Isolation and Identification of a Strain Lactococcus lactis ssp. with Glutathione Biosynthetic Capability

Abstract:

A bacterial strain that produces glutathione(GSH) was screened from vegetable garden soil based on a polymerase chain reaction (PCR) protocol which could rapidly and specifically identify the gshB gene coding for GSH synthetase. Phylogenetic analysis based on 16S rDNA revealed that this strain belongs to L. lactis ssp. cremoris. Scanning electron microscope analysis indiczated that its morphology characteristics were most consistent with Lactococcus lactis. So we suggested that the strain belonged to L. lactis ssp. cremoris and named L. lactis CCSYU10100. The intracellular level of GSH in stationary-phase cells of strain CCSYU10100 grown aerobically in chemically-defined medium was 2.39±0.21 nmol/mg protein. Other than GSH, cysteinylglycine was identified by HPLC. The partial gshB gene sequence and the deduced amino acid sequence of strain CCSYU10100 were highly similar with that of Pseudomonas among different microorganisms, which indicated that strain CCSYU10100 probably possesses independent gshB gene. Noticeably, the GC content of the partial gshB gene of strain CCSYU10100 was 61.55%, and the GC content of whole genome of L. lactis is 35%-40%, which seggusted that the gshB gene might not be an inherent part of strain CCSYU10100.Considering Pseudomonas fluorescens exists in the soil widely, it was speculated that the origin of gshB gene of strain CCSYU10100 was from Pseudomonas fluorescens by lateral gene transfer. The deduced amino acid sequence of strain CCSYU10100 contained two conserved domain, i.e., prokaryotic GSH synthetase, N-terminal domain (2^nd～58^th amino acid residues) (identities 44.5%) and rokaryotic GSH synthetase, ATP-binding domain(61^st～221^st amino acid residues) (identities 93.4%). To our knowledge, this is the first report showing gshB gene exists in Lactococcus lactis, even in Gram-positive bacteria.