| Summary: | Bovine Escherichia coli infection, which causes major economic losses to the cattle industry each year, can be prevented by administering
formalin-inactivated vaccine. However, to enhance the application of this vaccine, the cell density of the formalin-inactivated E. coli should
be boosted. This can be achieved by reducing the accumulation of acetate, a primary inhibitory metabolite in E. coli fermentation. To this
end, the present study investigated the effect of pH, dissolved oxygen (DO) levels, and feeding methods on bovine E. coli fermentation,
and developed two-stage pH and DO control strategies and a combined pH- and DO-mediated feeding strategy for the fermentation. The
optimized conditions for Bovine E. coli were pH 7.0 at 0-10 h, 6.5 at 10-24 h; DO 50% at 0-10 h, 30% at 10–24 h; pH and DO feedback feeding
at 0-10 h and 10-24 h, respectively. With Bovine E. coli fermentation under the optimized conditions, the acetate accumulation was 1.12 g/L
and the cell density was 36.47 (OD600), which were 59.12% lower and 77.29% higher than these with the original conditions (pH 7.0; DO
20%; residual glucose concentration maintained at 2.0 g/L). After analyzing the main nodes of acetate synthesis, it was found that the lower
carbon flux enters the Embden-Meyerhof pathway. Under the optimized conditions, the pyruvate flux and acetyl-CoA synthesis were low,
and much of the acetyl-CoA participated in the tricarboxylic acid cycle. The extracellular acetate flux was 8.3%, which was 65.13% lower than
in the original conditions.
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