P. Kanmani

Remediation of chromium contaminants using bacteria

Chromium contaminants emanating from industrial activities pose a significant threat to human’s well-being. Chromium (III) and Chromium (VI) are the forms in which they are commonly encountered, of which the trivalent form is relatively benign. Hence, biological reduction of hexavalent chromium has been widely explored by researchers, yielding fruitful outcomes, opening up exciting avenues and also throwing up new challenges. This article attempts to review this area of research. Microbes, especially bacteria capable of Chromium (VI) reduction, belonging to a heterogeneous group have been isolated from contaminated sites. They exhibit plasmid-mediated chromate resistance and the reduction is enzymatically mediated. Reduction studies have been carried out with free and immobilized enzymes as well as whole cells. Experiments have been carried out in specifically designed bioreactors operated in batch and continuous modes. Although significant progress has been made, much needs to be done for its successful in situ application as the organism may not withstand the Chromium concentration or may be impeded by the presence of other toxicants. With molecular engineering, it may be possible to derive strains with improved performance even under stressful field conditions.

PRODUCTION OF POLYHYDROXYALKANOATES FROM RALSTONIA EUTROPHA USING PADDY STRAW AS CHEAP SUBSTRATE

Polyhydroxyalkanoates are polyesters of natural origin accumulated in form of intracellular granules by a wide variety of bacterial strains as candidates for biodegradable polymers, possessing material properties similar to the synthetic thermoplastics and elastomers. Paddy straw (lignocellulosic substrate) after hydrolysis was used as the carbon source for the production of polyhydroxyalkanoates from the predominant polyhydroxyalkanoates producer Ralstonia eutropha MTCC 1472. The effect of hydrolysed straw in the modified mineral salt media on bacterial growth and polyhydroxyalkanoates accumulation was analysed. Fourier transform infrared spectroscopy, thermogravimetric analysis and differential scanning calorimetry were performed on the extracted polyhydroxyalkanoates sample. At a dry cell weight of 19.2xa0g/L, 37.55xa0% polyhydroxyalkanoates accumulation was achieved; thus, paddy straw can be efficiently used as a cheap carbon source for industrial production of the polyhydroxyalkanoates.

Environmental applications of chitosan and cellulosic biopolymers: A comprehensive outlook

Biopolymers are substances naturally produced by living organisms and are hence considered to be eco-friendly and sustainable. Chitosan and cellulose are of specific significance owing to their abundant availability, ease of modification, and application potential. On the environmental front, their coagulating and flocculating effects have helped in wastewater clarification, while minimizing the dependability on synthetic polyelectrolytes. Biopolymer based hydrogels and nanocomposite films have functioned as effective biosorbents in removing an array of organic and inorganic pollutants, including xenobiotics, from wastewater. Specifically, they have been vastly harnessed for heavy metal and dye adsorption. They have also played a pivotal part in other environmental applications including anti-desertification, natural bio-sealants for preventing concrete leaks and proton conducting membranes in electrochemical devices. Such recent research on the environmental applications of biopolymers has been comprehensively analysed, thus providing a fresh insight into the future prospects of research in this domain.

An insight into microbial lipases and their environmental facet

Lipases are serine hydrolases that catalyze the hydrolysis and synthesis of esters formed from glycerol and long-chain fatty acids, by acting at the oil–water interface. Lipases from microbial sources have received heightened attention for an array of industrial applications, and these enzymes have been well exploited in the environmental sector as well. In this article, we present an overview of microbial lipase, including the microorganisms from which it could be produced; the application of recombinant DNA technology tools to produce lipase with enhanced properties, the effective use of waste materials as substrates for lipase production; the usage of statistical tools to efficiently optimize the production medium; lipase purification strategies; and the immobilization of the enzyme on a variety of support materials. The next section of the article provides a gist of its application in diversified spheres and focusses exclusively on the environmentally relevant ones. Lipase-catalyzed esterification, transesterification, and interesterification reactions, an emerging area of green chemistry; lipase-mediated in vitro biopolymer synthesis and degradation; and the application of lipase for remediating fat and oil constituents in wastewater are dealt with in-depth. When its full potential is harnessed, the enzyme could play a pivotal role in environmental management.

Enzymatic degradation of polyhydroxyalkanoate using lipase from Bacillus subtilis

Abstract Polyhydroxyalkanoates (PHAs) are an important class of biodegradable polymers synthesized by a few bacteria under nutrient-limiting conditions. In this study, the lipase-catalysed degradation of PHA synthesized by Enterobacter sp. was monitored. For this, the lipase-encoding gene from Bacillus subtilis DI2 was PCR-amplified, cloned into a T vector system and sequenced. It was expressed in Escherichia coli DH5α cells, the recombinant enzyme was purified 24.25-fold, and its molecular weight was determined to be around 28xa0kDa. When PHA biodegradation studies were carried out with this enzyme, gel permeation chromatography showed 21.3 and 28.3xa0% molecular weight decrease and weight loss, respectively. Further, scanning electron micrographs revealed alterations in polymer surface morphology. Changes in molecular vibrations were noticed in the FTIR spectra. When the chemical shifts in NMR spectra were studied, a steep reduction in area under the peak at 1.57xa0ppm was observed. In the heating range of 30–930xa0°C employed during thermogravimetry analysis, the degraded sample showed a total of 45.82xa0% weight loss, as against 18.89xa0% for the native sample. The melting temperature (Tm) of the polymer was also brought down from 126.22 to 118.18xa0°C, as inferred from differential scanning calorimetry. Lipase-catalysed chain scission reactions could thus be used to generate low molecular weight functional biopolymers with wide-ranging pharmaceutical applications, such as in sustained drug release.

Optimizing the nutrient feeding strategy for PHA production by a novel strain of Enterobacter sp.

AbstractnThe influence of nutrient limitation on polyhydroxyalkanoate (PHA) accumulation was studied using a novel PHA-producing strain of Enterobacter sp. The effect of N/C ratio on growth and accumulation of PHA was studied by varying the ratio from 0.02 to 0.1. Biomass concentration, dry cell weight, protein content and the amount of PHA accumulated were estimated for each N/C ratio. It was found that the increase in N/C ratio resulted in increase in culture concentration up to 3.25xa0g/l of dry cell weight. Polyhydroxyalkanoate concentration was found to be maximum at N/C ratio of 0.04 (67.8xa0µg/ml), and further increase in N/C ratio resulted in lesser amount of PHA. Analytical procedures such as FTIR and NMR were done to validate the obtained PHA biopolymer.

Pretreatment of coconut mill effluent using celite‐immobilized hydrolytic enzyme preparation from Staphylococcus pasteuri and its impact on anaerobic digestion

Biological treatment of oil and grease (O&G)‐containing industrial effluents has long been a challenging issue. Practically feasible avenues to bring down their O&G load and enhance treatability are desired. In one such endeavour, the partially purified lipase from Staphylococcus pasteuri COM‐4A was immobilized on celite carrier and applied for the enzymatic hydrolysis of unsterilized coconut oil mill effluent. In batch hydrolysis experiments, optimum conditions of 1% (w/v) immobilized lipase beads, one in four effluent dilution, and a contact time of 30 h resulted in 46% and 24% increase in volatile fatty acids and long‐chain fatty acids and a concomitant 52% and 32% decrease in O&G and chemical oxygen demand (COD) levels, respectively. Batch anaerobic biodegradation trials with this prehydrolyzed effluent showed 89%, 91%, and 90% decrease in COD, proteins, and reducing sugars, respectively. These results were validated in a hybrid stirred tank—upflow anaerobic sludge blanket reactor. Average COD and O&G reductions effected by the hybrid reactor were found to be 89% and 88%, whereas that by the control reactor without enzymatic hydrolysis were only 60% and 47%, respectively. A maximum of 0.86 L methane gas was generated by the hybrid reactor per gram of VS added. Hence, this celite‐immobilized crude lipase, sourced from a native laboratory isolate, seems to be a workable alternative to commercial enzyme preparations for the management of lipid‐rich industrial effluents.

Hydrolytic Enzyme Profiling of Bacillus Subtilis COM6B and Its Application in the Bioremediation of Groundnut Oil Mill Effluent

Industrial effluents rich in oil and grease pose hindrance to the functioning of wastewater treatment units and also affect the quality of receiving water bodies. Pretreatment of such wastewaters to bring about lipid hydrolysis makes them more amenable to conventional biological treatment and hydrolytic enzymes, especially lipases, find promising applications in this sector. In our study, the bacterial strain Bacillus subtilis COM6B isolated from groundnut mill effluent was cultivated in minimal media based on residual oil waste from the extraction process, in which it produced lipase and other extracellular hydrolytic enzymes such as protease and amylase. Applying response surface methodology led to a 1.8-fold increase in oil waste removal by the isolate. As a further study, the effluent discharged from the oil mill was treated in batch mode using pure cultures of the isolate and the effects of incubation time, inoculum size and effluent dilution on the treatment process were investigated. A maximum of 95, 93 and 98 % reduction in biochemical oxygen demand, chemical oxygen demand and oil and grease respectively, were achieved after treatment with COM6B. Hence, the isolate could serve as a potential candidate for remediating the fat and oil contaminants and reducing the organic load of wastewaters.

Gene cloning, expression, and characterization of the Bacillus amyloliquefaciens PS35 lipase

Abstract Lipases are enzymes of immense industrial relevance, and, therefore, are being intensely investigated. In an attempt to characterize lipases at molecular level from novel sources, a lipase gene from Bacillus amyloliquefaciens PS35 was cloned, heterologously expressed in Escherichia coli DH5α cells and sequenced. It showed up to 98% homology with other lipase sequences in the NCBI database. The recombinant enzyme was then purified from E. coli culture, resulting in a 19.41-fold purification with 9.7% yield. It displayed a preference for long-chain para-nitrophenyl esters, a characteristic that is typical of true lipases. Its optimum pH and temperature were determined to be 8.0 and 40 °C, respectively. The half-lives were 2.0, 1.0 and 0.5 h at 50 °C, 60 °C and 70 °C, respectively. The metal ions K+ and Fe3+ enhanced the enzyme activity. The enzyme displayed substantial residual activity in the presence of various tested chemical modifiers, and interestingly, the organic solvents, such as n-hexane and toluene, also favored the enzyme activity. Thus, this study involves characterization of B. amyloliquefaciens lipase at molecular level. The key outcomes are novelty of the bacterial source and purification of the enzyme with desirable properties for industrial applications.

Exopolysaccharide from Bacillus sp. YP03: its properties and application as a flocculating agent in wastewater treatment

Exopolysaccharides (EPS) are polymeric substances composed of sugars and are produced by microbes to form colonies and inhibit the growth of other organisms. In the present study, the bacterial strain Bacillus sp. YP03 was isolated from soil sample using a high-sucrose selective medium, the produced EPS recovered using ethanol precipitation, and lyophilized. In sugar analysis, it was found to be rich in fructose content, amounting to 86.1%, and further displayed appreciable antioxidant, emulsification, and flocculation activities. EPS concentration of 140xa0µg/ml, pH of 7.5, and the presence of trivalent metal cations augmented its flocculating ability. When applied as a coagulant aid in the treatment of municipal wastewater, up to 47 and 89% reductions of chemical oxygen demand and total suspended solids, respectively, were witnessed. Owing to these encouraging results, Bacillus sp. EPS could be applied as a potentially beneficial flocculant in wastewater treatment, for achieving accentuated TSS and organic load removal during primary sedimentation.