l-arabonate and d-galactonate production by expressing a versatile sugar dehydrogenase in metabolically engineered Escherichia coli

The production of l-arabonate and d-galactonate employing a versatile l-arabinose dehydrogenase (AraDH) from Azospirillum brasilense is presented. The promiscuity of AraDH is manifested by its appreciable activity towards l-arabinose and d-galactose as substrates, and NAD+ and NADP+ as cofactors. The AraDH was introduced into an engineered Escherichia coli with inactive l-arabinose or d-galactose metabolism, resulting in strains EMA2 and EWG4, respectively. EMA2 produced 43.9 g L−1 l-arabonate with a productivity of 1.22 g L−1 h−1 and 99.1% (mol/mol) yield. After methanol precipitation, 92.6% of l-arabonate potassium salt was recovered with a purity of 88.8%. Meanwhile, EWG4 produced 24.0 g L−1 d-galactonate, which is 36% higher than that of the strain carrying the specific d-galactose dehydrogenase. Overall results reveal that the versatility of AraDH to efficiently catalyze the formation of l-arabonate and d-galactonate could be a useful tool in advancing industrial viability for sugar acids production.