Optimization of spore laccase production by Bacillus amyloliquefaciens isolated from wastewater and its potential in green biodecolorization of synthetic textile dyes.

The spore laccase enzyme production by B. amyloliquefaciens was optimized. It was characterized and tested for its textile dye decolorization potential. LB medium was found to be the most promising growth medium with addition of glucose (1-2%), yeast extract (0.1%), FeCl3 (0.01 mM) and MnCl2 (0.001 mM). The optimum spore laccase production was at pH 8, 30 °C, 1:5 medium to air ratio, 2% inoculum size and 7 days incubation. The characterization study of the enzyme showed the maximum activity at 60 °C and pH 6-7.5. It was induced by Ca+2, Mg+2, Fe+3, Zn+2, Cu+2 and Na+ at 1 mM concentration. Also, it was stable in the presence of methanol, ethanol, acetone and chloroform. In addition, it enhanced about 34% by 5 mM H2O2 and it was nearly stable at 10-20 mM H2O2. Furthermore, mediators such as ABTS, syrengaldazine and 2, 6 dimethyl phenol enhanced the spore laccase activity. The spore laccase enzyme efficiently decolorized direct red 81 and acid black 24 after 24 h. Phytotoxicity of the direct red 81 solution after decolorization by tested spore laccase was lower than that of the untreated dye solution. Finally, this study added a promising spore laccase candidate for ecofriendly and cost-effective dye wastewater bio-decolorization.

Short-Term Biodegradation of Crude Petroleum Oil in Water by Photostimulated Janibacter terrae Strain S1N1.

Biodegradation is a sustainable green strategy that gives the opportunity for remediation of water contaminated with petroleum products. In this study, 12 bacterial isolates were recovered from River Nile, Egypt and screened for their potential to degrade a mixture of paraffinic petroleum crude oil. The most promising isolate was identified according to 16S rRNA sequencing as Janibacter terrae strain S1N1 (GenBank accession No. KX570955.1). In order to boost the biodegradation efficiency, the bacterial suspension was photostimulated by exposure to different irradiation doses using a low-power helium-neon (He-Ne) laser (λ = 632.8 nm). Maximum biodegradation was achieved after 4 min of exposure (134.07 J cm-2) at optimized pH value (6) and temperature (35 °C). The gas chromatography-mass spectrometry (GC-MS) analysis revealed the biodegradation of 96.5% of the substrate after only 48 h of incubation. The n-C17/Pr and n-C18/Ph ratios indicated a preferential biodegradation of iso-paraffines over normal ones. Meanwhile, pristane/phytane (Pr/Ph) ratios were indicative of selective biodegradation for pristane. The carbon preference index (CPI) was nearly around unity indicating the ability of Janibacter terrae to attack the odd and even n-alkanes simultaneously. These results support the superiority of irradiated bacteria in optimizing the biodegradation efficiency and shortening the time of treatment, thus proposing an eco-friendly technique in water bioremediation programs.

Applying Quantitative Microbial Risk Assessment Model in Developing Appropriate Standards for Irrigation Water.

This study aimed to apply a quantitative microbial risk assessment (QMRA) model to estimate the annual risk probability of Salmonella infection associated with the consumption of crops, which were irrigated with raw wastewater abstracted by farmers without official permission. Data generated from the model were used to propose realistic standards for Salmonella in irrigation water needed for safe crop production. Results demonstrated the presence of total coliforms, fecal coliforms, fecal streptococci, and Salmonella in wastewater samples. Salmonella was recorded on lettuce and spinach in 3 different harvesting events, although it was not found in data obtained for parsley plant. The QMRA scenario included surface irrigation, consumption of raw crops, and 1-day withholding period before harvest. The annual risk probability of Salmonella infection for consumers exceeded the target tolerable risk (7.7 × 10-4 ) for investigated crops. The Pearson's correlation coefficient between different annual risk probabilities showed significant correlation (p < 0.05). The levels of risk posed from spinach and lettuce were roughly similar, although they tended to be higher for lettuce. The optimum concentrations of Salmonella in irrigation water needed to satisfy the World Health Organization guidelines of disease burden (disability-adjusted life years 10-6 ) per person per year ranged from 34 to 119 via multiple-tube fermentation technique/100 mL, for spinach and lettuce plants, respectively. The study concluded that unofficial reuse of wastewater in irrigation is a principle route for crop contamination. Water quality monitoring programs should be integrated with QMRA investigations for better estimation of risk level. The fit parameters used could be tailored to cover a wide array of local situations in different countries. Models applied for viruses, helminths, and bacteria other than Salmonella are encouraged in future studies. Integr Environ Assess Manag 2020;16:353-361. © 2019 SETAC.