Characterization of Extracellular Polysaccharides (EPS) Produced by Thermal Bacillus and Determination of Environmental Conditions Affecting Exopolysaccharide Production

In this study, the neutral monosaccharide composition of the Extracellular Polysaccharide (EPS), extracted from thermal Bacillus, was determined by Liquid Chromatography-Mass Spectrometry and High Performance Liquid Chromatography. Our analysis indicated that the EPS consisted of rhamnose, mannose, galactose, glucose, fructose, arabinose and xylose. In addition to the neutral sugars in the EPS, it also contained 230 mg protein/g EPS and 17.18 mg uronic acid /g EPS. The X-ray diffraction data indicated mainly of amorphous nature (80 %) and the presence of chitin, chitosan, protein and calcite. Thermogravimetric analysis curve showed that degradation of EPS takes place in three steps (13.38% at < 180 °C. 45.62% at 180-500 °C, 25.55% at > 500 oC) indicating moisture content and high content of carboxyl group, pyrolysis temperature and decomposition of calcite crystals, respectively. Additionally, laboratory batch experiments were performed characterize the effects of different natural organic acids, pH levels, temperatures and Cr(VI) concentrations on microbial EPS production by Bacillus licheniformis B22. Our results indicate that organic acids caused enhanced EPS release. Alginic acid was the most efficient organic acid at EPS production in B. licheniformis B22. The optimum pH level was 6.0-7.0 and the highest EPS production was observed at 50 ºC for B. licheniformis B22. In addition, EPS production increased with increased chromium in the growth medium due to the toxic effect of Cr(VI) on cells. Maximum EPS production was observed when 150 mg/L Cr(VI) was added to the medium.