Screening of glutaminase in Llactobacillus spp.

초록

Lactobacillus spp. are known as GRAS(generally regard as safe) bacteria widely used in food industry. In this study we screened over 100 lactobacilli isolates for their glutaminase activity. Glutaminase (glutamine amidotransferase) deaminates glutamine converting it to glutamic acid, sodium salt of which is well known as a flavor substance. For enzyme assay we measured the NADH produced during the conversion of L-glutamine to 2-oxaloglutarate spectrophotometrically. Among 105 lactobacilli isolates screened, 10 isolates showed no glutaminase activity. One isolate showing the highest activity was selected and identified as Lactobacillus plantarum by 16S rDNA sequence comparison. The strain L. plantarum KLB 213 showed glutminase activity of 0.748 unit/mg protein. In order to clone the glutaminase gene from KLB 213 we employed degenerate-PCR to obtain 431bp internal gene fragment. Lack of glutaminase activity of the 10 isolates appeared to be due to their lack of corresponding gene. Sequence comparison of the 431 bp internal fragment revealed 99% identity to the reported glutaminase sequence of L. plantarum genome. Presently, full gene cloning is under way by using single-primer PCR.