Improved production of secreted heterologous enzyme in Bacillus subtilis strain MGB874 via modification of glutamate metabolism and growth conditions
- Equal contributors
1 Biological Science Laboratories, Kao Corporation, 2606 Akabane, Ichikai, Haga, Tochigi 321-3497, Japan
2 Graduate School of Biological Science, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0101, Japan
3 Analytical Science Laboratories, Kao Corporation, 2606 Akabane, Ichikai, Haga, Tochigi 321-3497, Japan
4 Medical Mycology Research Center, Chiba University, 1-8-1 Inohana, Chuo-ku, Chiba 260-8673, Japan
5 Graduate School of Information Science, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0101, Japan
6 Fundamental Technology Research Laboratories, Kao Corporation, 623 Zi Ri Rd, Minhang Dist, Shanghai 200241, China
Microbial Cell Factories 2013, 12:18 doi:10.1186/1475-2859-12-18Published: 18 February 2013
The Bacillus subtilis 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 rocG dramatically decreased production of the alkaline cellulase Egl-237 in strain MGB874 (strain 874∆rocG).
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 NH3-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-1, the highest level reported so far.
We found the highest levels of production of alkaline cellulase Egl-237 with the reduced-genome strain 874∆rocG and using the NH3-pH auxostat. Deletion of the glutamate dehydrogenase gene rocG enhanced enzyme production via a prolonged auxostat fermentation, possibly due to improved glutamate synthesis and enhanced generation of metabolism energy.