Background Acetoin (AC) is a vital platform chemical widely used in food, pharmaceutical and chemical industries. With increasing concern over non-renewable resources and environmental issues, using low-cost biomass for acetoin production by microbial fermentation is undoubtedly a promising strategy. Results This work reduces the disadvantages of Bacillus subtilis during fermentation by regulating genes involved in spore formation and autolysis. Then, optimizing intracellular redox homeostasis through Rex protein mitigated the detrimental effects of NADH produced by the glycolytic metabolic pathway on the process of AC production. Subsequently, multiple pathways that compete with AC production are blocked to optimize carbon flux allocation. Finally, the population cell density-induced promoter was used to enhance the AC synthesis pathway. Fermentation was carried out in a 5-L bioreactor using bagasse lignocellulosic hydrolysate, resulting in a final titer of 64.3 g/L, which was 89.5% of the theoretical yield. Conclusions The recombinant strain BSMAY-4-PsrfA provides an economical and efficient strategy for large-scale industrial production of acetoin.

An efficient ammonia nitrogen degrading bacterial strain was isolated from a fish and shrimp pond and identified as Bacillus subtilis (Ab03). Firstly, the strain was continuously domesticated in ammonium solution to improve its nitrogen removal capacity. The performance of the strain in terms of nitrogen removal efficiency under different culture conditions was then examined. Finally, the nitrogen removal process and related strain mechanisms were analyzed by nitrogen balance. The results showed the strain Ab03 could remove 91.67% of NH 4 + -N at 300 mg/L under the conditions of glucose as the single carbon source, C/N of 15, pH of 7.5, the temperature of 35 ℃ and dissolved oxygen of 7-8 mg/L. It was also found that under conditions where ammonia nitrogen was the only nitrogen source, strain Ab03 could also undergo aerobic denitrification for simultaneous conversion, with a final gas conversion rate of 74.81%.

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