No abstract

The enhancement of the biomass productivity of Escherichia coli cells harbouring the truncated 903 bp gene designated as glycoside hydrolase family 43 (GH43) from Clostridium thermocellum showing hemicellulase activity along with its further use in simultaneous saccharification and fermentation (SSF) process is described. (Phosphoric acid) H(3)PO(4)-acetone treatment and ammonia fibre expansion (AFEX) were the pretreatment strategies employed on the leafy biomass of mango, poplar, neem and asoka among various substrates owing to their high hemicellulose content. GH43 showed optimal activity at a temperature of 50 °C, pH 5.4 with stability over a pH range of 5.0-6.2. A 4-fold escalation in growth of the recombinant E. coli cells was observed when grown using repeated batch strategy in LB medium supplemented with glucose as co-substrate. Candida shehatae utilizing pentose sugars was employed for bioethanol production. AFEX pretreatment proved to be better over acid-acetone technique. The maximum ethanol concentration (1.44 g/L) was achieved for AFEX pretreated mango (1%, w/v) followed by poplar with an ethanol titre (1.32 g/L) in shake flask experiments. A 1.5-fold increase in ethanol titre (2.11 g/L) was achieved with mango (1%, w/v) in a SSF process using a table top 2-L bioreactor with 1 L working volume.

This paper proposes a hybrid energy system consisting of wind, photovoltaic and fuel cell designed to supply continuous power to the load. A simple and economic control with dc-dc converter is used for maximum power point tracking and hence maximum power extraction from the wind turbine and photovoltaic array. Due to the intermittent nature of both the wind and photovoltaic energy sources, a fuel cell is added to the system for the purpose of ensuring continuous power flow. The fuel cell is thus controlled to provide the deficit power when the combined wind and photovoltaic sources cannot meet the net power demand. In worst environmental conditions, when there is no output power from the wind or photovoltaic sources, the fuel cell will operate at its rated power of 10 kW. Hence this system under any operating condition will ensure a minimum power flow of 10 kW to the load. This hybrid system allows maximum utilization of freely available renewable energy sources like wind and photovoltaic and demand-based utilization of hydrogen-based fuel cell. The proposed system is attractive owing to its simplicity, ease of control and low cost. Also it can be easily adjusted to accommodate different and any number of energy sources. A complete description of this system is presented along with its simulation results which ascertain its feasibility.Index Terms -step-up dc-dc converter, maximum power point tracking, hybrid energy system, variable speed wind turbine, photovoltaic array, fuel cell, PWM voltage source inverter, PI controller.

Quantification of carbon flux distribution in the metabolic network of microalgae remains important to understand the complex interplay between energy metabolism, carbon fixation, and assimilation pathways. This is even more relevant with respect to cyclic metabolism of microalgae under light-dark cycle. In the present study, flux balance analysis (FBA) was carried out for an indigenous isolate Chlorella sp. FC2 IITG under photoautotrophic and heterotrophic growth conditions. A shift in intracellular flux distribution was predicted during transition from nutrient sufficient phase to nutrient starvation phase of growth. Further, dynamic flux analysis (dFBA) was carried out to capture light-dark metabolism over discretized pseudo steady state time intervals. Our key findings include the following: (i) unlike heterotrophic condition, oxidative pentose phosphate (PP) pathway, and Krebs cycle were relatively inactive under photoautotrophic growth; (ii) in both growth conditions, while transhydrogenation reaction was highly active, glyoxalate shunt was found to be nonoperative; (iii) flux distribution during transition period was marked with up regulation of carbon flux toward nongrowth associated (NGA) maintenance energy, oxidative phosphorylation, and photophosphorylation; (iv) redirection of carbon flux from polysaccharide and neutral lipid resulted in up regulation of Krebs cycle flux in the dark phase; (v) elevated glycolytic and acetyl-CoA flux were coupled with induction of neutral lipid during light cycle of the growth; (vi) significantly active photophosphorylation in the light phase was able to satisfy cellular energy requirement without need of oxidative PP pathway; and (vi) unlike static FBA, dFBA predicted an unaltered NGA maintenance energy of 1.5 mmol g(-1) DCW h(-1).

Effect of physical parameters such as initial pH, agitation (rpm), and temperature (°C) for cellulase production from Bacillus subtilis AS3 was investigated. Central composite design of experiments followed by multiple desirability function was applied for the optimization of cellulase activity and cell growth. The effect of the temperature and agitation was found to be significant among the three independent variables. The optimum levels of initial pH, temperature, and agitation for alkaline carboxymethylcellulase (CMCase) production predicted by the model were 7.2, 39°C, and 121 rpm, respectively. The CMCase activity with unoptimized physical parameters and previously optimized medium composition was 0.43 U/mL. The maximum activity (0.56 U/mL) and cell growth (2.01 mg/mL) predicted by the model were in consensus with values (0.57 U/mL, 2.1 mg/mL) obtained using optimized medium and optimal values of physical parameters. After optimization, 33% enhancement in CMCase activity (0.57 U/mL) was recorded. On scale-up of cellulase production process in bioreactor with all the optimized conditions, an activity of 0.75 U/mL was achieved. Consequently, the bacterial cellulase employed for bioethanol production expending (5%, w/v) NaOH-pretreated wild grass with Zymomonas mobilis yielded an utmost ethanol titre of 7.56 g/L and 11.65 g/L at shake flask and bioreactor level, respectively.

To understand the post-transcriptional molecular mechanisms attributing to oleaginousness in microalgae challenged with nitrogen starvation (N-starvation), the longitudinal proteome dynamics of Chlorella sp. FC2 IITG was investigated using multipronged quantitative proteomics and multiple reaction monitoring assays. Physiological data suggested a remarkably enhanced lipid accumulation with concomitant reduction in carbon flux towards carbohydrate, protein and chlorophyll biosynthesis. The proteomics-based investigations identified the down-regulation of enzymes involved in chlorophyll biosynthesis (porphobilinogen deaminase) and photosynthetic carbon fixation (sedoheptulose-1,7 bisphosphate and phosphoribulokinase). Profound up-regulation of hydroxyacyl-ACP dehydrogenase and enoyl-ACP reductase ascertained lipid accumulation. The carbon skeletons to be integrated into lipid precursors were regenerated by glycolysis, β-oxidation and TCA cycle. The enhanced expression of glycolysis and pentose phosphate pathway enzymes indicates heightened energy needs of FC2 cells for the sustenance of N-starvation. FC2 cells strategically reserved nitrogen by incorporating it into the TCA-cycle intermediates to form amino acids; particularly the enzymes involved in the biosynthesis of glutamate, aspartate and arginine were up-regulated. Regulation of arginine, superoxide dismutase, thioredoxin-peroxiredoxin, lipocalin, serine-hydroxymethyltransferase, cysteine synthase, and octanoyltransferase play a critical role in maintaining cellular homeostasis during N-starvation. These findings may provide a rationale for genetic engineering of microalgae, which may enable synchronized biomass and lipid synthesis.

The effect of different pretreatment methods, temperature, and enzyme concentration on ethanol production from 8 lignocellulosic agrowaste by simultaneous saccharification and fermentation (SSF) using recombinant cellulase and Saccharomyces cerevisiae were studied. Recombinant cellulase was isolated from E. coli BL21 cells transformed with CtLic26A-Cel5-CBM11 full-length gene from Clostridium thermocellum and produced in both batch and fed-batch processes. The maximum cell OD and specific activity in batch mode were 1.6 and 1.91 U/mg, respectively, whereas in the fed-batch mode, maximum cell OD and specific activity were 3.8 and 3.5 U/mg, respectively, displaying a 2-fold increase. Eight substrates, Syzygium cumini (jamun), Azadirachta indica (neem), Saracens indica (asoka), bambusa dendrocalmus (bamboo), Populas nigra (poplar), Achnatherum hymenoides (wild grass), Eucalyptus marginata (eucalyptus), and Mangifera indica (mango), were subjected to SSF. Of three pretreatments, acid, alkali, and steam explosion, acid pretreatment Syzygium cumini (Jamun) at 30°C gave maximum ethanol yield of 1.42 g/L.

The present study reports evaluation of an indigenous microalgal isolate Chlorella sp. FC2 IITG as a potential candidate for biodiesel production. Characterization of the strain was performed under photoautotrophic, heterotrophic, and mixotrophic cultivation conditions. Further, an open-pond cultivation of the strain under outdoor conditions was demonstrated to evaluate growth performance and lipid productivity under fluctuating environmental parameters and in the presence of potential contaminants. The key findings were: (1) the difference in cultivation conditions resulted in significant variation in the biomass productivity (73-114 mg l⁻¹ day⁻¹) and total lipid productivity (35.02-50.42 mg l⁻¹ day⁻¹) of the strain; (2) nitrate and phosphate starvation were found to be the triggers for lipid accumulation in the cell mass; (3) open-pond cultivation of the strain under outdoor conditions resulted in biomass productivity of 44 mg l⁻¹ day⁻¹ and total lipid productivity of 10.7 mg l⁻¹ day⁻¹; (4) a maximum detectable bacterial contamination of 7 % of the total number of cells was recorded in an open-pond system; and (5) fatty acid profiling revealed abundance of palmitic acid (C16:0), oleic acid (C18:1) and linoleic acid (C18:2), which are considered to be the key elements for suitable quality biodiesel.