Optimization of the purine operon and energy generation in Bacillus amyloliquefaciens for guanosine production.

Objectives: To deregulate the purine operon of the purine biosynthetic pathway and optimize energy generation of the respiratory chain to improve the yield of guanosine in Bacillus amyloliquefaciens XH7.

Results: The 5'-untranslated region of the purine operon, which contains the guanine-sensing riboswitch, was disrupted. The native promoter Pw in B. amyloliquefaciens XH7 was replaced by different strong promoters. Among the promoter replacement mutants, XH7purE::P41 gave the highest guanosine yield (16.3 g/l), with an increase of 23% compared with B. amyloliquefaciens XH7. The relative expression levels of the purine operon genes (purE, purF, and purD) in the XH7purE::P41 mutant were upregulated. The concentration of inosine monophosphate (IMP), the primary intermediate in the purine pathway, was also significantly increased in the XH7purE::P41 mutant. Combined modification of the low-coupling branched respiratory chains (cytochrome bd oxidase) improved guanosine production synergistically. The final guanosine yield in the XH7purE::P41△cyd mutant increased by 41% to 19 g/l compared with B. amyloliquefaciens XH7.

Conclusion: The combined modification strategy used in this study is a novel approach to improve the production of guanosine in industrial bacterial strains.