초록
<P><B>Background</B></P><P>The <I>Bacillus subtilis</I> genome-reduced strain MGB874 exhibits enhanced production of exogenous extracellular enzymes under batch fermentation conditions. We predicted that deletion of the gene for RocG, a bi-functional protein that acts as a glutamate dehydrogenase and an indirect repressor of glutamate synthesis, would improve glutamate metabolism, leading to further increased enzyme production. However, deletion of <I>rocG</I> dramatically decreased production of the alkaline cellulase Egl-237 in strain MGB874 (strain 874∆rocG).</P><P><B>Results</B></P><P>Transcriptome analysis and cultivation profiles suggest that this phenomenon is attributable to impaired secretion of alkaline cellulase Egl-237 and nitrogen starvation, caused by decreased external pH and ammonium depletion, respectively. With NH<SUB>3</SUB>-pH auxostat fermentation, production of alkaline cellulase Egl-237 in strain 874∆rocG was increased, exceeding that in the wild-type-background strain 168∆rocG. Notably, in strain 874∆rocG, high enzyme productivity was observed throughout cultivation, possibly due to enhancement of metabolic flux from 2-oxoglutarate to glutamate and generation of metabolic energy through activation of the tricarboxylic acid (TCA) cycle. The level of alkaline cellulase Egl-237 obtained corresponded to about 5.5 g l<SUP>-1</SUP>, the highest level reported so far.</P><P><B>Conclusions</B></P><P>We found the highest levels of production of alkaline cellulase Egl-237 with the reduced-genome strain 874∆rocG and using the NH<SUB>3</SUB>-pH auxostat. Deletion of the glutamate dehydrogenase gene <I>rocG</I> enhanced enzyme production via a prolonged auxostat fermentation, possibly due to improved glutamate synthesis and enhanced generation of metabolism energy.</P>