Chitin degradation and its effect on natural transformation: a systematic genetic study in Vibrio parahaemolyticus

The degradation of polymeric chitin by chitinase liberates soluble N-acetyl glucosamine oligosaccharides (GlcNAc_n≥2), a source of nutrition that can also induce a state of natural genetic competence in Vibrio parahaemolyticus. This analysis revealed that among seven predicted chitinases, the synergistic action of VPA0055 (ChiA2), VP0619 (ChiB), and VPA0832 (Cdx) were essential for the robust growth and high transformation frequency on chitin. The endochitinase, ChiA2, and periplasmic chitinase, Cdx were indispensable for chitin degradation. ChiB was not essential for growth on chitin but did have an effect on the rate of chitin degradation. Interestingly, the loss of Cdx drastically reduced growth on insoluble chitin, but growth on soluble GlcNAc_5/6 remained same. The utilization of GlcNAc_5/6 was only inhibited when there was mutation of Cdx with the other periplasmic chitinases VP0755 and VP2486. This suggests that Cdx might also be involved in extracellular degradation of chitin, in addition to its role as a periplasmic chitinase. Moreover, the periplasmic chitin oligosaccharide-binding protein (CBP) was found to be essential for the efficient utilization of chitin. The CBP was specifically needed for the processing of GlcNAc_4-6 during growth on chitin. Overall, this study provides detailed analysis of the machinery behind chitin degradation in V. parahaemolyticus.