MICROBIAL PLATFORM FOR BIOETHANOL PRODUCTION OF ETHANOL FROM A GREEN ALGAE POLYSACCHARIDE, ULVAN

With an ever increasing energy demand and concerns of dependence on fossil fuels, the current interest in new sustainable sources of energy has turned our attention towards an underexploited biomass rich in carbohydrates, the green macroalgae Ulva sp., which shows great promise as an alternative feedstock for high yield biofuel production. The ultimate objective of this research is to optimize enzymatic machinery required for complete saccharification of the Ulva sp. polysaccharide, ulvan, and construct pathways in bacteria capable of metabolizing the depolymerized sugars into ethanol, a system called consolidated bioprocessing (CBP).

Using techniques in bioinformatics and metabolic engineering, we have identified and cloned novel enzymes involved in ulvan degradation and constructed an operon with RBS modulated genes for optimal utilization and fermentation of L-rhamnose, the dominant monomer of ulvan. Here we characterize the activity of two newly discovered ulvan lyases, enzymes which catalyze the first endolytic cleavage in the ulvan polysaccharide chain, as well as two members of an unsaturated β-glucuronyl hydrolase enzyme family, which degrade the products of ulvan lyase, later allowing for the release of rhamnose and other monosaccharides for fermentation. Fermentation performance of the rhamnose-utilizing bacterial strain was assessed under anaerobic conditions, where cultures were incubated for 6 days in 37°C and sampled every 24h to measure optical density and to quantify sugar and fermentation metabolites using HPLC. We report an overall 84% improvement in ethanol production and 96% improvement in ethanol yield on L-rhamnose (at 120h), as compared to the control strain. The above results represent our biofuel group’s progress in the construction of a bacterial platform in which both degradation of ulvan and fermentation to ethanol will be implemented.