial community structure was dominated by Cyanobacteria, Proteobacteria, Bacteroidetes, and Actinobacteria. The most prevalent genera in cyanobacteria were Leptolyngbya, Chroococcidiopsis, and unclassified cyanobacteria accounting for the bulk of cyanobacterial sequences. Within the Proteobacteria, Alphaproteobacteria were the largest class detected, with members of the Acetobacteraceae, particularly the genus Acidiphilium, being the most abundant. Acidiphilium spp. are capable of aerobic ferric iron reduction under moderately acidic conditions, explaining the high levels of iron (II) in this system. This study highlights the extent of unexplored bacterial diversity in this habitat system and sets the premise for elaborating on the ecological function of cryptoendolithic communities.