Rajendra Kumar Saxena

Microbial production of 1,3-propanediol: Recent developments and emerging opportunities

1,3-Propanediol, a valuable bifunctional molecule, can be produced from renewable resources using microorganisms. It has several promising properties for many synthetic reactions, particularly for polymer and cosmetic industries. By virtue of being a natural product, relevant biochemical pathways can be harnessed into fermentation processes to produce 1,3-propanediol. Various strategies for the microbial production of 1,3-propanediol are reviewed and compared in this article with their promises and constraints. Furthermore, genetic and metabolic engineering could significantly improve product yields and overcome the limitations of fermentation technology. Present review gives an overview on 1,3-propanediol production by wild and recombinant strains. It also attempts to encompass the various issues concerned in utilization of crude glycerol for 1,3-propanediol production, with particular emphasis laid on biodiesel industries. This review also summarizes the present state of strategies studied for the downstream processing and purification of biologically produced 1,3-propanediol. The future prospect of 1,3-propanediol and its potential as a major bulk chemical are discussed under the light of the current research.

Purification strategies for microbial lipases

Microbial lipases today occupy a place of prominence among biocatalysts owing to their ability to catalyze a wide variety of reactions in aqueous and non-aqueous media. The chemo-, regio- and enantio-specific behaviour of these enzymes has caused tremendous interest among scientists and industrialists. Lipases from a large number of bacterial, fungal and a few plant and animal sources have been purified to homogeneity. This has enabled their successful sequence determination and their three-dimensional structure leading to a better understanding of their unique structure-function relationships during various hydrolytic and synthetic reactions. This article presents a critical review of different strategies which have been employed for the purification of bacterial, yeast and fungal lipases. Since protein purification is normally done in a series of sequential steps involving a combination of different techniques, the effect of sequence of steps and the number of times each step is used is analyzed. This will prove to be of immense help while planning lipase purification. Novel purification technologies now available in this field are also reviewed.

A rapid plate assay for screening L-asparaginase producing micro-organisms

A pH and dye‐based fast procedure for screening l‐asparaginase‐producing micro‐organisms is reported. The procedure is suitable for bacterial and fungal screening. The results are obtained within 24 and 48 h for bacteria and fungi, respectively. The results correlate with quantitative estimations in culture broths.

Zn2+ biosorption by Oscillatoria anguistissima

Abstract Oscillatoria anguistissima showed a very high capacity for Zn 2+ biosorption (641 mg g −1 dry biomass at a residual concentration of 129·2 ppm) from solution and was comparable to the commmercial ion-exchange resin IRA-400C. Zn 2+ biosorption was rapid, pH dependent and temperature independent phenomenon. Zn 2+ adsorption followed both Langmuir and Freundlich models. The specific uptake (mg g −1 dry biomass) of metal decreased with increase in biomass concentration. Pretreatment of biomass did not significantly affect the biosorption capacity of O. anguistissima. The biosorption of zinc by O . anguistissima was an ion-exchange phenomenon as a large concentration of magnesium ions were released during zinc adsorption. The zinc bound to the biomass could be effectively stripped using EDTA (10 mM) and the biomass was effectively used for multiple sorption–desorption cycles with in-between charging of the biomass with tap water washings. The native biomass could also efficiently remove zinc from effluents obtained from Indian mining industries.

A comparative study of solvent-assisted pretreatment of biodiesel derived crude glycerol on growth and 1,3-propanediol production from Citrobacter freundii.

The rapidly growing biodiesel industry has created a scenario, where it is both important and challenging to deal with the enormous amount of crude glycerol generated as an inherent by-product. With every 100 gallons of biodiesel produced, 5-10 gallons of the crude glycerol is left behind containing several impurities which makes its disposal difficult. The objective of the present investigation was to evaluate the impact of biodiesel-derived crude glycerol upon microbial growth and production of 1,3-propanediol by Citrobacter freundii. Five different grades of crude glycerol (obtained from biodiesel preparation using jatropha, soybean, sunflower, rice bran and linseed oils) were used. Crude glycerol caused significant inhibition of microbial growth and subsequently 1,3-propanediol production as compared to pure glycerol. Therefore, a process was developed for the treatment of crude glycerol using solvents before fermentation wherein four different non-polar solvents were examined yielding different grades of pretreated glycerol. Subsequently, the potential toxic effects of pretreated glycerol on the growth and 1,3-propanediol production by C. freundii was evaluated. In case of petroleum ether-treated crude glycerol obtained from jatropha & linseed and hexane-treated crude glycerol obtained from rice bran, the yields obtained were comparable to the pure glycerol. Similarly, soybean-derived glycerol gave comparable results after treatment with either hexane or petroleum ether.

Parametric optimization and biochemical regulation of extracellular tannase from Aspergillus japonicus

Abstract Aspergillus japonicus produces maximum extracellular tannase activity after 24 h incubation. The enzyme is produced constitutively on simple and complex sugar substrates but activity is doubled in the presence of tannic acid as sole carbon source. Parametric optimization of the enzyme yielded 1·13-fold increase in enzyme production (33·06 U/ml) at 30°C and pH 6·6 with 0·2% glucose and 2% tannic acid in Czapek-Doxs minimal medium. The enzyme shows strong end-product repression with gallic acid.

Purification and characterization of a regiospecific lipase from Aspergillus terreus

Aspergillus terreus lipase was purified to homogeneity with 18.0% yield. The specific activity of the enzyme increased from 20.80 to 250 U/mg of protein. Ion exchange on Q‐Sepharose was highly effective in the purification process. The molecular mass of the purified enzyme was 41±1 kDa as determined by SDS/PAGE. The purified lipase showed excellent temperature tolerance (15–90 °C) and was highly thermostable, retaining 100% activity at 60 °C for 24 h. It showed good pH tolerance (3.0–12.0) and was stable over a pH range of 4.0–10.0 for 24 h. The activity of the enzyme was inhibited by ionic detergents, whereas non‐ionic detergents stimulated enzyme activity. Mg2+ and Ca2+ ions stimulated lipase activity, whereas Co2+, Cu2+, Ni2+ and Fe3+ ions caused inhibition. The enzyme was unaffected by the metal chelator EDTA or by 2‐mercaptoethanol and potassium ferrocyanide. At a concentration of 100 μM, 3,4‐dichloroisocoumarin caused weak inhibition with 40% loss of activity, but diethyl p‐nitrophenyl phosphate at the same concentration strongly inhibited enzyme activity (98.12% loss of activity), confirming that the A. terreus lipase is a serine hydrolase. The lipase was highly active on pig fat (151% relative activity) and groundnut oil (103% relative activity) and least active on kusum oil (18% relative activity). Extensive dialysis did not affect enzyme activity up to 168 h, suggesting the absence of any dialysable cofactor in the enzyme. The A. terreus lipase retained significant activity on freeze‐drying and had a shelf‐life of more than 6 months at room temperature. The A. terreus lipase exhibited 1,3‐regiospecificity and was stable in various organic solvents.

Decolorization of triphenylmethane dyes by the bird's nest fungus Cyathus bulleri

Decolorization of three triphenylmethane dyes by three birds nest fungi—Cyathus bulleri, C. stercoreus, and C. striatus—was studied. Cyathus bulleri was found to be the most efficient in decolorization as demonstrated by the disappearance of the dyes from cultures, monitored by decreases in absorbance. Growth of the Cyathus spp. was not affected by the presence of dyes in the cultures. Decolorization of dyes was also observed with extracellular culture filtrates, indicating exocellular activity. Laccase activity, tested in replicate cultures, was found to be maximum during the decolorization period. Nitrogen in the medium had no effect on decolorization.

Parametric optimisation of Aspergillus terreus lipase production and its potential in ester synthesis

Abstract Parametric optimisation of lipase from Aspergillus terreus yielded 7780 U/l in a medium containing corn oil (2% v/v) and casein (0.1% w/v). Maximum production was observed at pH 9.0 and at 37°C in 96 h. Secretion of lipase was increased by Ca2+ and Mg2+ ions. The enzyme has good potential for synthesis of fatty acid esters of sugars, sugar alcohols, aliphatic alcohols and ascorbic acid which are industrially important.

News & Notes: Sorption and Desorption of Cobalt by Oscillatoria anguistissima

Abstract.Oscillatoria anguistissima rapidly adsorbs appreciable amounts of cobalt from the aqueous solutions within 15 min of initial contact with the metal solution. O. anguistissima showed a high sequestration of cobalt at low equilibrium concentrations, and it followed the Freundlich model of adsorption. The adsorption is a strongly pH-dependent and temperature-independent phenomenon. The presence of Mg2+ and Ca2+ (100–200 ppm) resulted in decline in Co2+ adsorption capacity of Oscillatoria biomass. Sulphate and nitrate (0.75–10 mM) drastically reduced the extent of Co2+ biosorption. The biosorption of cobalt is an ion-exchange process as the Co2+ binding was accompanied by release of a large amounts of Mg2+ ions. Na2CO3 (1.0 mM) resulted in about 76% desorption of Co2+ from the loaded biomass.