Adaptive laboratory evolution induced novel mutations in Zymomonas mobilis ATCC ZW658: a potential platform for co-utilization of glucose and xylose.

A systematic adaptive laboratory evolution strategy was employed to develop a potential Zymomonas mobilis strain with the ability to co-utilize glucose and xylose. Z. mobilis ATCC ZW658, a recombinant xylose fermenting strain, was subjected to adaptive laboratory evolution over a period of 200 days under strict selection pressure of increasing concentration of xylose. The evolved strain exhibited 1.65 times increase in the overall specific xylose utilization rate when compared with the parent strain. Furthermore, the strain displayed significantly improved performance in terms of co-fermentation of xylose in the presence of glucose with specific glucose and xylose utilization rate of 1.24 g g-1 h-1 and 1.34 g g-1 h-1, respectively. Altered phenotypic response of the evolved strain, in terms of improved xylose utilization, co-utilization of mixed sugars, enhanced growth, ethanol production, and reduced xylitol production has been explained by novel mutations, identified using next-generation sequencing, in xylose assimilating, metabolizing, and crucial regulatory pathway genes and key enzyme activity assays.

Regulation of butanol biosynthesis in Clostridium acetobutylicum ATCC 824 under the influence of zinc supplementation and magnesium starvation.

Present study reports modulation in butanol biosynthesis in Clostridium acetobutylicum ATCC 824 under the influence of zinc supplementation or magnesium starvation either individually or in combination. An improvement in butanol titer from 11.83 g L-1 in control to 13.72 g L-1, 15.79 g L-1, and 19.18 g L-1 was achieved when organism was grown on magnesium starved, zinc supplemented and combined zinc supplemented-magnesium starved fermentation medium, respectively. The elevation in butanol biosynthesis was associated with raised glucose utilization, reduced ethanol production and early induction of solventogenesis. Change in these phenotypic traits of the organism may be attributed to multi-level modulation in central carbon metabolism e.g., upregulation of glycolytic pathway; upregulation in thiolase activity; key intermediate enzyme for biosynthesis of acids and solvent; upregulation in the activity of butyrylaldehyde dehydrogenase & butanol dehydrogenase, the enzymes responsible for butanol biosynthesis and downregulation in alcohol dehydrogenase, redirecting carbon flux from ethanol to butanol.

Substrate dependent modulation of butanol to ethanol ratio in non-acetone forming Clostridium sporogenes NCIM 2918.

Present study reports a non-acetone producing Clostridium sporogenes strain as a potential producer of liquid biofuels. Alcohol production was positively regulated by sorbitol and instant dry yeast as carbon and nitrogen sources respectively. Media optimization resulted in maximum butanol and ethanol titer (gL-1) of 12.1 and 7.9 respectively. Depending on the combination of carbon sources, the organism was found to manipulate its metabolism towards synthesis of either ethanol or butanol, thereby affecting the total alcohol titer. Among various dual substrate combinations, glucose-glycerol mixture in the ratio of 60:40 resulted in maximum butanol and ethanol titer (gL-1) of 11.9 and 12.1 respectively with total alcohol productivity of 0.59gL-1h-1. In the mixture, when pure glycerol was replaced with crude glycerol, butanol and ethanol titer (gL-1) of 11.2 and 11.7 was achieved. Hence, the strain shows immense potential for biofuels production using crude glycerol as cheap substrate.

Continuous cultivation of lipid rich microalga Chlorella sp. FC2 IITG for improved biodiesel productivity via control variable optimization and substrate driven pH control.

A novel two-stage continuous heterotrophic cultivation of Chlorella sp. FC2 IITG was demonstrated for enhanced lipid productivity. Initially, effect of control variable e.g. dilution rate and feed stream substrate concentrations on biomass productivity was evaluated. This showed significant variation in biomass productivity from 2.4gL-1day-1 to 11.2gL-1day-1. Further, these control variables were optimized by using multi-nutrient mechanistic model for maximizing the biomass productivity. Finally, continuous production of lipid rich algal biomass was demonstrated in two sequential bioreactors for enhanced lipid productivity. The biomass productivity of 92.7gL-1day-1 was observed in the first reactor which was operated at model predicted optimal substrate concentrations of feed stream. The intracellular neutral lipid enrichment by acetate addition resulted in lipid productivity of 9.76gL-1day-1 in the second reactor. Both the biomass and lipid productivities obtained from current study are significantly high amongst similarly reported literatures.