Abstract
Background
Poly-γ-glutamic acid (γ-PGA) is a natural anionic biopolymer widely used in various fields, including medicine, food, cosmetics, and environmental protection. The γ-PGA synthase complex, CapBCA, is the only polyprotein complex responsible for γ-PGA synthesis. However, systematic and in-depth research on the function of each component involved in γ-PGA synthesis is scarce, which limits enhanced production of γ-PGA.
Results
To address this limitation, γ-PGA synthase components were localized, and their functions associated with γ-PGA synthesis were investigated in Corynebacterium glutamicum. Bioinformatics analysis and confocal microscopic observations of CapB-sfGFP, CapC-sfGFP, and CapA-sfGFP proteins revealed that γ-PGA synthase components CapB, CapC, and CapA were all localized on the cell membrane. More importantly, γ-PGA was detected only when CapB, CapC, and CapA were expressed in combination in C. glutamicum. Furthermore, enhancement of CapB or CapC transcription levels (from low to high) and maintaining medium-level CapA transcription led to 35.44% and 76.53% increase in γ-PGA yield (γ-PGA yield-to-biomass), respectively. However, maintaining medium-level CapB and CapC transcription, and moderate enhancement of CapA transcription level (from low to medium) led to 35.01% increase in γ-PGA yield, whereas a further increase in CapA expression (from medium to high) led to 10.36% decrease in γ-PGA yield. Notably, CapC had the greatest influence (accounting for 68.24%) on γ-PGA synthesis.
Conclusions
The present study determined the membrane localization of γ-PGA synthase components, CapB, CapC, and CapA, in C. glutamicum and confirmed the significance of these components in γ-PGA production. Furthermore, CapC was found to have the greatest influence on controlling γ-PGA synthesis. These findings shed light into the effect of γ-PGA synthase component expression on γ-PGA synthesis, and provide insights for further improvement in γ-PGA production.
Mutation of genes for cell membrane synthesis in Corynebacterium glutamicum causes temperature-sensitive trait and promotes L-glutamate excretion
