Bioenergy: Sustainable fuels from biomass by yeast and fungal whole-cell biocatalysts

The dependency on depleting natural resources is a challenge for energy security that can be potentially answered by bioenergy. Bioenergy is derived from starchy and lignocellulosic biomass in the form of bioethanol or from vegetable oils in the form of biodiesel fuel. The acid and enzymatic methods have been developed for the hydrolysis of biomass and for transesterification of plant oils. However, acid hydrolysis results in the production of unnatural compounds which have adverse effects on yeast fermentation. Recent advancements in the yeast cell surface engineering developed strategies to genetically immobilize amylolytic, cellulolytic and xylanolytic enzymes on yeast cell surface for the production of fuel ethanol from biomass. Whereas in the case of biodiesel fuel production, alkali catalysis gives high levels of conversion in short reaction times. But complexity in the separation of produced biodiesel fuel from glycerol by-product led to intensive research on lipase enzyme and immobilized whole-cell biocatalysts. This system facilitates the easy separation of glycerol with the advantage of cost effectiveness. This review gives an insight in to the recent technological developments in the production of bioenergy, i.e., bioethanol and biodiesel fuel using surface engineered yeast and whole-cell biocatalysts.