Metabolic engineering of the marine bacteria Neptunomonas concharum for the production of acetoin and meso-2,3-butanediol from acetate

The marine bacteria Neptunomonas concharum was firstly characterized in 2012 and grew optimally at 37 °C, whereas the other species of Neptunomonas showed a lower range of temperature to grow. In this study, we described the achievement of metabolic engineering of N. concharum for the synthesis of acetoin and meso-2,3-butanediol. First, a series of carbon sources were used to cultivate N. concharum. Acetate and succinate were found to be suitable substrates to support effective cell growth. Second, a general electransformation procedure was developed. The optimized transformation efficiency reached about 3 × 103 cfu/μg DNA. Third, the heterologous acetoin and meso-2,3-butanediol biosynthesis pathway was functionally expressed in N. concharum. In shake flask cultivation, the titers of acetoin and meso-2,3-butanediol reached 0.11 g/L. Finally, malic enzyme was overexpressed to improve intracellular pyruvate availability, which significantly improved acetoin and meso-2,3-butanediol titers to 0.56 g/L and 0.38 g/L, respectively. Our results demonstrate that N. concharum has a promising potential to manufacture bulk chemicals using acetate as the carbon source.