Bacterial abundance and composition in marine sediments beneath the Ross Ice Shelf, Antarctica

Abstract

Marine sediments of the Ross Sea, Antarctica, harbor microbial communities that play a significant role in the decomposition, mineralization, and recycling of organic carbon (OC). In this study, the cell densities within a 153-cm sediment core from the Ross Sea were estimated based on microbial phospholipid fatty acid (PLFA) concentrations and acridine orange direct cell counts. The resulting densities were as high as 1.7 × 10⁷ cells mL⁻¹ in the top ten centimeters of sediments. These densities are lower than those calculated for most near-shore sites but consistent with deep-sea locations with comparable sedimentation rates. The δ¹³C measurements of PLFAs and sedimentary and dissolved carbon sources, in combination with ribosomal RNA (SSU rRNA) gene pyrosequencing, were used to infer microbial metabolic pathways. The δ¹³C values of dissolved inorganic carbon (DIC) in porewaters ranged downcore from -2.5‰ to -3.7‰, while δ¹³C values for the corresponding sedimentary particulate OC (POC) varied from -26.2‰ to -23.1‰. The δ¹³C values of PLFAs ranged between -29‰ and -35‰ throughout the sediment core, consistent with a microbial community dominated by heterotrophs. The SSU rRNA gene pyrosequencing revealed that members of this microbial community were dominated by β-, δ-, and γ-Proteobacteria, Actinobacteria, Chloroflexi and Bacteroidetes. Among the sequenced organisms, many appear to be related to known heterotrophs that utilize OC sources such as amino acids, oligosaccharides, and lactose, consistent with our interpretation from δ¹³CPLFA analysis. Integrating phospholipids analyses with porewater chemistry, δ¹³CDIC and δ¹³CPOC values and SSU rRNA gene sequences provides a more comprehensive understanding of microbial communities and carbon cycling in marine sediments, including those of this unique ice shelf environment.

Indications for algae-degrading benthic microbial communities in deep-sea sediments along the Antarctic Polar Front

“…These clades seemed to be also dominant in the surface sediments along the Antarctic Polar Front. Gammaproteobacteria might be particularly important in Arctic (Bienhold et al, 2011;Ravenschlag et al, 1999) and Antarctic sediments (Carr et al, 2013;Jamieson et al, 2013), which is also indicated by our study. However, the data on key clades in deep-sea sediments is becoming sparser with increasing phylogenetic resolution.…”

“…The standing stocks of benthic meioand macrofaunal assemblages of the Southern Ocean further suggest a relatively high supply of POC to the sediments (Brandt et al, 2007). Interestingly, in the Southern Ocean, benthic communities of regions with high surface water productivity were found to be similar to those in low productivity regions (Jamieson et al, 2013) and in sediments below the Ross ice-shelf (Carr et al, 2013), indicating that other factors than just the extent of primary productivity play a role. However, as research focused on macrofaunal benthic communities, little is known about microbial communities in sediments along the Antarctic Polar Front.…”

Evolutionary Dynamics of the Prokaryotic Adaptive Immunity System CRISPR-Cas in an Explicit Ecological Context

“…More specifically, in deep-sea marine hydrothermal sediments, the cell densities of hyperthermophilic prokaryotes (primarily, Archaea) appear to vary approximately from 10 5 to 10 8 cells per g (72,(75)(76)(77)(78)(79). In contrast, substantially higher prokaryotic cell densities, on the order of 10 9 cells per g and even greater have been reported for shallow water, mesophilic sediments (80)(81)(82)(83)(84)(85)(86).…”

Vertical distribution of Fe and Fe(III)-reducing bacteria in the sediments of Lake Donghu, China

“…may be the higher levels of carbon in sediments. Previous studies of microbial abundance in sediments indicated that those with larger amounts of carbon generally had a larger microbial population (Carr et al 2013;Hardison et al 2013;Dong et al 2014). The overall microbial abundance in sediments ultimately depends on the availability of suitable nutrients and energy sources (Carr et al 2013).…”