Title: Effects of lactic acid bacteria contamination on lignocellulosic ethanol fermentation Authors
Submitted to: American Society for Microbiology General Meeting
Publication Type: Abstract Only
Publication Acceptance Date: May 21, 2013
Publication Date: N/A
Technical Abstract: Slower fermentation rates, mixed sugar compositions, and lower sugar concentrations may make lignocellulosic fermentations more susceptible to contamination by lactic acid bacteria (LAB), which is a common and costly problem to the corn-based fuel ethanol industry. To examine the effects of LAB contamination on lignocellulosic fermentations, a bacterial strain (Escherichia coli FBR5) engineered for fermentation of pentose and hexose sugars was used as microbial catalyst in shake-flask fermentations experimentally infected with Lactobacillus fermentum. In phosphate-buffered Luria broth (LB) supplemented with 2% (w/v) each of glucose and arabinose, cultures challenged with L. fermentum consumed all the sugar but produced 7% less ethanol than uninfected controls. In LB media containing 4% (w/v) glucose and 4% (w/v) xylose, ethanol yield was 29% less than uninfected controls. Cultures did not fully consume the xylose, although limited buffering capacity of the media may have also contributed to the poorer performance. In fermentations of an acid hydrolysate of corn fiber, neither uninfected controls nor challenged cultures went to completion within 72 h, but ethanol yields in the LAB-challenged cultures were reduced by 15%. While glucose and xylose consumption were the same, the challenged cultures showed an increase in consumption of arabinose, which was marked by an increase in lactic and acetic acid fermentation products. This work demonstrates that lignocellulosic substrates provide a favorable environment for growth of contaminating LAB species, emphasizing the need for effective contamination control methods during lignocellulosic ethanol production.