Optimization of Cr(VI) bioremediation in contaminated soil using indigenous bacteria

Bench-scale soil column experiments were carried out to evaluate the effectiveness of Cr（VI） bioremediation process in soils by using indigenous bacteria with the addition of bacteria nutrient media. Effects of particle size, spray intensity, initial Cr（VI） concentration, circulation mode and soil depth on Cr（VI） remediation were studied. Results show that soils after 6 d remediation with spray intensity controlled in the range of 29.6-59.2 mL/min could well fulfill the requirement of concrete aggregate and roadbed material usage, for the leaching toxicity concentration of the Cr（VI） in treated soils under the chosen condition is far less than 5 mg/L The leaching toxicity and fractions of both hexavalent chromium and trivalent chromium from remediated soils were determined and compared with that of untreated soil. The results show that water soluble Cr（VI） declines from 1520.54 mg/kg to 0.68 mg/kg, exchangeable Cr（VI） decreases from 34.83 mg/kg to 0.01 mg/kg and carbonates-bonded Cr（V1） falls from 13.55 mg/kg to 0.68 mg/kg. Meanwhile, a corresponding increase in carbonate-bonded Cr（III）, Fe and Mn oxides-bonded Cr（III） and organic matter-bonded Cr（III） are found. It reveals that indigenous bacteria can leach out water soluble Cr（VI）, exchangeable Cr（VI） and carbonates-bonded Cr（VI） from contaminated soil followed by converting into carbonate-bonded Cr（III）, Fe and Mn oxides-bonded Cr（IlI）, organic matter-bonded Cr（III） and residual Cr（III）.

Inactivation, reactivation and regrowth of indigenous bacteria in reclaimed water after chlorine disinfection of a municipal wastewater treatment plant

Disinfection of reclaimed water prior to reuse is important to prevent the transmission of pathogens. Chlorine is a widely utilized disinfectant and as such is a leading contender for disinfection of reclaimed water. To understand the risks of chlorination resulting from the potential selection of pathogenic bacteria, the inactivation, reactivation and regrowth rates of indigenous bacteria were investigated in reclaimed water after chlorine disinfection. Inactivation of total coliforms, Enterococcus and Salmonella showed linear correlations, with constants of 0.1384, 0.1624 and 0.057 L/（mg·min） and R 2 of 0.7617, 0.8316 and 0.845, respectively. However, inactivation of total viable cells by measurement of metabolic activity typically showed a linear correlation at lower chlorine dose （0-22 （mg·min）/L）, and a trailing region with chlorine dose increasing from 22 to 69 （mg·min）/L. Reactivation and regrowth of bacteria were most likely to occur after exposure to lower chlorine doses, and extents of reactivation decreased gradually with increasing chlorine dose. In contrast to total coliforms and Enterococcus, Salmonella had a high level of regrowth and reactivation, and still had 2% regrowth even after chlorination of 69 （mg·min）/L and 24 hr storage. The bacterial compositions were also significantly altered by chlorination and storage of reclaimed water, and the ratio of Salmonella was significantly increased from 0.001% to 0.045% after chlorination of 69 （mg·min）/L and 24 hr storage. These trends indicated that chlorination contributes to the selection of chlorine-resistant pathogenic bacteria, and regrowth of pathogenic bacteria after chlorination in reclaimed water with a long retention time could threaten public health security during wastewater reuse.

Relative Effectiveness of Ultraviolet Light Irradiation and Chlorination against Indigenous Bacteriophage and Bacteria in Primary Treated Wastewater

The effectiveness of chlorine and ultraviolet light at inactivating indigenous microbes in primary treated wastewater was examined in this study. The inactivation rates for somatic colipahge and F-specific bacteriophage were less than 2.5 log and 1 log, respectively, at either free chlorine doses of 6, 15 mg/L and 30 mg/L after 30 minutes contact time. However, E. coli and total coliforms were susceptible to chlorination and inactivated more than 4 log within first 15 minutes of contact time at any chlorine dosage tested. In contrast, the inactivation of bacteriophage was increased when increasing UV fluence. At the same disinfection effectiveness against E. coli, UV disinfection was more effective than chlorination against F-specific bacteriophages.

Antimicrobial Profile of Lactic Acid Bacteria Isolated from Vegetables and Indigenous Fermented Foods of India against Clinical Pathogens Using Microdilution Method

In dairy and food industries lactic acid bacteria （LAB） have been used in form of starter culture that plays vital role in fermentation; as flavouring and texturizing or as preservative agents. There is increasing evidence that lactobacilli which inhabit the gastrointestinal tract develop antimicrobial activities and participate in the host＇s defence system[1]. During fermentation, most of the LAB produces a number of different compounds like organic acids, hydrogen peroxide, diacetyl, acetaldehyde, carbon dioxide, polysaccharides, and proteinaceous compounds called bacteriocins or bacteriocinogenic peptides.

Field-based evidence for the enrichment of intrinsic antibiotic resistome stimulated by plant-derived fertilizer in agricultural soil

Animal manures have been demonstrated to enhance antibiotic resistance in agricultural soils.However,little is known about the effects of plant-derived fertilizer on soil antibiotic resistome.Herein,metagenomic sequencing was used to investigate the effects of a plantderived fertilizer processed from sugarcane and beet on soil antibiotic resistance genes(ARGs)in a soybean field along crop growth stages.ARG profiles in the soils amended by plant-derived fertilizer were compared with those in the soils amended by chicken manure.The abundance and diversity of total ARGs in the soils amended by plant-derived fertilizer were significantly(P<0.05)elevated at the sprout stage,to a level comparable to that in the manured soils.Whereas,unlike chicken manure mainly introducing manure-borne ARGs to soil,the plant-derived fertilizer was indicated to mainly enrich multidrug resistance genes in soil by nourishing indigenous bacteria.ARGs with abundances in amended soils significantly(P<0.05)higher than in unamended soils at the sprout stage of soybean were considered as enriched ARGs.Decrease in the abundance of the enriched ARGs was observed in both the amended soils from the sprout to the harvest.Network analysis further identified Proteobacteria and Bacteroidetes as the primary bacterial taxa involved in the temporal variation of the enriched ARGs in the soils amended by plant-derived fertilizer,while in manured soils were Firmicutes and Actinobacteria.As revealed by multivariate statistical analyses,variation of the enriched ARGs in the soils amended by plant-derived fertilizer was majorly attributed to the response of co-occurred bacteria to depleting nutrients,which was different from the failed establishment of manure-borne bacteria in the manured soils.Our study provided field-based evidence that plant-derived fertilizer stimulated the intrinsic antibiotic resistome,and proposed attention to the un-perceived risk since some clinically relevant ARGs originate and evolve from natural resistome.

Microbial reduction and migration of As/Fe mediated by electron shuttle:Differences between incorporated and adsorbed As(V)

Metal-reducing bacteria play a central and important role in the biogeochemical cycle of arsenic(As)and iron(Fe).Research on As/Fe migration from arsenic-containing iron minerals mediated by electronic shuttles is of significance to groundwater protection and human health.Further,the redox activity and bioavailability of goethite with differing occurrence and distribution of arsenic have not been studied clearly.In this study,the function of electron shuttle AQDS in Fe(III)bioreduction was determined.It was found that acidic conditions were conducive to the growth and reproduction of strain D2201,which was beneficial to the reduction of As(V)/Fe(III).The OD600nm value of the bacteria at pH 6 exceeded twice that at pH 8.Then,three types of goethite,namely pure goethite(Gt),coprecipitated As(V)-goethite(Gt-As),and adsorbed arsenic-goethite(Gt*As),were compared for microbial reduction reactivity.X-ray photoelectron spectroscopy analysis illustrated the proportion of OH-content in Gt-As was much lower than that of Gt and Gt*As,indicating Gt-As carried more surface defects and had higher bioavailability.The Fe(II)content released from AQDS-mediated bioreduction of Gt-As was two-fold higher than that of Gt and Gt*As at pH 7.In addition,pH significantly affected goethite bioreduction efficiency and arsenic migration degree.The dissolved Fe(II)concentration for Gt-As was 0.98,0.133,and 0.139 mM at pH 6,7,and 8,respectively;corresponding to dissolved As(T)content of 3.51,1.48,and 1.31μM within 9 days of culture.This study highlights the significant influence of AQDS and mineral structure on the As/Fe biochemical cycle,which will help further develop the bioremediation of arsenic-contaminated sediments.