Effects of Incubation Temperature on Growth and Production of Exopolysaccharides by an Antarctic Sea Ice Bacterium Grown in Batch Culture

Abstract

The sea ice microbial community plays a key role in the productivity of the Southern Ocean. Exopolysaccharide (EPS) is a major component of the exopolymer secreted by many marine bacteria to enhance survival and is abundant in sea ice brine channels, but little is known about its function there. This study investigated the effects of temperature on EPS production in batch culture by CAM025, a marine bacterium isolated from sea ice sampled from the Southern Ocean. Previous studies have shown that CAM025 is a member of the genus Pseudoalteromonas and therefore belongs to a group found to be abundant in sea ice by culture-dependent and -independent techniques. Batch cultures were grown at ؊2°C, 10°C, and 20°C, and cell number, optical density, pH, glucose concentration, and viscosity were monitored. The yield of EPS at ؊2°C and 10°C was 30 times higher than at 20°C, which is the optimum growth temperature for many psychrotolerant strains. EPS may have a cryoprotective role in brine channels of sea ice, where extremes of high salinity and low temperature impose pressures on microbial growth and survival. The EPS produced at ؊2°C and 10°C had a higher uronic acid content than that produced at 20°C. The availability of iron as a trace metal is of critical importance in the Southern Ocean, where it is known to limit primary production. EPS from strain CAM025 is polyanionic and may bind dissolved cations such at trace metals, and therefore the presence of bacterial EPS in the Antarctic marine environment may have important ecological implications.Sea ice is a major component of polar regions, covers millions of square kilometers even at the end of the polar summer (21), and provides a home to unique communities dominated by microorganisms (35). Sea ice begins to form as the temperature of seawater, with a salinity of 3.5%, drops to Ϫ1.8°C. As ice develops, a salting-out process occurs in which the marine salts excluded from the ice are concentrated in brine pockets. Brine channels develop as the ice rises above sea level. The dense brine drains through the layer of columnar congelation ice by gravity and flows to the underlying seawater (7). The sea ice produces highly variable microenvironments in terms of temperature, salinity, nutrient concentration, and light intensities within the columns, which may be as thick as 2 m. Salinity in sea ice brine can range from near that of freshwater to Ͼ15% at the ice-seawater interface (35). Temperatures can range from 0°C to Ϫ35°C. Sea ice is thus one of the coldest habitats on earth for marine life (22).In spite of these extremes, up to 20 to 30% of primary production in sea ice cycles through heterotrophic bacteria (24, 30). Complex microbial communities, dominated by diatoms in close association with bacteria (30), are concentrated in the lower 10 to 20 cm of sea ice, where nutrients are available from the seawater and light is available from the surface (35). Abundant bacterial populations have been found in thick annual pack ice, with psychrophilic bacteria being particularl...

Metagenomic Analysis of Stress Genes in Microbial Mat Communities from Antarctica and the High Arctic

“…Many studies have shown the important role of EPS in buffering and cryoprotection for diverse microorganisms against ice crystal damage and high salinity (25,34,35). Cyanobacteria produce large amounts of EPS (24,36) and were the primary source of EPS genes in the mats from both Antarctica and the Arctic.…”

“…Sulfate-reducing bacteria in the Deltaproteobacteria may also produce large amounts of EPS (5, 57). Nichols et al (34) showed that Proteobacteria (especially Gammaproteobacteria) and Bacteroidetes, which were common phyla in all three polar metagenomes, are able to synthesize EPS in response to low temperatures, implying that this is a cold-adaptation process.…”

“…Cyanobacteria produce large amounts of EPS (24,36) and were the primary source of EPS genes in the mats from both Antarctica and the Arctic. EPS allow bacterial aggregate formation, which in turn provides opportunities for close biogeochemical interactions (34). In the cryophilic gammaproteobacterium Psychromonas ingrahamii, production of EPS may sequester water from the ambient saltwater, lowering the freezing point (44).…”

Key role of organic complexation of iron in sustaining phytoplankton blooms in the Pine Island and Amundsen Polynyas (Southern Ocean)

“…The regenerated Fe can be immediately utilized by plankton or become trapped along with organic matter when sea-ice forms later in the season (Kepkay, 1994;Thomas et al, 2001;Lannuzel et al, 2007Lannuzel et al, ,2008Ackermann et al, 1994;Reimnitz et al, 1993;Sherwood, 2000;Smedsrud, 1998). This material, together with organic matter produced by the microbial community living within the sea-ice, are released the following season when the sea-ice melts (Lannuzel et al, 2010) and act as a source of dissolved ligands (Aguilar-Islas et al, 2008;Calace et al, 2001;Nichols et al, 2005;Pankowski and McMinn, 2008). Iron released from melting sea-ice may be pivotal for initiating the spring phytoplankton bloom, thanks to the presence of ligands that solubilize Fe.…”

Genome Sequence of Lentisphaera araneosa HTCC2155 T , the Type Species of the Order Lentisphaerales in the Phylum Lentisphaerae

“…The genome contains several putative genes connected with EPS production-22 predicted glycosyltransferases, several of which are located two genes downstream from putative UDP-N-acetylglucosamine 2-epimerases (epsC homologs) in eps gene cluster-like configurations (12,14). EPS production has been connected to psychrotolerance in several strains (1,6,8) and with increased pressure (6). The highest relative abundances of L. araneosa were measured in upper mesopelagic waters off the Oregon coast and at the Bermuda Atlantic Time Series station (2).…”