Seasonal succession and UV sensitivity of marine bacterioplankton at an Antarctic coastal site

Despite extensive microbial biodiversity studies around the globe, studies focusing on diversity and community composition of Bacteria in Antarctic coastal regions are still scarce. Here, we studied the diversity and development of bacterioplankton communities from Prydz Bay (Eastern Antarctic) during spring and early summer 2002-2003. Additionally, we investigated the possible shaping effects of solar UV radiation (UV-R: 280-400 nm) on bacterioplankton communities incubated for 13-14 days in 650-L minicosm tanks. Ribosomal DNA sequence analysis of the natural bacterioplankton communities revealed an initial springtime community composed of three evenly abundant bacterial classes: Cytophaga-Flavobacteria- Bacteroidetes (CFB), Gammaproteobacteria and Alphaproteobacteria. At the end of spring, a shift occurred toward a CFB-dominated community, most likely a response to the onset of a springtime phytoplankton bloom. The tail end of Prydz Bay clone library diversity revealed sequences related to Deltaproteobacteria, Verrucomicrobiales, Planctomycetes, Gemmatimonadetes and an unclassified bacterium (ANT4E12). Minicosm experiments showed that incubation time was the principal determinant of bacterial community composition and that UV-R treatment significantly changed the composition in only two of the four experiments. Thus, the successional maturity of the microbial community in our minicosm studies appears to be a greater determinant of bacterial community composition rather than the nonprofound and subtle effects of UV-R

Shifts in coastal Antarctic marine microbial communities during and after melt water-related surface stratification

Antarctic coastal waters undergo major physical alterations during summer. Increased temperatures induce sea-ice melting and glacial melt water input, leading to strong stratification of the upper water column. We investigated the composition of micro-eukaryotic and bacterial communities in Ryder Bay, Antarctic Peninsula, during and after summertime melt water stratification, applying community fingerprinting (denaturing gradient gel electrophoresis) and sequencing analysis of partial 18S and 16S rRNA genes. Community fingerprinting of the eukaryotic community revealed two major patterns, coinciding with a period of melt water stratification, followed by a period characterized by regular wind-induced breakdown of surface stratification. During the first stratified period, we observed depth-related differences in eukaryotic fingerprints while differences in bacterial fingerprints were weak. Wind-induced breakdown of the melt water layer caused a shift in the eukaryotic community from an Actinocyclus sp.- to a Thalassiosira sp.-dominated community. In addition, a distinct transition in the bacterial community was found, but with a few days' delay, suggesting a response to the changes in the eukaryotic community rather than to the mixing event itself. Sequence analysis revealed a shift from an Alpha- and Gammaproteobacteria to a Cytophaga-Flavobacterium-Bacteroides-dominated community under mixed conditions. Our results show that melt water stratification and the transition to nonstabilized Antarctic surface waters may have an impact not only on micro-eukaryotic but also bacterial community composition

Structure and dynamics of marine bacterioplancton from Potter Cove, Antarctica

En las aguas oceánicas el bacterioplancton marino representan la mayor parte de la biomasa (Granéli y col. 2004), juega un papel clave en el ciclo de nutrientes y constituye un factor importante en el flujo de carbono (Ducklow, 2000). Además en las regiones templadas y polares son fundamentales para las interacciones oceáno-atmosféra y la red trófica oceánica (Prabagaran y col. 2007). En algunas aguas costeras marinas antárticas, como las de Caleta Potter, a pesar de tener un alto nivel de nutrientes no evidencian florecimientos apreciables del fitoplancton en los meses de verano (Schloss y Ferreyra, 2002). Bajo esta condición, el bacterioplancton parece ser el principal responsable de la incorporación de los nutrientes en su biomasa, permitiendo que estén disponibles para los niveles tróficos superiores. Sin embargo hasta el momento no existen trabajos sobre la variación temporal y espacial de la comunidad bacterioplancton en Caleta Potter ubicada en la Isla 25 de Mayo / King George. Shetland del Sur, Antártida. Nuestro trabajo tiene como objetivo el estudio de la estructura y dinámica de bacterioplancton de Caleta Potter. Estudios independiente de cultivo son esenciales para determinar la biodiversidad de comunidades bacterianas marinas, debido a que sólo una pequeña fracción del bacterioplancton puede cultivarse (Amann et al. 1995). Nuestro objetivo fue estudiar, mediante la construcción de bibliotecas de clones del ADNr 16 S, la estructura y variación espacial del bacterioplancton de Caleta Potter en tres zonas con diferente salinidad, así como su dinámica interestacional (entre verano e invierno)

Changes in salinity and temperature drive marine bacterial communities’ structure at Potter Cove, Antarctica

Coastal areas of the West Antarctic Peninsula (WAP) constitute a rich and biodiverse marine zone. Despite these ecosystems being supported by the microorganism’s activity, the structure of microbial communities is insufficiently studied. As WAP is the area most affected by global warming worldwide, the increased glacier melting caused by the global warming and the consequent increase of the water runoff could be deeply affecting these microbial communities. To advance knowledge about the structure of microbial communities and its response to the environmental factors, a full-year study of marine bacterioplankton was conducted at Potter Cove, Antarctica. Multivariate analysis based on denaturing gradient gel electrophoresis (DGGE) and environmental data revealed a seasonal pattern in the structure of the bacterioplankton community, with spring–summer clustering separately from autumn–winter samples. Salinity, temperature and particulated matter were the main environmental driving forces. Based on the seasonal patterns, five bacterial clone libraries were performed from three sampling sites (E1, inner cove; E2, outer cove; and E3, mouth of a creek). Phylogenetic analysis of libraries generated 301 operational taxonomic units (OTUs), revealing the enormous richness and high diversity of these communities. Proteobacteria (68%), Bacteroidetes (20%) and Actinobacteria (8%) were the most represented phyla. During summer, bacterial community from E1 resembled that observed in E3, whereas during winter it resembled the E2 community. Results evidenced the influence of glacial meltwater input and showed the high variability of the bacterioplankton from inner cove. This study contributes to the better understanding of the structure of the Potter Cove marine ecosystems and could be reflecting the behavior of other similar ecosystems from WAP

Diversity and dynamics of Antarctic marine microbial eukaryotes under manipulated environmental UV radiation

In the light of the predicted global climate change, it is essential that the status and diversity of polar microbial communities is described and understood. In the present study, molecular tools were used to investigate the marine eukaryotic communities of Prydz Bay, Eastern Antarctica, from November 2002 to January 2003. Additionally, we conducted four series of minicosm experiments, where natural Prydz Bay communities were incubated under six different irradiation regimes, in order to investigate the effects of natural UV radiation on marine microbial eukaryotes. Denaturing gradient gel electrophoresis (DGGE) and 18S rRNA gene sequencing revealed a eukaryotic Shannon diversity index averaging 2.26 and 2.12, respectively. Phylogenetic analysis of 472 sequenced clones revealed 47 phylotypes, belonging to the Dinophyceae, Stramenopiles, Choanoflagellidae, Ciliophora, Cercozoa and Metazoa. Throughout the studied period, three communities were distinguished: a postwinter/early spring community comprising dinoflagellates, ciliates, cercozoans, stramenopiles, viridiplantae, haptophytes and metazoans; a dinoflagellate-dominated community; and a diatom-dominated community that developed after sea ice breakup. DGGE analysis showed that size fraction and time had a strong shaping effect on the community composition; however, a significant contribution of natural UV irradiance towards microeukaryotic community composition could not be detected. Overall, dinoflagellates dominated our samples and their diversity suggests that they fulfill an important role in Antarctic coastal marine ecosystems preceding ice breakup as well as between phytoplankton bloom events

Marine archaeal community structure from Potter Cove, Antarctica:high temporal and spatial dominance of the phylum Thaumarchaeota

Archaeal communities represent a significant fraction of the Antarctic marine microbial plankton and surely play a relevant role in the proper functioning of the ecosystem. We studied the archaeal community structure in surface water samples from Potter Cove, Antarctica. Temporal and spatial variability was investigated along a whole year cycle using DGGE and 16S rRNA gene sequencing from clone libraries. Additionally, photosynthetic pigments, suspended particulate matter (SPM), salinity and temperature were measured. The multivariate analysis performed using diversity, dominance and richness indexes, and environmental data evidenced a seasonal pattern in the archaeal community and revealed that spring–summer samples clustered separately from autumn to winter ones. High salinity and high values of diversity and richness were related to autumn–winter samples, whereas the spring–summer samples were associated mainly with higher values of temperature, SPM, Chl-a, carotenoids and archaeal dominance. The phylogenetic analysis of five independent clone libraries (467 sequences) showed that 448 sequences fell into a clade containing Nitrosopumilus maritimus and other sequences of ammonia-oxidizing archaea which belong to the Thaumarchaeota phylum. A high fraction of these sequences (62 %) constituted a single cluster containing only highly similar Potter Cove representatives, which probably belong to the same species. Fifteen sequences were affiliated to a group closely related to the order Thermoplasmatales (Euryarchaeota). This work represents a first step towards obtaining a deep understanding of the structure of archaeal communities from Antarctic coastal marine environments and contributes to cover the current gap in knowledge of the dynamics of the archaeoplankton in the Antarctic seas