Characterization of polyglutamic acid produced from thermotolerant bacterial isolates
Poonsuk Prasertsan, Assoc. Prof., D. of Industrial Biotech., F. of Agro-Industry, PSU.
Siriporn Madla, M.Sc. Student in Biotech., PSU.
Pawadee Methakanon, National Metal and Materials Tech. Center, National Sci. and
Tech. Development Agency, Bangkok
Corresponding e-mail : ppoonsuk@ratree.psu.ac.th
Grant : Graduate School, PSU.
Presented : International Symposium on the Bioconversion of Renewable Raw Materials,
25-29 September 2000, Hannover and Braunschweig, Germany
Key words : biopolymer, polyglutamic acid, characterization, thermotolerant, bacteria
Forty-two strains of polymer-producing bacteria were isolated from wastewater taken from six seafood processing plants and the Hat Yai Municipal wastewater treatment plant as well as sample from a hot spring (54oC). Comparison on the polymer yields from these strains were carried out by cultivating in the polyglutamic medium at 45oC for 48 h on a shaker at 200 rpm. Ten strains were selected due to their high polymer yields (>50 g/l). They were found to be thermotolerant strains
since they could grow and produce polymer both at 30oC and 45oC. Three of them were chosen for further studies due to their similar maximum polymer yields (54.45-58.08 g/l). Polymers produced from the selected isolates, strain no. FT 1.2, KF 4.1 and WD 90, were purified and found to contain alpha-amino acids, without any aromatic amino acid, and sugar with the total sugar values of 13.27%, 12.99% and 9.48%, respectively. The polymers were soluble in water and insoluble in any twelve organic solvents tested. Besides, they also possessed the flocculating property. Their flocculating activities (0.075-0.205) using kaolin suspension and the flocculating rates (6.53-16.06%) were much lower than those from using the crude polymers (the values were 4.625-9.506, and 74.62-94.29%, respectively). Molecular weights of the polymers from the isolates FT 1.2, KF 4.1 and WD 90 were found to be 54,192, 59,567 and 58,839 Daltons, with the polydispersity values of 3.109, 3.303 and 2.771, respectively.
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