Suresh Kumar Dubey

Biodegradation of trichloroethylene (TCE) by methanotrophic community

Laboratory incubation experiments were carried out to assess the potential of methanotrophic culture for degrading TCE. Measurements of the growth rate and TCE degradation showed that the methanotrophs not only grew in presence of TCE but also degraded TCE. The rate of TCE degradation was found to be 0.19 ppm h(-1). The reverse transcriptase-PCR test was conducted to quantify expression of pmoA and mmoX genes. RT-PCR revealed expression of pmoA gene only. This observation provides evidence that the pmoA gene was functionally active for pMMO enzyme during the study. The diversity of the methanotrophs involved in TCE degradation was assessed by PCR amplification, cloning, restriction fragment length polymorphism and phylogenetic analysis of pmoA genes. Results suggested the occurrence of nine different phylotypes belonging to Type II methanotrophs in the enriched cultures. Out of the nine, five clustered with, genera Methylocystis and rest got clustered in to a separate group.

Characterization of Listeria monocytogenes isolated from Ganges water, human clinical and milk samples at Varanasi, India

Listeria monocytogenes isolated from Ganges water, human clinical and milk samples were characterized by antibiotic susceptibility, serotype identification, detection of virulence genes and ERIC- and REP-PCR fingerprint analyses. All isolates were uniformly resistant to ampicillin, except two isolates, and showed variable resistance to gentamicin, cotrimoxazole, ofloxacin, rifampicin and tetracycline. Of the 20 isolates found positive for pathogens, seven (four human and three water isolates) belong to serogroups 4b, 4d and 4e; six (one human and five water isolates) belong to serogroups 1/2c and 3c; four milk isolates belong to serogroups 1/2b and 3b; and three milk isolates belong to serogroups 1/2a and 3a. Two water isolates, all human isolates, except one (Pb1) lacking inlJ gene, and three milk isolates possess inlA, inlC, plcA, prfA, actA, hlyA and iap genes. The remaining water and milk isolates showed variable presence of inlJ, plcA, prfA, and iap genes. ERIC- and REP-PCR based analyses collectively indicated that isolates of human clinical samples belong to identical or similar clone and isolates of water and milk samples belong to different clones. Overall study demonstrates the prevalence of pathogenic L. monocytogenes species in the environmental and clinical samples. Most of the isolates were resistant to commonly used antibiotics.

Biodegradation of chlorpyrifos by Pseudomonas sp. in a continuous packed bed bioreactor.

Biodegradation of chlorpyrifos (CP) by Pseudomonas (Iso 1) sp. was investigated in batch as well as continuous bioreactors packed with polyurethane foam pieces. The optimum process parameters for the maximum removal of CP, determined through batch experiments, were found to be: inoculum level, 300×10(6)CfumL(-1); CP concentration, 500mgL(-1); pH 7.5; temperature, 37°C and DO, 5.5mgL(-1). The continuous packed bed bioreactor was operated at various flow rates (10-40mLh(-1)) under the optimum conditions. The steady state CP removal efficiency of more than 91% was observed up to the inlet load of 300mgL(-1)d(-1). The bioreactor was sensitive to flow fluctuations but was able to recover its performance quickly and exhibited the normal plug-flow behavior. Accumulation of TCP (3,5,6-trichloro-2-pyridinol) affected the reactor performance.

Spatio-temporal variation and effect of urea fertilization on methanotrophs in a tropical dryland rice field.

Abstract Population size of methanotrophs in a dryland field planted to Oryza sativa L. variety Narendra-118 was quantified over a period of 13 weeks. Methanotroph numbers were higher in control plots (52.9–736.6×10 5 cells g −1 dry soil) than in plots treated with urea (43.8–676.0×10 5 cells g −1 dry soil), and were highest in the rhizosphere soil (499.8–736.6×10 5 cells g −1 dry soil) followed by bulk (451.4–684.1×10 5 cells g −1 dry soil) and bare (43.8–67.5×10 5 cells g −1 dry soil) soil. The concentrations of NH 4 + -N were significantly ( P −1 soil) than in bulk (4.1–8.3 μg g −1 soil) and bare soils (5.1–10.7 μg g −1 soil). The study suggests that the development of the rice rhizosphere brings about a spatial pattern in the distribution of methanotrophic bacteria which increases in size, over time, within the rhizosphere and adjoining bulk soil, and that the rhizosphere is a potential microsite of intense CH 4 oxidation activity.

Kinetics of bio-filtration of trichloroethylene by methanotrophs in presence of methanol.

The biodegradation of TCE was studied in a laboratory scale biofilter packed with wood charcoal and inoculated with mixed culture of methanotrophs isolated from local soil. The removal efficiency was found to be higher than 90% up to an inlet load of 5.1g/m(3)h. The maximum elimination capacity was 6.7g/m(3)h at an inlet loading rate of 11.3g/m(3)h. The reaction constants EC(max,)K(s) and K(i) calculated from the experimental results are also presented. The biodegradation process is found to be inhibited at higher TCE concentration. The carbon dioxide production rate has been found to be a linear function of elimination capacity. The DNA finger printing techniques has indicated the presence of functionally active methanotrophic community including Methylocystis sp. in the biofilter.

Virulence and genotypic characterization of Listeria monocytogenes isolated from vegetable and soil samples

BackgroundListeria monocytogenes, a foodborne pathogen is ubiquitous to different environments including the agroecosystem. The organism poses serious public health problem. Therefore, an attempt has been made to gain further insight to their antibiotic susceptibility, serotypes and the virulence genes.ResultsOut of the 10 vegetables selected, 6 (brinjal, cauliflower, dolichos-bean, tomato, chappan-kaddu and chilli), 20 isolates (10%) tested positive for L. monocytogenes. The prevalence of the pathogen in the respective rhizosphere soil samples was 5%. Noticeably, L. monocytogenes was absent from only cabbage, broccoli, palak and cowpea, and also the respective rhizospheric soils. The 30 isolates + ve for pathogenicity, belonged to serogroup 4b, 4d or 4e, and all were positive for inlA, inlC, inlJ, plcA, prfA, actA, hlyA and iap gene except one (VC3) among the vegetable isolates that lacked the plcA gene. ERIC- and REP-PCR collectively revealed that isolates from vegetables and their respective rhizospheric soils had distinct PCR fingerprints.ConclusionsThe study demonstrates the prevalence of pathogenic L. monocytogenes in the selected agricultural farm samples. The increase in the number of strains resistant to ciprofloxacin and/or cefoxitin seems to pose serious public health consequences.

Degradation kinetics of chlorpyrifos and 3,5,6-trichloro-2-pyridinol (TCP) by fungal communities.

Fungal isolates obtained from soil were used for degrading chlorpyrifos (CP) and TCP. The percentage degradation ranged from 69.4 to 89.8 for CP and 62.2 to 92.6 for TCP after one week. The values of K(s) and V(max) were different for different isolates. The K(s) ranged from 66.66 to 169.5mg/L and V(max) from 6.56 to 40.4 mg/L/d for CP and from 53.19 to 163.9 mg/L and 3.41 to 40.40 mg/L/d, respectively, for TCP. Fungal community showed high affinity for both CP and TCP. The genetic relatedness of isolate F1 to Aspergillus sp., F2 and F3 to Penicillium sp., F4 to Eurotium sp. and F5 to Emericella sp. were confirmed. The degradation potential was in the order: F1>F2=F3>F4>F5.

Current trends in trichloroethylene biodegradation: a review

Abstract Over the past few years biodegradation of trichloroethylene (TCE) using different microorganisms has been investigated by several researchers. In this review article, an attempt has been made to present a critical summary of the recent results related to two major processes - reductive dechlorination and aerobic co-metabolism used for TCE biodegradation. It has been shown that mainly Clostridium sp. DC-1, KYT-1, Dehalobacter, Dehalococcoides, Desulfuromonas, Desulfitobacterium, Propionibacterium sp. HK-1, and Sulfurospirillum bacterial communities are responsible for the reductive dechlorination of TCE. Efficacy of bacterial communities like Nitrosomonas, Pseudomonas, Rhodococcus, and Xanthobacter sp. etc. for TCE biodegradation under aerobic conditions has also been examined. Mixed cultures of diazotrophs and methanotrophs have been used for TCE degradation in batch and continuous cultures (biofilter) under aerobic conditions. In addition, some fungi (Trametes versicolor, Phanerochaete chrysosporium ME-446) and Actinomycetes have also been used for aerobic biodegradation of TCE. The available information on kinetics of biofiltration of TCE and its degradation end-products such as CO2 are discussed along with the available results on the diversity of bacterial community obtained using molecular biological approaches. It has emerged that there is a need to use metabolic engineering and molecular biological tools more intensively to improve the robustness of TCE degrading microbial species and assess their diversity.

Spatio-kinetic variation of methane oxidizing bacteria in paddy soil at mid-tillering: effect of N-fertilizers

Laboratory experiments were conducted to evaluate the variation ofpopulation size of methanotrophs (MOB) and CH4 oxidation pattern inflooded rice soils sampled at three spatial points (rhizosphere, bulk and baresoils). Rhizosphere soil had higher MOB population size (301.1 ×105 cells g−1 dry soil) than bulk(37.2× 105 cells g−1 dry soil) andbare soil (19.1 × 105 cells g−1dry soil). The population size of MOB followed a decreasing trend with respectto fertilizer (urea ≤ NH4NO3 ≤ NH4Cl≤ control). The result indicated that rhizosphere soil presented thestrongestCH4 oxidation activities, as shown by the highest values of the twokinetic parameters (Km(app) andVmax). Km andVmax increased significantly from bare to bulkto rhizosphere soil in control and fertilized soil and ranged from 6.2 to 133.2μg g−1 dry soil and from 0.03 to 0.41μg h−1 g−1 dry soil,respectively. The differences in Km andVmax among the three soils (rhizosphere, bulkand bare) in this study could be due to differential species composition ofmethanotrophic community and/or to conditioning of MOB under different soilmicroenvironments. The present study has demonstrated a competitive inhibition effectof NH4+-N on CH4 oxidation.

Bio-filtration of trichloroethylene using diazotrophic bacterial community

Biodegradation of TCE was studied in a biofilter packed with wood charcoal and inoculated with diazotrophic bacterial community isolated from local soil. Steady state TCE removal efficiencies higher than 85% were observed up to inlet load of 2.866 g m(-3) h(-1). The maximum elimination capacity of 5.31 g m(-3) h(-1) was observed at an inlet load of more than 7.90 g m(-3) h(-1). The biofilter was sensitive to fluctuations in the process conditions but could easily recover its performance after 10 days shutdown. Almost constant and small pressure drop per unit length and very negligible compaction was observed during the whole experimental period. The molecular analyses such as RT-PCR and gene sequencing revealed the presence of functionally active Azospirillum species in the biofilm.