Molecular and functional evidence of phosphatidylserine synthase in Vibrio parahaemolyticus.

Phosphatidylserine synthase (Pss) catalyzes phosphatidylserine synthesis, which is critical to synthesizing the component of cell membrane. However, few putative pss genes of bacteria have been studied. In this study, it was found that Vibrio parahaemolyticus, a common foodborne pathogen that causes human gastroenteritis, has a type I Pss with two HKD motifs and is a phospholipase D superfamily member. The transcriptional start site of pss was mapped through sequencing and was identified at -37 nucleotides upstream of the start codon. Pss mRNA was found to be expressed mainly during the exponential phase. In addition, the promoter was identified using a lux reporter assay and gel shift assay with an RNA polymerase. To analyze the catalytic activity, a soluble form of His -tagged recombinant Pss was overexpressed and purified from Escherichia coli. Using matrix-assisted laser desorption ionization-time of flight mass spectrometry, it was found that Pss can catalyze cytidine diphosphate diacylglycerol and L-serine to form phosphatidylserine. Since Pss is conserved in vibrios, the current study can promote understanding the biosynthesis of phospholipid in Vibrio bacteria that might cause vibriosis. This is the first report of molecular characterization of the pss gene and identification of Pss enzyme activity in V. parahaemolyticus using matrix-assisted laser desorption ionization time-of-flight mass spectrometry.