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High throughput V3-16S rRNA amplicon sequencing data was used for evaluating differences between free-living (FL, <1.2-0.2 μm) and particle-associated (PA, >1.2 μm) bacterial communities, and their spatial variation between inner fjord (IF) and outer fjord (OF) of Kongsfjorden. A total of 4,454,142 high quality sequences obtained clustered into 32,058 OTUs. A majority of these sequences were affiliated with Proteobacteria (59.8%), followed by Bacteroidetes (29.02%), Firmicutes (5.9%), Actinobacteria (2.84%), Cyanobacteria (1.04%), and others (1.4%). The highest bacterial diversity was recorded in the inner fjord free-living (IF_FL) fraction whilst the lowest was observed in the outer fjord free-living (OF_FL) fraction. There was a clear spatial variation among FL bacterial communities, while PA communities remained similar at both sampling locations. The free-living bacterial community differs from particle-associated community and had relatively higher abundance (>4-fold) of Alteromonas and Pseudoalteromonas, while PA community was relatively more enriched with Balneatrix, Ulvibacter, Formosa, Candidatus Planktomarina, Sulfitobacter, Loktanella, members of SAR116, and Acidimicrobiales. In addition, two major bacterial taxa, Polaribacter and SAR11, co-occurred in both FL and PA fractions with varied proportions in IF and OF. These results suggest co-occurrence of PA specialist as well as generalist bacterial groups in Kongsfjorden. Further, high bacterial diversity in the IF_FL fraction indicates possible role of glacial inputs in modulating diversity of free-living bacterial community in Kongsfjorden.

Microbiological studies of polar ice at different depths may provide important comparisons, as they preserve records of microbial cells and past climate. In this study, we examined bacterial abundance, diversity and glaciochemical composition from three depths of an ice core from coastal Dronning Maud Land, East Antarctica. Higher bacterial abundance corresponded with high in situ sea-salt Na(+) and dust concentration, suggesting that bacteria might have been transported and deposited into ice along with dust particles and marine aerosols. Fourteen bacterial isolates belonging to the genera Methylobacterium, Brevundimonas, Paenibacillus, Bacillus and Micrococcus were retrieved. Frequent isolation of similar bacterial genera from different cold environments suggests that they possess features that enable survival and metabolism for extended periods of time at sub-zero temperatures. The highest number and diversity of recoverable bacteria was obtained from 49 m depth corresponding to 1926 AD and consisted of bacteria from 4 different genera whereas at 11 m (1989 AD) and 33 m (1953 AD) samples only species belonging to the genera Bacillus was recovered. Among the Bacillus species, Bacillus aryabhattai which has been reported only from the upper stratosphere, was isolated and is the first record from the Earth's surface. Methylobacterium was the most dominant genera at 49 m depth and its prevalence is attributable to a combination of high in situ methanesulfonate concentration, specialized metabolism and environmental hardiness of Methylobacterium. Some of the isolated bacteria were found to respire and grow using methanesulfonate, suggesting that they may utilize this substrate to sustain growth in ice. In addition, NO(3)(-) (2.93-3.69 μM), NH(4)(+) (1.45-3.90 μM) and PO(4)(3-) (0.01-0.75 μM) present in the ice could be potential sources fueling bacterial metabolism in this environment. It could be deduced from the study that variation in bacterial abundance and diversity was probably associated with the prevailing in situ conditions in ice.

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