General and Specific Stress Responses Towards Short Even-Chain Alcohols in Lactic Acid Bacteria Provide Clues for Improving Second Generation Biorefineries

Metabolic Engineering Conference
Vancouver June 15th â?? 19th
Lactic acid bacteria (LAB) have the potential to become efficient production organisms for large-scale bio-refinery processes. LAB are currently used extensively by the dairy industry for fermentation of milk; thus their industrial importance is indisputable. The biotechnological exploitation of LAB has multiple benefits. Firstly, LAB possess high glycolytic capacities, with up to 20% of the total proteome consisting of glycolytic enzymes, turning glycolysis into a metabolic highway (Guillot et al., 2003). Secondly, many LAB use a homofermentative metabolism, converting more than 90% of their pyruvate into a single product, lactate. Re-routing of this major flux into alternative fermentation products, such as small-chain alcohols opens for the opportunity of producing such potential bio-alcohols at high yields. Since LAB primarily produce lactate, they have evolved a tolerance towards acidic environments, through a multi-stress resistance mechanism, resulting in slightly elevated resistance towards a wide range of harsh chemicals. Last, but not least, many LAB can us alternative carbon source of no use as food for humans or as feed for domestic animals, opening for the possibility of producing 2nd generation biofuels.
A major problem facing the biotechnological exploitation of LAB for the production of high value products such as higher alcohols is related to the toxicity of these compounds, and the lack of knowledge about their effects. Studies in LAB stress responses have until now focused on oxidative, osmotic, nutritional, temperature, and pH stresses (Tsakalidou & Papadimitriou, 2011).
In this study, we have characterized the stress response of Lactococcus lactis subspecies cremoris strain MG1363 towards the exogenous short even-chain alcohols; ethanol, n-butanol and 1-hexanol. A detailed physiological, metabolic, and comparative transcriptional analysis, provided valuable insights into the stress response of LAB towards these alcohols and gave clues to potential targets for improvement of L. lactis alcohol tolerance. We found that the stress response towards the three alcohols showed both common response patterns as well as patterns that separated ethanol stress from n-butanol/1-hexanol stress.

Guillot, A., Gitton, C., Anglade, P., & Mistou, M.-Y. (2003). Proteomic analysis of Lactococcus lactis, a lactic acid bacterium. Proteomics, 3(3), 337â??354. doi:10.1002/pmic.200390047

Tsakalidou, E., & Papadimitriou, K. (2011). Stress Response of Lactis Acid Bacteria.