Previous study showed that some Gram-negative bacteria possess human blood group activity. Among them, Escherichia coli O86 has high blood group B activity and weak blood group A activity. This is due to the cell surface O-antigen structure, which resembles that of human blood group B antigen. In this study, we sequenced the entire E. coli O86 antigen gene cluster and identified all the genes responsible for O-antigen biosynthesis by sequence comparative analysis. The blood group B-like antigen in E. coli O86 O-polysaccharide was synthesized by sequentially employing three glycosyltransferases identified in the gene cluster. More importantly, we identified a new bacterial glycosyltransferase (WbnI) equivalent to human blood group transferase B (GTB). The enzyme substrate specificity and stepwise enzymatic synthesis of blood group B-like antigen revealed that the biosynthetic pathway of B antigen is essentially the same in E. coli O86 as in humans. This new finding provides a model to study the specificity and structure relationship of blood group transferases and supports the hypothesis of anti-blood group antibody production by bacterial stimulation.

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.

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