Yield and physicochemical properties of EPS from Halomonas sp. strain TG39 identifies a role for protein and anionic residues (sulfate and phosphate) in emulsification of n-hexadecane

In this study, we investigated the yield and physicochemical properties of the high molecular weight extracellular polymeric substance (HMW-EPS) produced by Halomonas sp. strain TG39 when grown on different types and ratios of substrates. Glucose (1% w/v) and a peptone/yeast extract ratio of 5.1 (0.6% w/v final concentration) yielded an EPS fraction (HMW-glucose) exhibiting the highest anionic activity (20.5) and specific emulsifying activity (EI 24 = 100%) compared to EPS produced by cells grown on mannitol, sucrose, malt extract or no carbon source. The HMW-EPS fractions were capable of binding ≈255-464 mg of methylene blue (MB) per gram of EPS, which represents the highest reported binding of MB by a bacterial EPS. A comparative evaluation of these properties to those of commercial hydrocolloids indicated that the combined effect of protein and anionic residues of the HMW-EPS contributed to its ability to emulsify n-hexadecane. Liquid chromatography revealed the HMW-glucose EPS to be a heterogeneous polymer with a polydispersity index of 1.8. This work presents evidence of a correlation between the anionic nature and protein content of bacterial EPS with its emulsifying qualities, and identifies EPS produced by strain TG39 as a high MB-binding bacterial sorbant with potential biotechnological application. © 2008 Wiley Periodicals, Inc.