Characterization of Bacillus nealsonii strain KBH10 capable of reducing aqueous mercury in lab-scale reactor

The environmental release of Mercury is continuously increasing with high degree of mobility, transformation and amplified toxicity. Improving remediation strategies is becoming increasingly important to achieve more stringent environmental safety standards. This study develops a lab-scale reactor for bioremediation of aqueous mercury using a biofilm producing bacterial strain, KBH10 isolated from mercury polluted soil. The strain was found resistant to 80 mg/L of HgCl2 and identified as Bacillus nealsonii via 16S rRNA gene sequence analysis. The strain KBH10 was characterized for optimum growth parameters and its mercury biotransformation potential was validated through mercuric reductase assay. A packed-bed column bioreactor was designed for biofilm-mediated mercury removal from artificially contaminated water and residual mercury was estimated. Strain KBH10 could grow at a range of temperature (20–50 °C) and pH (6.0–9.0) with optimum temperature established at 30 °C and pH 7.0. The optimum mercuric reductase activity (77.8 ± 1.7 U/mg) was reported at 30 °C and was stable at a temperature range of 20–50 °C. The residual mercury analysis of artificially contaminated water indicated 60.6 ± 1.5% reduction in mercury content within 5 h of exposure. This regenerative process of biofilm-mediated mercury removal in a packed-bed column bioreactor can provide new insight of its potential use in mercury bioremediation.

Production and characterization of surfactin-like biosurfactant produced by novel strain Bacillus nealsonii S2MT and it's potential for oil contaminated soil remediation

Background Biosurfactants, being highly biodegradable, ecofriendly and multifunctional compounds have wide applications in various industrial sectors including environmental bioremediation. Surfactin a member of lipopeptide family which considered as one of the most powerful biosurfactant due to its environmental applications, emulsification activities as well as therapeutic properties. Therefore, the aim of this study to investigate the surfactin like biosurfactants produced by newly strain S2MT and their potential applications for soil remediation. Results In this study, a novel biosurfactant producing strain Bacillus nealsonii S2MT was investigated from the lake sediment that reduced the surface tension 34.15± 0.6 mN/m -1 with excellent emulsifying potential 55± 0.3% in kerosene oil. Additionally, the highest biosurfactant product 1300 mg/L -1 was achieved during which the composition of the culture medium was optimized through a response surface methodology (RSM). Results showed that 2% glycerol and 0.1% NH 4 NO 3 were the best carbon/nitrogen substrates for biosurfactant production. The most significant parameters such as temperature (30 °C), pH (8), agitation (100 rpm), NH 4 NO 3 (0.1%), yeast extract (0%) and NaCl (0.5%) contributed to the surface tension reduction and therefore enhancing the biosurfactant yield. Moreover, the obtained product was found to be highly stable at environmental factors such as salinity, pH and temperature variations. In addition, the biosurfactant product was chemically characterized as cyclic lipopeptide relating to surfactin-like isoforms (C 13 -C 15 ) with a thin-layer chromatography (TLC) and liquid chromatography and mass spectroscopy (LC/MS) respectively. The corresponding biosurfactant displayed 43.6± 0.08 and 46.7± 0.01% remediation of heavy engine-oil contaminated soil at 10 and 40 mg/L concentrations respectively. Conclusion This study, therefore, confirmed that the strain S2MT was not only a potential biosurfactant producer but also an efficient and environmentally acceptable candidate for soil remediation compared to synthetic compounds.