The physiological or molecular factors in C. bescii that may regulate extracellular transport of excess pyruvate or intracellular conversion into acetoin are not clear. However, acetoin production is up to fivefold higher at suboptimal growth temperatures, ranging from 2.6 mM at 60°C to 0.6 mM at 75°C in the parent strain (Fig. 2b). Consistent with this observation, 2,3-BDO production was elevated at 60°C and 65°C in the engineered strains after 72 h of growth