BACTERIAL METABOLIC ENGINEERING FOR BIOETHANOL PRODUCTION FROM Ulva lactuce

The demand for biofuel as energy source has been rising. The green macroalgae Ulva lactuca, is an attractive and environmentally sustainable alternative energy source [1]. We intend to create a microbial platform capable of degrading Ulva’s main polysaccharides, ulvan, and ferment its simple sugars (rhamnose, glucuronic acid, glucose and xylose), by using metabolic engineering and consolidating bioprocessing. Three deletion mutations were introduced into Escherichia coli KO11, creating MAK1, in order to block the competitive fermentation pathways for lactate and acetate production and lead the fermentation process mainly to the production of ethanol. In order to increase the level of ethanol produced by rhamnose fermentation we constructed an RBS modulated operon. This was achieved by assembling combinatorial library of operons, in which each variant contains the same order of 5 chosen genes, involved in the rhamnose fermentation process, but with different combination of RBS sequences that differ in their binding affinity [2]. Initial screening for fermentation performance of 18 rhamnose utilizing strains, compared to the control strain, revealed the strain MAK1/pLC1964 exhibiting 120% improvement in ethanol yield. Screening of additional strains is underway. By improving and optimizing the utilization operon of rhamnose, we hope to achieve an economically viable platform for bioethanol production.

References:

1. van der Wal, H. et al. Production of acetone, butanol, and ethanol from biomass of the green seaweed Ulva lactuca. Bioresour. Technol. 128, 431–437 (2013).
2. Zelcbuch, L. et al. Spanning high-dimensional expression space using ribosome-binding site combinatorics. Nucleic Acids Res. 41, e98 (2013).