Efficient homofermentative L-(+)-lactic acid production from xylose by a novel lactic acid bacterium, Enterococcus mundtii QU 25

Abstract

Enterococcus mundtii QU 25, a newly isolated lactic acid bacterium, efficiently metabolized xylose into l-lactate. In batch fermentations, the strain produced 964 mM l-(+)-lactate from 691 mM xylose, with a yield of 1.41 mol/mol xylose consumed and an extremely high optical purity of ≥99.9% without acetate production.

FIG. 1.

Profiles of lactate fermentation with xylose by Enterococcus mundtii QU 25. Fermentations were conducted in a 1-liter jar fermentor with a 0.4-liter working volume at 43°C, pH 7.0, and 200 rpm. The initial xylose concentrations were 334 mM (A), 480 mM (B), and 691 mM (C). Symbols: open circles, xylose concentration; closed circles, lactate concentration; open triangles, acetic acid concentration; closed triangles, formic acid concentration; open squares, ethanol concentration; closed squares, dry cell weight. Data points represent the means and standard deviations of results from 3 independent experiments. The standard deviation is less than that corresponding to the size of the symbol if no error bars are seen.