S40: Why lactic acid bacteria for biobutanol?

The Gram-positive Lactic acid bacteria (LAB) are considered attractive biocatalysts for biomass to biofuels for several reasons. They have GRAS (Generally Recognized As Safe) status that are acceptable in food, feed and medical applications.  LAB are fermentative: selected strains are capable of fermenting multiple sugars simultaneously and converting diversified substrates into various products; LAB are adaptive: capable of growth in lower or higher pHs, at a temperature range from 30^oC-50^oC.  Most importantly, LAB can tolerate and grow in media supplemented with up to 3-4% butanol.

Butanol has been recognized as a superior transportation fuel since it is energy dense than ethanol and it can be used directly as a drop-in fuel without engine modification.  Biologically, butanol is produced through anaerobic fermentation by Clostridia cultures. However, the overall economics for commercial butanol fermentation remains uncertain.  Major hurdles include low fermentation efficiency with cheaper lignocellulosic feedstocks and high toxicity of butanol to its producing strains. The increased butanol concentrations (less than 2%) in a butanol fermentation bioreactor, albeit desired for cost-effective product recovery, often lead to reduced growth and eventually death of the producing Clostridium cells.  Suitable microbial hosts to be used for metabolic engineering strategies for butanol production must be able to tolerate higher titers of butanol in order to improve yields.  The butanol tolerant LAB strains need to be tested as potential hosts for manipulations toward efficient conversion of biomass to butanol. Results of using genetic engineering tools to modify selected LAB strains for butanol production will be presented.