Structural characterization and ecological roles of a novel exopolysaccharide from the deep-sea psychrotolerant bacterium Pseudoalteromonas sp. SM9913

Abstract

Pseudoalteromonas sp. SM9913 is a psychrotolerant bacterium isolated from deep-sea sediment. The structural characterization and ecological roles of the exopolysaccharide (EPS) secreted by this strain were studied in this work. The yield of the EPS increased as the culture temperature decreased in the range 30-10 6C, and it reached 5.25 g l "1 (dry weight) under optimal growth conditions (15 6C, 52 h). EPS fraction was purified and its structure was identified by the combination of NMR spectra, high-resolution mass spectrometry (HRMS) analysis and methylation analysis. The ratio of the sugar units, the acetyl group and the ethoxyl group was close to 4 : 5 : 1. The major sugar unit of the EPS was 6-linked glucose (61.8 %); other sugar units present included terminal arabinofuranosyl (11.0 %) and glucopyranosyl (11.2 %) residues and a small amount of other sugar derivatives. Its structure was different from EPSs reported for other marine bacteria.Besides the structural elucidation of the EPS, its ecological roles were studied. This EPS could enhance the stability of the cold-adapted protease MCP-01 secreted by the same strain through preventing its autolysis. It could bind many metal ions, including Fe 2+ , Zn 2+ , Cu 2+ , Co 2+ . It was also a very good flocculating agent and could conglomerate colloidal and suspended particles. These results indicated that the EPS secreted by strain SM9913 might help this strain enrich the proteinaceous particles and the trace metals in the deep-sea environment, stabilize the secreted cold-adapted proteases and avoid its diffusion. This is believed to be the first report on the structure of the EPS secreted by a deep-sea psychrotolerant bacterium and its ecological roles. According to these results and other studies, a schematic diagram of the lifestyle of the deep-sea psychrotolerant strain SM9913 is suggested.

Comparative genomics reveals a deep-sea sediment-adapted life style of Pseudoalteromonas sp. SM9913

“…SM9913 Q-L Qin et al showed that SM9913 can produce large amounts of highly acetylated EPS (Qin et al, 2007a). These EPS can protect the cold-adapted protease MCP-01 produced by SM9913 from autolysis and can bind many metal ions because of their net negative charge and acidic properties (Qin et al, 2007a).…”

“…SM9913 Q-L Qin et al showed that SM9913 can produce large amounts of highly acetylated EPS (Qin et al, 2007a). These EPS can protect the cold-adapted protease MCP-01 produced by SM9913 from autolysis and can bind many metal ions because of their net negative charge and acidic properties (Qin et al, 2007a). Some deepsea bacteria with sequenced genomes, such as Idiomarina loihiensis (Hou et al, 2004) and A. macleodii 'deep ecotype' (Ivars-Martinez et al, 2008), have EPS biosynthesis genes, showing that the production of EPS may be a common strategy that deep-sea bacteria adopt to endure extreme conditions.…”

“…Some deepsea bacteria with sequenced genomes, such as Idiomarina loihiensis (Hou et al, 2004) and A. macleodii 'deep ecotype' (Ivars-Martinez et al, 2008), have EPS biosynthesis genes, showing that the production of EPS may be a common strategy that deep-sea bacteria adopt to endure extreme conditions. EPS can endow bacteria with other advantages as well, such as the ability to adhere to and colonize surfaces, and can speed biochemical interactions, protect the cell and concentrate dissolved organic matter in the marine environment (Nichols et al, 2005;Qin et al, 2007a).…”

“…Other genes of the siderophore uptake system, such as TonB2 and the TonB system transport proteins, ExbB2 and ExbD2 (Ghysels et al, 2005), are all present in SM9913. Iron is always a growth-limiting factor for marine bacteria (Qin et al, 2007a). Thus, it is reasonable to assume that the siderophore uptake system helps SM9913 adsorb iron in the marine environment.…”

“…Pseudoalteromonas sp. SM9913, isolated from deep-sea sediment at a water depth of 1855 meters near the Okinawa Trough, is a psychrophilic strain that produces a large quantity of proteases and exopolysaccharides (EPSs), indicating its function in the degradation of sedimentary particulate organic nitrogen and its potential uses in biotechnology applications (Chen et al, 2003;Qin et al, 2007a). Aside from its adaptability to cold temperatures, the deep-sea-specific features of SM9913 remain largely unknown.…”