Kaustav Aikat

Study of bio-degradation and bio-decolourization of azo dye by Enterobacter sp. SXCR.

The objective of this study was to evaluate the decolourization potential of textile dyes by a relatively newly identified bacteria species, Enterobacter sp. SXCR which was isolated from the petroleum polluted soil samples. The bacterial strain was identified by 16S rRNA gene sequence analysis. The effects of operational conditions like initial dye concentration, pH, and temperature were optimized to develop an economically feasible decolourization process. The isolate was able to decolourize sulphonated azo dye (Congo red) over a wide range (0.1–1 gl−1), pH 5–9, and temperature 22–40°C in static condition. Anaerobic condition with minimal salt medium supplemented with 2 gl−1 glucose, pH 7 and 34°C were considered to be the optimum decolourizing condition. The bacterial isolate SXCR showed a strong ability to decolourize dye (0.2 gl−1) within 93 h. The biodegradation was monitored by UV–vis, fourier transform infra-red spectroscopy (FTIR) spectroscopy and high performance liquid chromatography (HPLC). Furthermore, the involvement of azoreductase in the decolourization process was identified in this strain. Cells of Enterobacter cloacae were immobilized by entrapment in calcium-alginate beads. Immobilized bacterial cells were able to reduced azo bonds enzymatically and used as a biocatalyst for decolourization of azo dye Congo red. Michaelis–Menten kinetics was used to describe the correlation between the decolourization rate and the dye concentration.

Aspergillus fumigatus NITDGPKA3 Provides for Increased Cellulase Production

A cellulolytic fungal strain, Aspergillus fumigatus NITDGPKA3, was isolated from straw retting ground. Cellulase and xylanase production by A. fumigatus NITDGPKA3 in submerged fermentation of rice straw was studied. The culture conditions for maximum enzyme production were found to be initial pH 4, 1% substrate concentration, temperature 30°C, incubation time 5 days, 0.2% tryptone as nitrogen source, and inoculum volumes 7% v/v (for cellulase) and 5% v/v (for xylanase). Addition of Tween 80 in fermentation broth improved xylanase production (193.58 IU/ml) much more compared to cellulase production (6.53 IU/ml). Xylanase activity found in the culture broth was approximately 50% higher compared to most of the reported data. The crude enzyme was further applied for reducing sugar production from alkali pretreated rice straw, where a dosage of 40 IU/g CMCase produced 0.522 g reducing sugar/g dry substrate after 36 hours which was higher than that in the reported literature. The high concentration of reducing sugar yield was most probably due to the extraordinarily high titer of β-glucosidase (80.1 IU/ml) found in the crude enzyme. The crude enzymes secreted by Aspergillus fumigatus NITDGPKA3 efficiently hydrolyzed alkali pretreated rice straw suggesting that Aspergillus fumigatus NITDGPKA3 is a robust microorganism.

Cellulase and Xylanase Production from Rice Straw by a Locally Isolated Fungus Aspergillus fumigatus NITDGPKA3 under Solid State Fermentation - Statistical Optimization by Response Surface Methodology

Alkali pretreated rice straw was used as substrate for cellulase production by a locally isolated fungus Aspergillus fumigatus NITDGPKA3 under solid state fermentation. Critical process parameters such as incubation period, temperature, basal medium content and pH were statistically optimized for an enhanced cellulase and xylanase yield by response surface methodology. The design predicted an optimum yield of 3.1 IU/g dry substrate, 64.18 IU/g dry substrate and 1040.57 IU/g dry substrate for FPase, CMCase and xylanase respectively under the optimum conditions of incubation period of 90 h, temperature at 33 o C, initial basal medium content of 62% and initial pH 4. The experimental values under optimum conditions correlated well with the predicted results. Further, crude enzyme extract from Aspergillus fumigatus NITDGPKA3 was used for saccharification of pretreated rice straw and this released 189.50 mg/g of reducing sugar. This work was carried out in the Department of Biotechnology, National Institute of Technology, Durgapur - 713209, West Bengal, India, during the period 2010 to 2011.

Kinetic Study of Acid Hydrolysis of Rice Straw

Rice straw is a renewable, cheap, and abundant waste in tropical countries. The pentose content of rice straw can be used as a substrate for many types of value-added products such as xylitol and biofuel. Dilute acid hydrolysis mainly releases pentose from rice straw. The objective of the study was to determine the effect of H2SO4 concentration and reaction time on the xylose production. The variation of the main product xylose with the reaction time was described by a kinetic model and kinetic parameters were calculated to describe the variation of the xylose production with time. The optimum yield (19.35 g/L) was obtained at 0.24 mol/L H2SO4 and 30 minutes.

Insights from the Molecular Dynamics Simulation of Cellobiohydrolase Cel6A Molecular Structural Model from Aspergillus fumigatus NITDGPKA3.

Global demand for bioethanol is increasing tremendously as it could help to replace the conventional fossil fuel and at the same time supporting the bioremediation of huge volume of cellulosic wastes generated from different sources. Ideal genetic engineering approaches are essential to improve the efficacy of the bioethanol production processes for real time applications. A locally isolated fungal strain Aspergillus fumigatus NITDGPKA3 was used in our laboratory for the hydrolysis of lignocellulose with good cellulolytic activity when compared with other contemporary fungal strains. An attempt is made to sequence the cellobiohydrolases (CBHs) of A. fumigatus NITDGPKA3, model its structure to predict its catalytic activity towards improving the protein by genetic engineering approaches. Herein, the structure of the sequenced Cellobiohydrolases (CBHs) of A. fumigatus NITDGPKA3, modelled by homology modelling and its validation is reported. Further the catalytic activity of the modelled CBH enzyme was assessed by molecular docking analysis. Phylogenetic analysis showed that CBH from A. fumigatus NITDGPKA3 belongs to the Glycohydro 6 (Cel6A) super family. Molecular modeling and molecular dynamics simulation suggest the structural and functional mechanism of the enzyme. The structures of both the cellulose binding (CBD) and catalytic domain (CD) have been compared with most widely studied CBH of Trichoderma reesei. The molecular docking with cellulose suggests that Gln 248, Pro 287, Val236, Asn284, and Ala288 are the main amino acids involved in the hydrolysis of the β, 1-4, glycosidic bonds of cellulose.