Expression of degQ gene and its effect on lipopeptide production as well
as the formation of secretory proteases in Bacillus subtilis strains
Abstract
Bacillus subtilis is described as a promising production strain for
lipopeptides. In the case of B. subtilis strains JABs24 and DSM10T,
surfactin, and plipastatin are produced. Lipopeptide formation is
controlled, among others, by the DegU response regulator. The activating
phospho-transfer by the DegS sensor kinase is stimulated by the
pleiotropic regulator DegQ, resulting in enhanced DegU activation. In B.
subtilis 168, a point mutation in the degQ promoter region leads to a
reduction in gene expression. Corresponding reporter strains showed a
14-fold reduced expression. This effect on degQ expression and the
associated impact on lipopeptide formation was examined for B. subtilis
JABs24, a lipopeptide-producing derivative of strain 168, and B.
subtilis wild-type strain DSM10T, which has a native degQ expression.
Based on the stimulatory effects of the DegU regulator on secretory
protease formation, the impact of degQ expression on extracellular
protease activity was additionally investigated. To follow the impact of
degQ, a deletion mutant was constructed for DSM10T, while a natively
expressed degQ version was integrated into strain JABs24. This allowed
strain-specific quantification of the stimulatory effect of degQ
expression on plipastatin and the negative effect on surfactin
production in strains JABs24 and DSM10T. While an unaffected degQ
expression reduced surfactin production in JABs24 by about 25%, a
6-fold increase in plipastatin was observed. In contrast, degQ deletion
in DSM10T increased surfactin titer by 3-fold but decreased plipastatin
production by 5-fold. In addition, although significant differences in
extracellular protease activity were detected, no decrease in
plipastatin and surfactin produced during cultivation was observed.