Optimization of Cultural Conditions for Production of Extracellular Polymeric Substances (EPS) by Serpentine Rhizobacterium Cupriavidus pauculus KPS 201

Extracellular polymeric substances (EPS) are complex biopolymers produced by a wide array of microorganisms for protection against dessication, aggregation, adhesion, and expression of virulence. Growth associated production of EPS by Ni-resistant Cupriavidus pauculus KPS 201 was determined in batch culture using sodium gluconate as the sole carbon source. The optimum pH and temperature for EPS production were 6.5 and 25°C, respectively. Optimal EPS yield (118？μg/mL) was attained at 0.35% Na-gluconate after 72？h of growth. Cupriavidus KPS 201 cells also utilized glutamate, acetate, pyruvate, fumarate, malate, malonate, formate, citrate, and succinate for EPS production. Although EPS production was positively influenced by the increase of nitrogen and phosphate in the growth medium, it was negatively influenced by nickel ions. Compositional analysis of the purified EPS showed that it is a homopolymer of rhamnose containing uronic acid, protein, and nucleic acid. Presence of lipids was also detected with spectroscopy. Non-destructive EPS mediated biofilm formation of KPS 201 was also visualized by epifluorescence microscopy. 1. Introduction Extracellular polymeric substances (EPS) are biosynthetic polymers of microbial origin produced in natural as well as artificial environments by single species or in heterogeneous communities. Irrespective of their origin, EPS are localized at or outside the bacterial cell surface and composed of a variety of high molecular weight organic macromolecules such as polysaccharides, proteins, nucleic acids, and phospholipids [1]. These exopolymers result from microbial processes like active secretion, shedding of cell surface materials, cell lysis, and adsorption from the environment. Based on their physical state, EPS can be distinguished as bound and soluble forms. The bound EPS include microbial sheaths, capsular polymers, condensed gel, and so forth while the soluble EPS include soluble macromolecules, colloids and slimes. According to the metabolism of bacterial cells, the soluble EPS are considered to be actively secreted by bacteria and are biodegradable, while the bound ones remain attached to active and inert biomass or are molecules resulting from cell lysis. The production of EPS by bacteria in culture depends on phases of growth, nutritional status, and the environmental conditions. The production of water-soluble EPS by Rhodopseudomonas acidophila was influenced by the C？:？N ratio and polymer production was found to be dependent on the nature of carbon sources used [2]. Similarly, in anaerobically growing