Sunil Khanna

Biomethanation of banana peel and pineapple waste

Biomethanation of banana peel and pineapple wastes studied at various HRTs showed a higher rate of gas production at lower retention time. The lowest possible HRT for banana peel was 25 days, resulting in a maximum rate of gas production of 0.76 vol/vol/day with 36% substrate utilization, while pineapple-processing waste digesters could be operated at 10 days HRT, with a maximum rate of gas production of 0.93 vol/vol/day and 58% substrate utilization. For pineapple-processing waste lowering of retention time did not affect the methane content significantly; however, with banana peel an HRT below 25 days showed a drastic reduction in methane content.

A cellulase-poor, thermostable, alkalitolerant xylanase produced by Bacillus circulans AB 16 grown on rice straw and its application in biobleaching of eucalyptus pulp.

Abstract Bacillus circulans AB 16 isolated from a garbage dump produced appreciable quantities (19.28 IU/ml) of extracellular thermophilic xylanase, but negligible quantities of cellulase, when grown on 0.3% xylan. The optimum pH for the enzyme was 6.0–7.0, but it was stable over a wide range of pH (5.0–9.0). The optimum temperature was 80°C. The organism produced 20.6 IU/ml of xylanase in shake flask on rice straw, an inexpensive lignocellulosic biomass. Glucose, fructose, xylose and other sugars induced enzyme levels only in the range 0.82–2.52 IU/ml. The crude enzyme produced on rice straw showed good thermal and pH stability, retaining 67% activity after 1 h at 70°C, pH 9 and 84.5% activity after 2 h at 65°C, pH 9. The enzyme had a half-life of 24 h at 70°C, pH 7. When the xylanase from B. circulans AB 16 was used in the prebleaching of eucalyptus Kraft pulp the amount of chlorine was reduced by 20% without any decrease in brightness. The viscosity of xylanase-treated pulp was 9.5–9.7 cp, whereas that of the pulp treated exclusively with chlorine was 9.2 cp.

Biomethanation of rice and wheat straw

When rice or wheat straw was added to cattle dung slurry and digested anaerobically, daily gas production increased from 176 to 331 l/kg total solids with 100% rice straw and to 194 l/kg total solids with 40% wheat straw. Not only was methane production enhanced by adding chopped crop residues but a greater biodegradability of organic matter in the straws was achieved.

Enhanced production, purification and characterisation of a novel cellulase-poor thermostable, alkalitolerant xylanase from Bacillus circulans AB 16

Abstract A thermophilic Bacillus circulans AB 16, isolated from a garbage dump produced novel extracellular cellulase-poor, thermostable xylanase in basal medium containing rice straw. The xylanase yield was enhanced more than two and a half fold in the presence of tryptone and other media modifications. The highest xylanase activity obtained in liquid culture was 55 IU/ml. Two xylanases Xyl A and Xyl B were purified to homogenity by Q Sepharose and Sepharose 6B chromatograph. Xyl A ( M r 30 000) had a pH optima of 6 and a temperature optima of 75–80°C, while Xyl B ( M r 22 000) also had a pH optima of 6 but with a temperature optima of 65–70°C. Both Xyl A and Xyl B had a pH optima of 6 but retained 46% activity at pH 8. Xyl A retained 70% activity at 65°C, pH 9 and 2 h incubation while Xyl B retained 34% under the similar conditions. Both Xyl A and Xyl B showed 90% inhibition in activity by 1 mM Hg 2+ . The hydrolysis pattern of Xyl A yielded mainly xylobiose with lower amount of xylo-oligosaccharides and xylose while Xyl B yielded mainly higher oligosaccharides with lesser amounts of xylobiose and negligible amounts of xylose. The crude enzyme from B. circulans AB 16 showed higher chromophore release of 0.360 U as compared to Xyl A and Xyl B with a chromophore release of 0.115 and 0.069 units and thus would be more useful for pulp bleaching than purified xylanases.

Production of a thermostable alkali-tolerant xylanase from Bacillus circulans AB 16 grown on wheat straw

Bacillus circulans AB 16 was able to produce 50 IU/ml of xylanase, with negligible cellulase activity when grown on untreated wheat straw. The pH optimum of the crude enzyme was 6–7 with a temperature optimum of 80 ∘C. The enzyme showed high pH and thermal stability retaining 100% activity at 60 ∘C, pH 8 and 9 after 2.5 h of incubation. The residual activity at 70 ∘C after 2.5 h was 62% and 45% at pH 8 and 9, respectively. At 75 ∘C only 22.2% activity remained at pH 8 after 1 h incubation. Since Kraft pulp is alkaline this enzyme could be used for prebleaching of pulp at temperatures up to 70 ∘C without pH adjustment.

Enhanced biosurfactant production through cloning of three genes and role of esterase in biosurfactant release

BackgroundBiosurfactants have been reported to utilize a number of immiscible substrates and thereby facilitate the biodegradation of panoply of polyaromatic hydrocarbons. Olive oil is one such carbon source which has been explored by many researchers. However, studying the concomitant production of biosurfactant and esterase enzyme in the presence of olive oil in the Bacillus species and its recombinants is a relatively novel approach.ResultsBacillus species isolated from endosulfan sprayed cashew plantation soil was cultivated on a number of hydrophobic substrates. Olive oil was found to be the best inducer of biosurfactant activity. The protein associated with the release of the biosurfactant was found to be an esterase. There was a twofold increase in the biosurfactant and esterase activities after the successful cloning of the biosurfactant genes from Bacillus subtilis SK320 into E.coli. Multiple sequence alignment showed regions of similarity and conserved sequences between biosurfactant and esterase genes, further confirming the symbiotic correlation between the two. Biosurfactants produced by Bacillus subtilis SK320 and recombinant strains BioS a, BioS b, BioS c were found to be effective emulsifiers, reducing the surface tension of water from 72 dynes/cm to as low as 30.7 dynes/cm.ConclusionThe attributes of enhanced biosurfactant and esterase production by hyper-producing recombinant strains have many utilities from industrial viewpoint. This study for the first time has shown a possible association between biosurfactant production and esterase activity in any Bacillus species. Biosurfactant-esterase complex has been found to have powerful emulsification properties, which shows promising bioremediation, hydrocarbon biodegradation and pharmaceutical applications.

Biosurfactant Production and Potential Correlation with Esterase Activity

Biosurfactants (microbial surfactants) are surface active compounds produced extracellularly or as part of the cell membrane by several bacterial and fungal species. They have the unique property of reducing the surface and interfacial tension of liquids. Biosurfactants have applications in the field of agriculture, petroleum, microbial enhanced oil recovery, biomedical sciences, cosmetics, food processing and pharmaceuticals. The global biosurfactants market has grown gradually. Regardless of their greater biodegradability and reduced toxicity, cost competitiveness still remains the major concern for biosurfactant production. However, recombinant or metabolically engineered hyper producing strains combined with optimized cultivation conditions have made it possible for many companies to reap the benefits of ‘green’ biosurfactant technology. Simultaneously, biosurfactants and bioemulsifiers showing esterase activities and having potential applications are reported to form stable oil-water emulsions with hydrophobic substrates such as hexadecane and polyaromatic hydrocarbons. Biosurfactant production and release of esterases by the microbial cells is shown to be synchronized and symbiotically beneficial in some species. Several bacterial biosurfactant and esterase genes have been identified, cloned and expressed for their enhanced production. This review article emphasizes on the present worldwide scenario of biosurfactant production, correlation between biosurfactant production and esterase activity, recent developments in this line of research and future prospects.

Diversity of 16S rRNA and dioxygenase genes detected in coal-tar-contaminated site undergoing active bioremediation.

Aims:  In order to develop effective bioremediation strategies for polyaromatic hydrocarbons (PAHs) degradation, the composition and metabolic potential of microbial communities need to be better understood, especially in highly PAH contaminated sites in which little information on the cultivation‐independent communities is available.

Biodegradation of cellulosic and lignocellulosic waste by Pseudoxanthomonas sp R-28

A microbial consortium, designated Con R, was established by successive sub-cultivation which can degrade 83% of filter paper after 15 days of incubation over control. Among the 14 bacterial isolates obtained from Con R, only bacterial isolate (R-28) was capable of degrading filter paper. Based on 16S rRNA gene sequence, R-28 was identified as Pseudoxanthomonas sp R-28. After 5 days of incubation, degradation efficiencies of Pseudoxanthomonas sp R-28 on filter paper and pure cellulosic waste were 96% and 95% respectively as compared to control. Pseudoxanthomonas sp R-28 also degraded 60% of non-pretreated rice straw after 7 days as compared to control. The degradation kinetics through a modified logistic model showed high correlation coefficient (R(2)) of 0.965 and 0.665 for cellulosic and rice straw waste degradation respectively. Micro scale structural analysis showed the development of fissures and gaps over time which further supported the degradation potential of Pseudoxanthomonas sp R-28.

Pyrene Degradation by Bacillus pumilus Isolated from Crude Oil Contaminated Soil

Bacillus pumilus (MTCC 1002) isolated from crude oil contaminated soil and identified by 16S rDNA gene sequence analysis, was capable of growing in the presence of 50 μg/ml of pyrene. During growth on pyrene B. pumilus was able to co-metabolize 64% of 50μg/ml pyrene in basal medium containing 0.5% glucose in 35 days while in pulse-chase studies, as assessed by HPLC analysis, log phase. B. pumilus cells were able to uptake approximately 11% of 100 μg pyrene as pure substrate in 7 hours at 30°C. 9-methoxyphenanthrene and phthalate were identified as metabolic intermediates by GC-MS during degradation of pyrene by B. pumilus. This report implicates B. pumilus as a potential pyrene biodegrader suitable for practical field applications for effective in situ PAH bioremediation.