Low pH D-xylonate production with Pichia kudriavzevii

D-Xylonic acid is one of the top 30 most desirable chemicals to be derived from biomass sugars identified by the US Department of Energy, being applicable as a non-food substitute for D-gluconic acid and as a platform chemical. We engineered the non-conventional yeast Pichia kudriavzevii VTT C-79090T to express a D-xylose dehydrogenase coding gene from Caulobacter crescentus. With this single modification the recombinant P. kudriavzevii strain produced up to 171g L^-1 of D-xylonate from 171g L^-1 d-xylose at a rate of 1.4g L^-1h^-1 and yield of 1.0g [g substrate consumed]^-1, which was comparable with D-xylonate production by Gluconobacter oxydans or Pseudomonas sp. The productivity of the strain was also remarkable at low pH, producing 146g L^-1 D-xylonate at 1.2g L^-1h^-1 at pH 3.0. This is the best low pH production reported for D-xylonate. These results encourage further development towards industrial scale production.