Introduction of bifunctional alcohol/acetaldehyde dehydrogenase gene (adhE) in Fructobacillus fructosus settled its fructophilic characteristics

Fructophilic lactic acid bacteria (FLAB) are unique in the sense that they prefer D-fructose over D-glucose as main carbon source. If D-glucose is metabolised, electron acceptors are required and significant levels of acetate are produced. These bacteria are found in environments rich in D-fructose, such as flowers, fruits and the gastrointestinal tract of insects feeding on fructose-rich diets. Fructobacillus spp. are representatives of this unique group, and their fructophilic characteristics are well conserved. In this study, the bifunctional alcohol/acetaldehyde dehydrogenase gene (adhE) from Leuconostoc mesenteroides NRIC 1541^T was cloned into a plasmid and transferred to Fructobacillus fructosus NRIC 1058^T. Differences in biochemical characteristics between the parental strain (NRIC 1058^T) and the transformants were compared. Strain 1-11, transformed with the adhE gene, did not show any fructophilic characteristics, and the strain grew well on D-glucose without external electron acceptors. Accumulation of acetic acid, which was originally seen in the parental strain, was replaced with ethanol in the transformed strain. Furthermore, in silico analyses revealed that strain NRIC 1058^T lacked the sugar transporters/permeases and enzymes required for conversion of metabolic intermediates. This may be the reason for poor carbohydrate metabolic properties recorded for FLAB.