Production of l-arabinonic acid from l-arabinose by the acetic acid bacterium Gluconobacter oxydans

l-Arabinonic acid is a five carbon sugar acid valuable for various potential applications. Based on previous observations that Gluconobacter oxydans 621H oxidizes l-arabinose in the periplasm by the membrane-bound glucose dehydrogenase GdhM yielding l-arabinonic acid, we tested its ability for production. In fed-batch shake flasks without pH control, 17.4 g/L l-arabinonic acid and 5.7 g/L l-arabino-1,4-lactone were obtained. A large fraction of l-arabinose remained unused since acidification of the medium prevented further substrate oxidation. In pH 6-controlled fed-batch bioreactors, up to 120 g/L l-arabinonic acid and 13 g/L l-arabino-1,4-lactone could be obtained with strain 621H (144 h). Constitutive overexpression of gdhM did not increase product titers and resulted in reduced biomass formation, yet the gdhM overexpression strain showed higher biomass-specific production (169 g/L/g_cdw) compared to 621H (131 g/L/g_cdw). The high combined product titer (133 g/L, 814 mM) makes G. oxydans a very promising host for high-level production of l-arabinonic acid.