Screening of thermotolerant polymer-producing bacteria and characterization of the polymers

Siribhorn Madla, M.Sc. Student in Biotech., PSU.
Poonsuk Prasertsan, Assoc. Prof., D. of Industrial Biotech., F. of Agro-Industry, 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 : The 12th Annual Meeting of the Thai Society for Biotechnology "Biotechnology : Impacts&Trends", 1-3 November 2000, Kanchanaburi, Thailand
Key words : screening, thermotolerant, polymer, characterization, bacteria

Various media for growth of bacteria producing polyglutamic acid (PGA), glycoprotein (GP), polysaccharide (PS), protein (PR), glycolipid (GL), and polylysine (PL), were used for isolation. Fifty-four strains of polymer-producing bacteria were achieved from PGA (42 strains), GP (1 strain), PS (4 strains), PR (3 strains), GL (4 strains), and none produced PL. The isolates were cultivated in the medium at 45oC for 48 h using rotary shaker (200 rpm). Ten strains of PGA-producing bacteria were selected due to their high polymer yields (>50 g/l). They were found to be thermotolerant strains since they could grow and give high PGA yield both at 30oC as well as at 45oC. Three of the strains, WD 90, KF 4.1 and FT 1.2, were selected for further studies. Polymers produced from these strains were purified and analysed for their composition. Results indicated that purified polymers from WD 90, KF 4.1 and FT 1.2, contained alpha-amino acids without any aromatic amino acid, the total sugar contents were 9.5%, 12.9% and 13.3% respectively. The polymers were soluble in water but insolu-ble in twelve organic solvents tested. Besides, they also possessed the flocculating properties. Their flocculating activities using kaolin suspension (~0.1-0.2) and the flocculating rates (6.5-16.1%), were much lower than those observed with crude polymers (4.6-9.5 and 74.6-94.3%, respectively). Molecular weights of the polymers from the isolates WD 90, KF 4.1 and FT 1.2 were found to be 58,839, 59,567 and 54,192 Daltons, with polydispersity values of 2.8, 3.3 and 3.1, respectively.
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