Sand aggregation by exopolysaccharide-producing Microbacterium arborescens--AGSB

In the rhizosphere, exopolymers are also known to be useful to improve the moisture-holding capacity. The ability of the isolates from coastal sand dunes to produce exopolymers was determined. Among which the isolate, showing very high production of exopolysaccharide (EPS), Microbacterium arborescens--AGSB, a facultative alkalophile was further studied for exopolymer production. The isolate a gram-positive non-spore forming, slender rod, catalase positive, oxidase negative, showed growth in 12% sodium chloride. The culture was found to produce exopolymer which showed good aggregation of sand which has an important role in the stabilization of sand dunes. The exopolymer was further analysed. The cold isopropanol precipitation of dialysed supernatants grown in polypeptone yeast extract glucose broth produced partially soluble EPSs with glucose as the sole carbon source. Chemical analysis of the EPS revealed the presence of rhamnose, fucose, arabinose, mannose, galactose and glucose. On optimization of growth parameters (sucrose as carbon source and glycine as nitrogen source), the polymer was found to be a heteropolysaccharide containing mannose as the major component. It was interesting to note that the chemical composition of the exopolymers produced from both unoptimized and optimized culture conditions of Microbacterium arborescens--AGSB is different from those of other species from the same genera. This study shows that marine coastal environments such as coastal sand dunes, are a previously unexplored habitat for EPS-producing bacteria, and that these molecules might be involved in ecological roles protecting the cells against dessication especially in nutrient-limited environments such as the coastal sand dunes more so in the extreme conditions of pH. Such polysaccharides may help the bacteria to adhere to solid substrates and survive during the nutrient limitations.