Recent synthetic biology and metabolic engineering approaches for enhancing free fatty acid production in Escherichia coli.

The first-generation fuels such as corn-based ethanol and plant oil derived-biodiesel are the well-known alternatives to petroleum-derived fuels to reduce the greenhouse gases and global warming effects. Though they offer several advantages, their usage are limited because of various issues such as problems in commercialization, non-sustainability in production, need of large amounts of raw materials (vegetable or seed oil) in the case of biodiesel, limited land yield, and reliance on coal-derived co-substrate (methanol) for transesterification, existing petrochemical and automotive infrastructures. Other microbial biofuels such as fatty acid-derived fuel molecules including free fatty acids, fatty esters offering some unique advantages as compared with other fuel supplements have gained great attention from scientific group to develop new microbial platforms through metabolic engineering, synthetic biology, protein engineering, metabolomics, transcriptomics to produce fatty acid-derived fuel molecules at high yield and productivity for commercial exploitation. In vivo, free fatty acids (FFAs) can be used as precursors for the production of valuable fuels, polymer additives and industry chemicals by various catalytic reactions. Since the microorganism such as Escherichia coli synthesize fatty acids which are mainly used to form lipids for cell membrane constitution, FFAs are not normally accumulated as intermediates. Fatty acid metabolism is tightly regulated at transcriptional and post-transcriptional levels by both the transcription factor and product inhibition, meaning that fatty acid overproduction may require extensive re-engineering of cellular metabolism. Therefore, we here present the recent efforts to enhance FFA production via metabolic engineering and synthetic biology with special reference to E. coli