Reduction of hexavalent chromium by Bacillus sp. isolated from chromite mine soils and characterization of reduced product

BACKGROUND: The reduction of highly mobile and toxic hexavalent chromium by bacterial strains is considered to be a viable alternative to reduce Cr(VI) contamination, in soils and water bodies, emanating from the overburden dumps of chromite ores and mine drainage. The present study reports the isolation of Cr(VI) resistant bacterial strains from an Indian chromite mine soil and their potential use in reduction of hexavalent chromium. RESULTS: Among the isolates, a bacterial strain (CSB‐4) was identified as Bacillus sp. based on standard biochemical tests and partial 16SrRNA gene sequencing, which was tolerant to as high as 2000 mg L^?1 Cr(VI) concentration. The strain was capable of reducing Cr(VI) to Cr(III) in different growth media. Under the optimized conditions pH ～7.0, 100 mg L^?1 Cr(VI), 35 °C temperature and stirring speed 100 rpm, CSB‐4 reduced more than 90% of Cr(VI) in 144 h. The time course reduction data fitted well an exponential rate equation yielding rate constants in the range 3.22 × 10^?2 to 6.5 × 10^?3 h^?1 for Cr(VI) concentration of 10–500 mg L^?1. The activation energy derived from temperature dependence rate constants between 25 and 35 °C was found to be 99 kJ mol^?1. The characterization of reduced product associated with bacterial cells by SEM‐EDS, FT‐IR and XRD was also reported. CONCLUSION: Reasonably high tolerance and reduction ability of indigenous Bacillus sp. (CSB‐4) for Cr(VI) under a wide range of experimental conditions show promise for its possible use in reclamation of chromite ore mine areas including soils and water bodies. Copyright © 2010 Society of Chemical Industry     

Evaluation of nutritional and nutraceutical potentials of three wild edible mushrooms from Similipal Biosphere Reserve,Odisha, India

A variety of edible mushrooms are growing in Similipal Biosphere Reserve (SBR), some of which are used as ethno-medicine by indigenous tribals. In the present study, three wild edible mushrooms viz., Russula vesca, Russula delica and Termitomyces eurrhizus of SBR were analyzed for their nutritional and mineral contents along with antioxidant and antibacterial potential. The results showed that these three mushrooms are rich sources of nutrients (protein, carbohydrate, starch, reducing sugars and low fats), micronutrients (vitamins and carotenoids) and minerals (P, K, Mn, Co, Ni, Cd, Fe) with promising bioactive properties (antioxidant and antibacterial potentials). In general, these mushrooms revealed high amounts of proteins (22.82–35.17 g/100 g) and carbohydrates (45.68–63.27 g/100 g) and low contents in fats (2.03–4.62 g/100 g), while micronutrients (vitamins and carotenoids) and minerals were present in significant amounts. The antioxidant potentials of three different solvent extracts (ethanol, methanol and aqueous) of studied wild mushrooms showed strong antioxidant properties (ABTS, DPPH, H₂O₂ and metal chelating activities) with scavenging potential up to 89 % at concentration 100 μg/ml. Total phenol content was found between 21.92–41.99 mg catechol/g extract and flavonoid 2.53–7.52 mg quercetin/g extract. The studied mushrooms possess moderate antibacterial properties with zones of inhibition ranging from 13 to 30 mm against six human pathogenic bacteria which are comparable with Amphoxyllin standard. Being a source of nutrients and molecules with medicinal potential, the studied mushrooms can be used in human diet as nutraceuticals/functional foods for maintaining and promoting health, longevity and life quality.     

Bioethanol production from tuber crops using fermentation technology: a review

Bioethanol, an alcohol produced by fermentation of plant biomass containing starch and sugars by micro-organisms, considered as a dominant form of fuel for future. Production of this renewable fuel, especially from starchy materials such as tuber crops, holds a remarkable potential to meet the future energy demand because of its high production and comparitively less demand for use as food and fodder. This review focuses on the world bioethanol production scenario from various tuber crops, namely cassava, sweet potato, potato, yam, aroids, sugar beet, etc., fermentation techniques and micro-organisms used in fermentation process along with its future prospects. The advances in metabolic pathway engineering and genetic engineering techniques have led to the development of micro-organisms capable of efficiently converting biomass sugars into ethanol. Several biotechnological tools that are also available for the improvement of microorganisms to meet the harsh environments typically met with certain industrial fermentation process are also discussed.     

Influence of reactors,microbial carbohydrate uptake,and metabolic pathways on ethanol production from grass biomass: A review

Grasses are considered to be potential lignocellulosic feedstock for renewable and sustainable biofuels such as bioethanol. However, the process involved, ie, pretreatment, enzymatic saccharification, and fermentation in conversion of these lignocellulosic biomass to bioethanol, remains expensive and at present is not affordable for industrial production. Thus, the present review assesses the influence of the recent technologies that can be employed for the bio‐refinery based pretreatment and enzymatic hydrolysis of grass biomass using advanced bioreactors. Since plant extracts have been seen to enhance the glucose uptake, an experiment was implemented to elucidate the role of plant extracts (bark extracts of Xylocarpus granatum) on glucose uptake capacity of microorganisms like Saccharomyces cerevisiae, Pichia sp., and Zymomonas mobilis and their subsequent ethanol production capability from glucose and xylose sugars. The results of these experiments indicated that supplementation of plant extracts promoted both glucose and xylose uptake in S. cerevisiae and Pichia sp. as compared with the control and Z. mobilis strain. Further, as Pichia sp. exhibited good uptake ability for both glucose and xylose, a model was proposed focusing on the gene silencing and operon concept in Pichia sp. for preferential pentose utilization during the fermentation of grass biomass to bioethanol.     

Environmental Quality of the Boula-Nuasahi Chromite Mine Area in India

Chromite mining can create hostile conditions for organisms in the surrounding environment. Overburden soil and mine water samples were collected and analyzed for their microbial diversity, nutrient content, and water quality at the Boula-Nuasahi Mine. Most of the water parameters that were measured exceed national/international standards. The microbial population was low (soil: 45 ± 0.06 × 10⁵ bacteria, 20 ± 0.03 × 10⁵ fungus) and the overburden soils have a low nutrient (N, P, K) content. The metal ions were found to have leached to nearby agriculture lands, making them less fertile for crop production. Overburden dumps and seepage water were found to be the main sources of chromium pollution.     

A novel fixed-grid interface-tracking algorithm for rapid solidification of supercooled liquid metal

Abstract

In this study, we present a novel fixed-grid interface-tracking method using finite volume method to simulate multidimensional rapid solidification (RS) of under-cooled pure metal. The discretized advection equation for solid fraction function is solved using the THINC/WLIC method, which is a VOF method. The governing equations for fluid flow are solved numerically using pressure-velocity coupling SIMPLE algorithm in a 2-D model with incompressible Newtonian fluid. The energy equation is modeled using an enthalpy-based formulation. The nonequilibrium solidification kinetics, interface tracking, undercooling, nucleation, heat transfer, and movement of liquid are included in the presented RS model.