Coculture of Gluconobacter oxydans and Escherichia coil for 3,4-Dihydroxybutyric Acid Production from Xylose

3,4-Dihydroxybutyric acid (3,4-DHBA) is an important platform chemical with versatile applications. Traditional chemical approaches for 3,4-DHBA production involving hazardous materials and harsh reaction conditions are environmentally unfriendly. The reported biotechnological routes for 3,4-DHBA production rely on microbial monocultures with low productivity and yield. In this study, a coculture system to synthesize 3,4-DHBA from xylose was established using Gluconobacter oxydans and Escherichia coli. First, it was confirmed that G. oxydans 621H can oxidize xylose and 3,4-dihydroxybutanal (3,4-DHB) into xylonate and 3,4-DHBA, respectively. Second, xylonate dehydratase and alpha-ketoisovalerate decarboxylase were overexpressed and the competing pathways in the host strain were knocked out for 3,4-DHB biosynthesis from xylonate in E. coli. Third, the conditions for the coculture of G. oxydans 621H and engineered E. coli were optimized to enhance 3,4-DHBA biosynthesis from xylose. Finally, the coculture system produced 3.26 g/L 3,4-DHBA from 7.0 g/L xylose with a high yield of 0.47 g/g, achieving the highest titer and yield of 3,4-DHBA reported so far. Besides the biotechnological production of 3,4-DHBA, the coculture of G. oxydans 621H with engineered E. coli would be a useful engineering strategy in the production of other important biochemicals.