Exopolysaccharide production by Antarctic marine bacteria

Antarctic marine bacteria isolated from sea ice and Southern Ocean particulate material were screened for exopolysaccharide (EPS) production. Ten strains were characterized using phenotypic (morphology), chemotaxonomic (whole cell fatty acid profiles) and phylogenetic (16S rDNA sequencing) techniques. These isolates were representatives of four genera including Pseudoalteromonas, Shewanella, Polaribacter and Flavobacterium, with one strain constituting a new bacterial genus in the family Flavobacteriaceae. After further phenotypic characterisation, this strain was given the name Olleya marilimosa, gen. nov., sp. nov. The ten strains were grown in batch culture and the EPS extracted, purified and partially characterized. Crude chemical, monosaccharide and molecular weight determinations showed that the EPS were diverse, even among closely related isolates. All EPS contained uronic acids to varying degrees and some also contained sulfate groups. Two EPS showed the presence of acetyl groups, with pyruvate present in at least one polysaccharide. The bacteria belong to phylogenetic groups that are dominant in sea ice and Southern Ocean particulate material according to previous studies that used culture dependent and independent techniques. These isolates were psychrotolerant, grew between 2 to 25°C and had growth optima at approximately 20°C. Growth and EPS production of one isolate belonging to the genus Pseudoalteromonas was examined at three temperatures: -2°C, 10°C and 20°C. EPS yield at -2°C and 10°C was thirty-fold higher than at 20°C. The EPS showed higher levels of uronic acids at lower temperature. The metal binding ability of a high molecular weight, highly viscous EPS produced by one sea ice bacterium was examined. High affinities for cadmium and copper were observed at the low concentration of EPS used. These results are a first step in assessing the ability of EPS produced by Antarctic marine bacteria to chelate dissolved trace metal such as iron, which are essential for growth and are limiting primary production in the Southern Ocean. The examination of EPS production by Antarctic marine bacteria provides new evidence that these biopolymers are abundant and diverse. Partial structural elucidation reveals important structure-function relationships. EPS such as those examined in this study may have a cryoprotective role or may impact on the availability of important trace metals. These findings point to the wider ecological role of EPS within the Antarctic marine environment. This study also provides incentive for further investigation into commercial usefulness of these biopolymers.