Thesis (M.Sc.)--Chulalongkorn University, 2007

The isolation of lipase-producing bacteria were isolated from sources of 12 soil samples and 10 composts in Thailand, using enrichment media containing olive oil. The primary screening was carried out employing tributyrin agar plate and Rhodamine B supplemented with olive oil was used for secondary lipase screening. Fifty-five lipase-producing isolates were determined lipase activity by using p-nitrophenyl palmitate as substrate. The results showed that Stenotrophomonas maltophilia CU22 exhibited the highest specific activity. Also, lipase from S. maltophilia was catalyzed transesterification of the palm oil and methanol in non-solvent media and showed 7% methyl ester conversion. To improve lipase activity, random mutagensis by UV irradiation was used. At 10 sec expose time, the death rate with 96.67%, 47 mutants was as subject to test hydrolytic assay. Ten mutants with higher lipase specific activity were subcultured twenty times and then investigated transesterification. UV107, UV1016 and UV 1048 showed %conversion higher than wild type, were 7.56, 9.30 and 7.3 %. DNA and amino acid sequencing of partial lipase gene of wild type and UV1016 , were compared. The result showed nucleotide substitution at 1765, 1766 and 1768 with different amino acid substitution, were obtained. There are Asn568->Asp, Gln589->Trp and Arg590->Gly.