Exploration of Various Microbial Systems for the Biofuel Production

Fuels on a broad scale are divided into two categories based on their renewability, i.e., renewable and non-renewable. The increasing scarcity, prices of fossil fuels, and the constantly increasing level of CO2 in the environment have led to an immediate need to investigate alternative fuels. Microorganisms are extensively being used for the generation of biofuels. The qualities of E. coli to be accessible to culture and maintenance have made it stand out among the microbes. Their ability to metabolize pentoses further draws it near to being used for biofuel production. Fermentative bacteria, particularly the class clostridia (obligate anaerobe), have been successful hydrogen producers. Dark fermentation employed by clostridia has dual advantages, i.e., production of biohydrogen and waste reduction since clostridia can utilize a broad range of substrates, including organic wastes. Moreover, the application of metabolic engineering can provide additional processes to clostridia required for the efficient production of biobutanol. The review further explores the two yeast systems, conventional and non-conventional systems. Synthetic biology tools have explored the traditional system, which comprises Saccharomyces cerevisiae for commercial purposes. The non-conventional yeast system has several advantages over the conventional ones, like ethanol tolerance, thermotolerance, inhibitor tolerance, and genetic diversity. However, the application of synthetic biology tools is still being explored in microbes like E. coli, Clostridia species, Saccharomyces cerevisiae, and Yarrowia lipolytica. The review also incorporates excellent commercial strain features like economical fuel tolerance, inhibitor tolerance, and thermotolerance control on redox balance and yield increases. The main focus is to bridge the gap between lab-scale production and commercialization.