Poly-γ-glutamic acid production of Bacillus subtilis (natto) in the absence of DegQ: A gain-of-function mutation in yabJ gene
Published on Dec 1, 2019in Journal of Bioscience and Bioengineering2.032
· DOI :10.1016/j.jbiosc.2019.05.014
Poly-γ-glutamic acid (γPGA) production by Bacillus subtilis is regulated by the quorum sensing system where DegQ transmits the cell density signal to a DNA-binding protein DegU. A mutation suppressing the γPGA-negative phenotype of degQ gene knock-out mutant (Δ degQ ) was identified through whole genome sequencing. The mutation conferred an amino acid substitution of Ser103 to phenylalanine (S103F) in yabJ that belongs to the highly conserved YjgF/YER057c/UK114 family. Genetic experiments including LacZ-fusion assay of γPGA synthetic operon confirmed that the suppressor mutation ( yabJ S103F ) was responsible for the recovery of γPGA production. The yabJ itself was not essential for the γPGA production and the mutant allele enabled γPGA production of the Δ degQ strain even in the presence of wild type yabJ . Thus, yabJ S103F was a dominant positive allele. degU-lacZ fusion gene was hyper-expressed in cells carrying the yabJ S103F , but disruption of yabJ did not affect the transcription level of the degU-lacZ . These observations suggested that YabJ acquired a function to stimulate expression of degU by the S103F mutation which is involved in the regulation of γPGA synthesis.