Factors influencing the production of extracellular polymeric substances by Rhodopseudomonas acidophila

The effects of cell growth phase, substrate type, NaCl, CaCl2 and C/N ratio on the anaerobic production of water-soluble extracellular polymeric substances (EPS) by the photosynthetic bacterium, Rhodopseudomonas acidophila, were examined. The protein content of the EPS decreased from 96.7 to 39.0 mg g−1 dry cell weight with increase in cultivation time from 20 to 100 h, but remained almost unchanged thereafter. EPS production was inversely proportional to bacterial dry weight. The amount of EPS produced by R. acidophila decreased in order of the following carbon sources: benzoate>acetate>butyrate>propionate>succinate>malonate. High NaCl concentrations resulted in more EPS, but CaCl2 concentration had little or no influence on the EPS production. The magnitude of carbon and nitrogen sources influenced the total amount of EPS, and also the ratio of carbohydrate to protein in its composition.