Genomics Perspectives of Bioethanol Producing Zymomonas Mobilis

Background

In the present 21^st century, there has been ever-increasing demand for the fuel in particularly bioethanol. The various causes for the increase in demand for the fuel are as follows: 1) The depletion of the available energy resources such as fossil fuel, lignite, coal; 2) increase in pollution level and global warming; 3) rapid urbanization; 4) lack of manpower and technologies in the developing countries to tap solar, wind and tidal energy. Thus, these sources of energy are non-renewable when compared to bioethanol. Ethanol production from food crops like corn is mostly dependent upon fuel subsidies and it consumes food crop to produce biofuel. Moreover, the retail price for commercial microbial ethanol is 2.62 US $ /gallon compared to a gallon of gasoline priced at 3.03 dollar. Bioethanol is an ideal candidate in the current scenario because of its potential application as fuel, beverage, feedstock, antiseptic and industrial solvent. The major steps for large-scale microbial production of ethanol are fermentation of sugars, distillation, and dehydration. Z. mobilis has been known to have favourable traits like limited growth requirements, genetically amenable, higher sugar, and ethanol tolerance. The primary focus of this chapter is to review the current developments in the field of functional genomics and bioinformatics analysis of the genome of Z. mobilis.

During the pregenomic era, there was considerable amount of research focused upon substrates optimization for ethanol fermentation process, genetic engineering of strains. Gunasekaran et al. (1986) demonstrated production of bioethanol by 4 different strains of Z. mobilis by using natural substrates like cane juice and molasses. Kamini and Gunasekaran (1987, 1989) has shown that synchronized ethanol production from lactose by strains of Z. mobilis 1960, B 4286 by coculturing with K. fragilis 665. Gunasekaran and Kamini (1991) demonstrated elevated ethanol production from lactose by immobilized cells of Z. mobilis B 4286 cocultured with K. fragilis 665. Nellaiah et al. (1988a) has reported the production of 94.0 g l^-1, 76.9 g l^-1, and 66.5 g l^-1 of ethanol at glucose, fructose, and sucrose concentrations of 200 g l^-1, respectively by Z. mobilis B-4286. Nellaiah et al. (1988b) has reported the production of 80.0 g l^-1 of ethanol from enzymatically hydrolysed cassava starch at glucose concentrations of 171 g l^-1, by Z. mobilis B-4286. Nellaiah and Gunasekaran (1992) showed that highest ethanol concentration of 59 g l^-1 and productivity of 3.57 g l^-1 could be obtained from cassava starch hydrolysate by immobilized Z. mobilis. Amutha and Gunasekaran (1994) showed that concurrent saccharification and fermentation of cassava starch using Z. mobilis produced 57 g l^-1 of ethanol. Baratti et al. (1991) has demonstrated that Z. mobilis possess an extracellular sucrase which is mainly responsible for sucrose hydrolysis during fermentation. Kannan et al. (1998) has shown that improved ethanol production of 73.5 g l^-1 from 150 g l^-1 sucrose by a mutant of Z. mobilis than of its parent strain, B-806 (65.2 g l^-1).