- Inhibitory Effect of Volatiles Emitted From Alcaligenes faecalis N1-4 on Aspergillus flavus and Aflatoxins in Storage. [Journal Article]
- FMFront Microbiol 2019; 10:1419
- Controlling aflatoxigenic Aspergillus flavus and aflatoxins (AFs) in grains and food during storage is a great challenge to humans worldwide. Alcaligenes faecalis N1-4 isolated from tea rhizosphere s…
Controlling aflatoxigenic Aspergillus flavus and aflatoxins (AFs) in grains and food during storage is a great challenge to humans worldwide. Alcaligenes faecalis N1-4 isolated from tea rhizosphere soil can produce abundant antifungal volatiles, and greatly inhibited the growth of A. flavus in un-contacted face-to-face dual culture testing. Gas chromatography tandem mass spectrometry revealed that dimethyl disulfide (DMDS) and methyl isovalerate (MI) were two abundant compounds in the volatile profiles of N1-4. DMDS was found to have the highest relative abundance (69.90%, to the total peak area) in N1-4, which prevented the conidia germination and mycelial growth of A. flavus at 50 and 100 μL/L, respectively. The effective concentration for MI against A. flavus is 200 μL/L. Additionally, Real-time quantitative PCR analysis proved that the expression of 12 important genes in aflatoxin biosynthesis pathway was reduced by these volatiles, and eight genes were down regulated by 4.39 to 32.25-folds compared to control treatment with significant differences. And the A. flavus infection and AFs contamination in groundnut, maize, rice and soybean of high water activity were completely inhibited by volatiles from N1-4 in storage. Scanning electron microscope further proved that A. flavus conidia inoculated on peanuts surface were severely damaged by volatiles from N1-4. Furthermore, strain N1-4 showed broad and antifungal activity to other six important plant pathogens including Fusarium graminearum, F. equiseti, Alternaria alternata, Botrytis cinerea, Aspergillus niger, and Colletotrichum graminicola. Thus, A. faecalis N1-4 and volatile DMDS and MI may have potential to be used as biocontrol agents to control A. flavus and AFs during storage.
- Metagenomic assembly provides a deep insight into the antibiotic resistome alteration induced by drinking water chlorination and its correlations with bacterial host changes. [Journal Article]
- JHJ Hazard Mater 2019 Jun 27; 379:120841
- Chlorination can contribute to the enrichment of specific antibiotic resistance genes (ARGs) in drinking water, but the underlying molecular ecological mechanisms remain unknown, which may hinder the…
Chlorination can contribute to the enrichment of specific antibiotic resistance genes (ARGs) in drinking water, but the underlying molecular ecological mechanisms remain unknown, which may hinder the assessment and control of the resulting health risks. In this study, metagenomic assembly and Resfams annotation were used to profile the co-occurrence patterns of ARGs, mobile genetic elements (MGEs) and their bacterial hosts, as well as the correlations of potential pathogens with the antibiotic resistome, in a full-scale drinking water treatment and transportation system. Seven ARG types involved in different resistance mechanisms occurred in drinking water and chlorination enhanced the total abundance of the ARGs (p < 0.05). The ARGs encoding resistance-nodulation-cell division and ATP-binding cassette antibiotic efflux pumps predominated in all the samples and were primarily responsible for the ARG accumulation. After chlorination, the ARGs were primarily carried by predominant Sphingomonas, Polaromonas, Hyphomicrobium, Acidovorax, Pseudomonas and Fluviicola. Further, enrichment of the bacterial hosts and MGEs greatly contributed to alteration of the antibiotic resistome. Pseudomonas alcaligenes, carrying multiple ARGs, was identified as a potential pathogen in the chlorinated drinking water. These findings provide novel insights into the host-ARG relationship and the mechanism underlying the resistome alteration during drinking water chlorination.
- Degradation mechanisms of sulfamethoxazole and its induction of bacterial community changes and antibiotic resistance genes in a microbial fuel cell. [Journal Article]
- BTBioresour Technol 2019 Jun 12; 289:121632
- In this study, more than 85.1% of sulfamethoxazole (SMX) could be degraded within 60 h. The strengthening of microbial metabolisms and the sustainment of electrical stimulation contributed to the rap…
In this study, more than 85.1% of sulfamethoxazole (SMX) could be degraded within 60 h. The strengthening of microbial metabolisms and the sustainment of electrical stimulation contributed to the rapid removal of SMX in microbial fuel cells (MFCs). High-performance liquid chromatography identified that SMX could be thoroughly degraded into less harmful alcohols and methane after the MFC processing. In addition, the major role of Shewanella sp. and Geobacteria sp. in power generation, and the promotion of Alcaligenes, Pseudomonas and Achromobacter in SMX degradation have been demonstrated. Moreover, this study further proved that the copy numbers of targeted antibiotic resistance genes and integrons produced in MFCs were much lower than those found in conventional wastewater treatment plants; MFCs seem to be a promising alternative to reduce antibiotics in wastewater treatment and water purification.
- Arsenite biotransformation by Rhodococcus sp.: Characterization, optimization using response surface methodology and mechanistic studies. [Journal Article]
- STSci Total Environ 2019 Jun 07; 687:577-589
- A large population of the world is under increased health risk due to consumption of arsenic contaminated groundwater. The present study investigates the arsenic resistance and arsenic biotransformin…
A large population of the world is under increased health risk due to consumption of arsenic contaminated groundwater. The present study investigates the arsenic resistance and arsenic biotransforming ability in three bacterial species, namely Bacillus arsenicus, Rhodococcus sp. and Alcaligenes faecalis for employing them in potential groundwater bioremediation programmes. The tolerance to pH levels for the 3 organisms are 6-9 for A. faecalis, 5-10 for Rhodococcus and 5-9 for B. arsenicus. The arsenic bio-oxidation capacity was qualitatively confirmed by using the silver nitrate method and all three bacteria were able to convert arsenite to arsenate. The arsenite tolerance capacity (MIC values) were found to be 3 mM, 7 mM and 12 mM for B. arsenicus, A. faecalis and Rhodococcus sp. respectively. The changes in cellular morphology of these strains under various arsenic stress conditions were studied using advanced cell imaging techniques such as scanning electron microscopy and Atomic Force Microscopy. Rhodococcus sp. emerged as a potential candidate for bioremediation application. A response surface methodology was employed to optimize key parameters affecting arsenic removal (pH, Iron (II) soluble, concentration of humic acid and initial arsenic concentration) and at optimized conditions, experimental runs demonstrated 48.34% removal of As (III) (initial concentration = 500 μg/L) in a duration of 6 h, with complete removal after 48 h. Evidences from this work indicate that arsenic removal occurs through bioaccumulation, biotransformation and biosorption. The present study makes the first attempt to investigate the arsenic removal capability of Rhodococcus sp. in synthetic groundwater by employing bacterial whole cell assays. This study also sheds light on the arsenic tolerance and detoxification mechanisms employed by these bacteria, knowledge of which could be crucial in the successful implementation of in-situ bioremediation programmes.
- Evaluation of cultivable aerobic bacterial flora from Russell's viper (Daboia russelii) oral cavity. [Journal Article]
- MPMicrob Pathog 2019 Jun 01; 134:103573
- Snake mouths contain a wide range of bacteria. Identifying these bacteria in snakes is very important to obtain an understanding of the etiological agents of secondary infections that may result from…
Snake mouths contain a wide range of bacteria. Identifying these bacteria in snakes is very important to obtain an understanding of the etiological agents of secondary infections that may result from accidents during handling and/or snake bites. The present study aims to determine the pattern of oral bacterial flora of nine healthy Russell's vipers (Daboia russelii), and their susceptibility to common antibiotics. A total of 94 isolates were obtained in pure form, which demonstrated noticeable colony characteristics and which were further studied with several biochemical tests. The strains that showed distinctive colonies, morphology and biochemical parameters were additionally subjected to phylogenetic characterization using 16S rRNA gene sequences. Furthermore, all these isolates were studied for antibiotic susceptibility. The oral cavity of the Russell's viper harbors a wide range of pathogenic bacteria, including Gram-negative genera: Proteus sp., Pseudomonas sp., Salmonella sp., Providencia sp., Alcaligenes sp., Morganella sp., as well as E. coli, and Gram-positive genera: Bacillus and Enterococcus sp., Staphylococcus sp. and Lysinobacillus sp. Most of the isolates were resistant to antibiotics viz. penicillin, Amoxyclav, oxacillin, methicillin and streptomycin while sensitive towards imipenem, amikacin, norfloxacin, gatifloxacin, ciprofloxacin, gentamicin, tetracycline, chloramphenicol and azithromycin. The present study documents diverse bacteria predominant in the oral cavity of Daboia russelii and studied their antibiotic susceptibilities.
- Identification and characterization of a novel pic gene cluster responsible for picolinic acid degradation in Alcaligenes faecalis JQ135. [Journal Article]
- JBJ Bacteriol 2019 Jun 03
- Picolinic acid (PA) is a natural toxic pyridine derivative. Microorganisms can degrade and utilize PA for growth. However, the full catabolic pathway of PA and its physiological and genetic foundatio…
Picolinic acid (PA) is a natural toxic pyridine derivative. Microorganisms can degrade and utilize PA for growth. However, the full catabolic pathway of PA and its physiological and genetic foundation remain unknown. In this study, we identified a gene cluster, designated picRCEDFB4B3B2B1A1A2A3, responsible for the degradation of PA from Alcaligenes faecalis JQ135. Our results suggest that PA degradation pathway occurs as follows: PA was initially 6-hydroxylated to 6-hydroxypicolinic acid (6HPA) by PicA (a PA dehydrogenase). 6HPA was then 3-hydroxylated by PicB, a four-component 6HPA monooxygenase, to form 3,6-dihydroxypicolinic acid (3,6DHPA), which was then converted into 2,5-dihydroxypyridine (2,5DHP) by the decarboxylase PicC. 2,5DHP was further degraded to fumaric acid, through PicD (2,5DHP 5,6-dioxygenase), PicE (N-formylmaleamic acid deformylase), PicF (maleamic acid amidohydrolase), and PicG (maleic acid isomerase). Homologous pic gene clusters with diverse organizations were found to be widely distributed in α-, β-, and γ-Proteobacteria. Our findings provide new insights into the microbial catabolism of environmental toxic pyridine derivatives.ImportancePicolinic acid is a common metabolite of L-tryptophan and some aromatic compounds and is an important intermediate in organic chemical synthesis. Although the microbial degradation/detoxification of picolinic acid has been studied for over 50 years, the underlying molecular mechanisms are still unknown. Here, we show that the pic gene cluster is responsible for the complete degradation of picolinic acid. The pic gene cluster was found to be widespread in other α-, β-, and γ-Proteobacteria. These findings provide a new perspective for understanding the catabolic mechanisms of picolinic acid in bacteria.
- Microbial degradation of organophosphorus pesticides: novel degraders, kinetics, functional genes, and genotoxicity assessment. [Journal Article]
- ESEnviron Sci Pollut Res Int 2019; 26(21):21668-21681
- Farmland soil sprayed with organophosphorus pesticides (OPs) annually was investigated for the identification and characterization of OP-degrading microorganisms. Six bacterial strains were identifie…
Farmland soil sprayed with organophosphorus pesticides (OPs) annually was investigated for the identification and characterization of OP-degrading microorganisms. Six bacterial strains were identified, including Brevundimonas faecalis MA-B12 and Alcaligenes faecalis subsp. parafaecalis MA-B13 for methamidophos degradation, Citrobacter freundii TF-B21 and Ochrobactrum intermedium TF-B23 for trichlorfon degradation, Ochrobactrum intermedium DV-B31 for dichlorvos degradation, and Bacillus cereus for dimethoate degradation. The optimal biodegradation conditions for OPs were obtained at pH 7.0 and incubation temperature ranging from 28 to 37 °C. In an 8-day batch test, biodegradation of the four OPs all followed first-order kinetics, with biodegradation rates ranging from 58.08 to 96.42%. Functional genes responsible for OPs degradation were obtained, including ophB, ampA, opdE, opd, opdA, and mpd. As these strains were indigenous strains isolated from farmland soils, they can be potentially used as bacterial consortium for the bioremediation of mixed OP-contaminated soils. A time-course genotoxicity assessment of the degradation products was done by a bacterial whole-cell bioreporter, revealing that biodegradation of trichlorfon, dichlorvos, and dimethoate resulted a decreased genotoxicity within 5 days, which, however, significantly increased on day 8. The result demonstrated that more toxic products may be produced during the biodegradation processes of OPs, and more attention should be put not only on the pesticides themselves, but also on the toxic effects of their degradation products. To the best of our knowledge, this is for the first time that the genotoxicity of OP degradation products was evaluated by the bioreporter assay, broadening our understanding on the genotoxic risks of OPs during biodegradation process. Graphical Abstract.
- Altering N2O emissions by manipulating wheat root bacterial community. [Journal Article]
- SRSci Rep 2019 May 20; 9(1):7613
- Nitrous oxide (N2O) is a greenhouse gas and a potent ozone-depleting substance in the stratosphere. Agricultural soils are one of the main global sources of N2O emissions, particularly from cereal fi…
Nitrous oxide (N2O) is a greenhouse gas and a potent ozone-depleting substance in the stratosphere. Agricultural soils are one of the main global sources of N2O emissions, particularly from cereal fields due to their high areal coverage. The aim of this study was to isolate N2O-reducing bacteria able to mitigate N2O emissions from the soil after inoculation. We isolated several bacteria from wheat roots that were capable of N2O reduction in vitro and studied their genetic potential and activity under different environmental conditions. Three of these isolates- all carrying the nitrous oxide reductase-encoding clade I nosZ, able to reduce N2O in vitro, and efficient colonizers of wheat roots- presented different N2O-reduction strategies when growing in the root zone, possibly due to the different conditions in situ and their metabolic preferences. Each isolate seemed to prefer to operate at different altered oxygen levels. Isolate AU243 (related to Agrobacterium/Rhizobium) could reduce both nitrate and N2O and operated better at lower oxygen levels. Isolate AU14 (related to Alcaligenes faecalis), lacking nitrate reductases, operated better under less anoxic conditions. Isolate NT128 (related to Pseudomonas stutzeri) caused slightly increased N2O emissions under both anoxic and ambient conditions. These results therefore emphasize the importance of a deep understanding of soil-plant-microbe interactions when environmental application is being considered.
- Degradation of azo dyes by Alcaligenes aquatilis 3c and its potential use in the wastewater treatment. [Journal Article]
- AEAMB Express 2019 May 17; 9(1):64
- In the present study, Alcaligenes aquatilis was found to decolorize 82% Synazol red 6HBN after incubation of 4 days at 37 °C and pH 7. Maximum decolorization was found under static conditions by usin…
In the present study, Alcaligenes aquatilis was found to decolorize 82% Synazol red 6HBN after incubation of 4 days at 37 °C and pH 7. Maximum decolorization was found under static conditions by using saw dust and yeast extract as carbon and nitrogen source. It also showed promising potential to decolorize mixture of multiple dyes at a rate of more than 86% in 5 days. Decolorization of dye had positive influence on the growth of bacterium as growth rate was increased along with decolorization. The cleavage of azo bond was confirmed through TLC, HPLC and GC-MS analysis. The dye metabolites produced during bacterial treatment are linked to various pathways including ATP synthesis process. The absence of peaks of wavelength 1612/cm and 1532/cm in bacterially treated FTIR sample demonstrated the cleavage of azo bond. Microbial growth in decolorized dye wastewater shows that bacterially decolorized wastewater is unharmful for the growth of micro-flora. The high decolorization ability of A. aquatilis 3c to convert toxic azo dyes into useful end products may find potential applications in the environmental biotechnology.
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- [Treatment of Piggery Biogas Slurry by Enhanced Biological Contact Oxidation with HN-AD Bacteria]. [Journal Article]
- HJHuan Jing Ke Xue 2019 May 08; 40(5):2349-2356
- The conventional pretreatment process for swine wastewater is anaerobic fermentation. This process leads to the formation of high ammonia nitrogen, low carbon, and piggery biogas slurry, which usuall…
The conventional pretreatment process for swine wastewater is anaerobic fermentation. This process leads to the formation of high ammonia nitrogen, low carbon, and piggery biogas slurry, which usually results in poor denitrification effect, complicated process flow, and long startup period for the subsequent treatment process. In this study, a novel biological enhanced Biological Contact Oxidation (BCO) process using HN-AD bacteria as microbial inoculants, and PAN activated carbon fiber filler as biofilm carrier was proposed for the treatment of piggery biogas slurry. In the early stage of sludge acclimation, it was found that when NH4+-N concentration was higher than 500 mg·L-1, the nitrification and COD removal in BCO was severely inhibited. When the BCO was enhanced by HN-AD bacteria, however, the tolerance concentration of NH4+-N for bacteria in BCO could reach 600 mg·L-1 and the removal efficiency of NH4+-N, COD, and TN could still remain at a high level. The bio-enhanced BCO process was used to treat the piggery biogas slurry. The average removal rates of NH4+-N, TN, and COD were 86.9%, 70.5%, and 74.4%, respectively, which were higher than the 57.6%, 50.3%, and 50.0% of the traditional treatment process. The concentration of the pollutants mentioned above in the effluent was below the relevant discharge standards. The changes in the microbial community structure during the enrichment process of functional bacteria were studied by high-throughput sequencing technique. The results showed that the dominant bacteria belonging to HN-AD in the biofilm during the sludge acclimation process was Alcaligenes. After the addition of the HN-AD agent, however, the dominant bacteria were Diaphorobacter, Acinetobacter, and Thauer, and the relative abundance of Acinetobacter was much higher than that in the microbial inoculants. The results of scanning electron microscopy further confirmed the existence of bio-enhancement. The surface of the biofilm layer tightly attached to the filler was enriched with rod-like and globular HN-AD functional bacteria.