Decreased formation of branched-chain short fatty acids in Bacillus amyloliquefaciens by metabolic engineering.

Objectives: To reduce the unpleasant odor during 1-deoxynojirimycin (DNJ) production, the genes of leucine dehydrogenase (bcd) and phosphate butryltransferase (ptb) were deleted from Bacillus amyloliquefaciens HZ-12, and the concentrations of branched-chain short fatty acids (BCFAs) and DNJ were compared.
Results: By knockout of the ptb gene, 1.01 g BCFAs kg ^-1 was produced from fermented soybean by HZ-12Δptb. This was a 56% decrease compared with that of HZ-12 (2.27 g BCFAs kg ^-1 ). Moreover, no significant difference was found in the DNJ concentration (0.7 g kg ^-1 ). After further deletion of the bcd gene from HZ-12Δptb, no BCFAs was detected in fermented soybeans with HZ-12ΔptbΔbcd, while the DNJ yield decreased by 26% compared with HZ-12.
Conclusions: HZ-12Δptb had decreased BCFAs formation but also maintained the stable DNJ yield, which contributed to producing DNJ-rich products with decreased unpleasant smell.