High Prevalence of Gammaproteobacteria in the Sediments of Admiralty Bay and North Bransfield Basin, Northwestern Antarctic Peninsula

Abstract

Microorganisms dominate most Antarctic marine ecosystems, in terms of biomass and taxonomic diversity, and play crucial role in ecosystem functioning due to their high metabolic plasticity. Admiralty Bay is the largest bay on King George Island (South Shetland Islands, Antarctic Peninsula) and a combination of hydro-oceanographic characteristics (bathymetry, sea ice and glacier melting, seasonal entrance of water masses, turbidity, vertical fluxes) create conditions favoring organic carbon deposition on the seafloor and microbial activities. We sampled surface sediments from 15 sites across Admiralty Bay (100-502 m total depth) and the adjacent North Bransfield Basin (693-1147 m), and used the amplicon 454-sequencing of 16S rRNA gene tags to compare the bacterial composition, diversity, and microbial community structure across environmental parameters (sediment grain size, pigments and organic nutrients) between the two areas. Marine sediments had a high abundance of heterotrophic Gammaproteobacteria (92.4% and 83.8% inside and outside the bay, respectively), followed by Alphaproteobacteria (2.5 and 5.5%), Firmicutes (1.5 and 1.6%), Bacteroidetes (1.1 and 1.7%), Deltaproteobacteria (0.8 and 2.5%) and Actinobacteria (0.7 and 1.3%). Differences in alpha-diversity and bacterial community structure were found between the two areas, reflecting the physical and chemical differences in the sediments, and the organic matter input.

Keywords: Antarctica; bacterial community structure; marine sediments; microbial diversity; polar microbiology.

FIGURE 1

Sampling map with 15 selected stations, 1–9 inside Admiralty Bay and 10–15 in the North Bransfield Basin, Northwestern Antarctic Peninsula.

FIGURE 2

Taxonomic composition and relative abundance of 16S rRNA sequences based on bacterial phyla and proteobacterial classes. Samples 1–9 belong to Admiralty Bay, and 10–15 are from North Bransfield Basin.

FIGURE 3

Shared OTUs between the samples. The numbers on the x and y axes correspond to the sample numbers (1–15). The smaller the circles, the less OTUs are shared, and the bigger the circles, the more OTUs are shared.

FIGURE 4

Non-metric multidimensional scaling (nMDS) ordination. Black dots represent stations 1–9 (Admiralty Bay), and white dots are stations 10–15 (North Bransfield Basin). Each arrow is significantly correlated to the ordination (envfit, p < 0.05), and represents the direction and strength of the environmental gradient (Clay, Silt, Sand, Phaeo, Phaeopigments; Chl, Chlorophyll; CPE, Chloroplast Pigment Equivalent, Carbonate; OM, Organic Matter; TOC, Total Organic Carbon; Total N, Total Nitrogen; C/N, Carbon to Nitrogen ratio).