No abstract

No abstract

It was once a long-held view that the Antarctic was a pristine environment with low biomass, low biodiversity and low rates of microbial activity. However, as the intensity of scientific investigation has increased, so these views have started to change. In particular, the role and impact of human activity toward indigenous microbial communities has started to come under more intense scrutiny. During the Subglacial Lake Ellsworth exploration campaign in December 2012, a microbiological survey was conducted to determine the extent and likelihood of exogenous input into the subglacial lake system during the hot-water drilling process. Snow was collected from the surface to represent that used for melt water production for hot-water drilling. The results of this study showed that snow used to provide melt water differed in its microbiological composition from that of the surrounding area and raised the question of how the biogeography of snow-borne microorganisms might influence the potential outcome of scientific analyses. In this study, we investigated the biogeography of microorganisms in snow around a series of Antarctic logistic hubs, where human activity was clearly apparent, and from which scientific investigations have been undertaken. A change in microbial community structure with geographical location was apparent and, notably, a decrease in alpha diversity at more remote southern latitudes. Soil-related microorganisms dominated microbial assemblages suggesting terrestrial input, most likely from long-range aeolian transport into continental Antarctica. We also observed that relic DNA was not a major issue when assessing snow samples. Overall, our observations might have profound implications for future scientific activities in Antarctica, such as the need to establish “no-go” protected areas, the need for better characterization of field sites and improved protocols for sterilization and verification of ice drilling equipment.

KAUST RepositoryThe growth rates of planktonic microbes in the pelagic zone of the Eastern Mediterranean Sea 28 are nutrient limited, but the type of limitation is still uncertain. During this study, we 29 investigated the occurrence of N and P limitation among different groups of the prokaryotic 30 and eukaryotic (pico-, nano-, and micro-) plankton using a microcosm experiment during 31 stratified water column conditions in the Cretan Sea (Eastern Mediterranean). Microcosms 32 were enriched with N and P (either solely or simultaneously) and the PO 4 turnover time, 33 prokaryotic heterotrophic activity, primary production and the abundance of the different 34 microbial components were measured. Flow cytometric and molecular fingerprint analyses 35showed that different heterotrophic prokaryotic groups were limited by different nutrients; 36 total heterotrophic prokaryotic growth was limited by P, but only when both N and P were 37 added, changes in community structure and cell size were detected. Phytoplankton were N 38 and P co-limited, with autotrophic pico eukaryotes being the exception as they increased even 39 when only P was added after a 2-day time lag. The populations of Synechococcus and 40Prochlorococcus were highly competitive with each other; Prochlorococcus abundance 41 increased during the first two days of P addition but kept increasing only when both N and P 42 were added, whereas Synechococcus exhibited higher pigment content and increased in 43 abundance three days after simultaneous N and P additions. Dinoflagellates also showed 44 opportunistic behavior at simultaneous N and P additions, in contrast to diatoms and 45 coccolithophores, which diminished in all incubations. High DNA content viruses, selective 46 grazing and the exhaustion of N sources probably controlled the populations of diatoms and 47 coccolithophores. 48