A toxaphene-degrading bacterium related to Enterobacter cloacae, strain D1 isolated from aged contaminated soil in Nicaragua

Evidence for cometabolic transformation of weathered toxaphene under aerobic conditions using camphor as a co-substrate

AIMS

Toxaphene is a persistent organic pollutant, composed of approximately 1000 highly chlorinated bicyclic terpenes. The purpose of this study was to evaluate if camphor, a structural analogue of toxaphene, could stimulate aerobic biotransformation of weathered toxaphene.

METHODS AND RESULTS

Two enrichment cultures that degrade camphor as the sole carbon source were established from contaminated soil and biosolids. These cultures were used to evaluate aerobic transformation of weathered toxaphene. Only the biosolids culture could transform compounds of technical toxaphene (CTTs) in the presence of camphor, while no transformation was observed in the presence of glucose or with toxaphene as a sole carbon source. The transformed toxaphene had lower concentration of CTTs with longer retention times, and higher concentration of compounds with lower retention times. Gas chromatography with electron capture negative ion mass spectrometry (GC/ECNI-MS) showed that aerobic biotransformation mainly occurred with Cl₈ - and Cl₉ -CTTs compounds. The patterns of Cl₆ - and Cl₇ -CTTs were also simplified albeit to a much lesser extent. Seven camphor-degrading bacteria were isolated from the enrichment culture but none of them could degrade toxaphene.

CONCLUSION

Camphor degrading culture can aerobically transform CCTs via reductive pathway probably by co-metabolism using camphor as a co-substrate.

SIGNIFICANCE AND IMPACT OF THE STUDY

Since camphor is naturally produced by different plants, this study suggests that stimulation of aerobic transformation of toxaphene may occur in nature. Moreover plants, which produce camphor or similar compounds, might be used in bioremediation of contaminated soils.

Application of an Endophyte Enterobacter sp. TMX13 to Reduce Thiamethoxam Residues and Stress in Chinese Cabbage (Brassica chinensis L)

A strain of thiamethoxam-degrading endophyte, named TMX13, was isolated from roots of mulberry (Morus alba L.) and was identified as Enterobacter sp. Inoculating Chinese cabbage (Brassica chinensis L) with strain TMX13-gfp (gfp-labeled TMX13) could significantly reduce thiamethoxam residues in the aboveground part (edible portion) of the vegetable. The theoretical daily intake (TDI) of thiamethoxam via consumption of TMX13-gfp inoculated Chinese cabbage was 0.17 μg/kg body weight per day, far less than the prescribed acceptable daily intake (ADI) for this pesticide. TMX13-gfp colonization could increase the leaf chlorophyll content and plant biomass and promote the development of plant roots. Compared with the uninoculated treatment, the contents of malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) and the activity of superoxide dismutase (SOD) in leaves of the TMX13-gfp inoculated plants decreased by 18.4%-60.2%, suggesting that TMX13-gfp colonization could alleviate the oxidative stress induced by thiamethoxam exposure. The total amounts of organic acids and amino acids in root exudates from the TMX13-gfp inoculated Chinese cabbage decreased by 9.2% and 85.2%, respectively. Results of this study lead to the conclusion that the isolated endophyte Enterobacter sp. TMX13 could reduce thiamethoxam residues in edible vegetables, promote plant growth, and alleviate the phytotoxic effects induced by thiamethoxam exposure.

Ribonucleoside Diphosphate Reductase Plays an Important Role in Patulin Degradation by Enterobacter cloacae subsp. dissolvens

Patulin contamination is a worldwide concern due to its significant impact on human health. Several yeast strains have been screened for patulin biodegradation; however, little information is available on bacterial strains and their mechanism of degradation. In the present study, we isolated a bacterial strain TT-09 and identified it as Enterobacter cloacae subsp. dissolvens based on the BioLog system and 16S rDNA phylogenetic analysis. The strain was demonstrated to be able to transform patulin into E-ascladiol. Isobaric tags for relative and absolute quantitation and reverse transcription quantitative polymerase chain reaction analyses provided evidence that ribonucleoside diphosphate reductase (NrdA), an important enzyme involved in DNA biosynthesis, plays a crucial role in patulin degradation. Deletion of nrdA resulted in a total loss in the ability to degrade patulin in TT-09. These results indicate a new function for NrdA in mycotoxin biodegradation. The present study provides evidence for understanding a new mechanism of patulin degradation and information that can be used to develop new approaches for managing patulin contamination.

Biodegradation of malathion, α- and β-endosulfan by bacterial strains isolated from agricultural soil in Veracruz, Mexico

The objective of this study was to evaluate the capacity of two bacterial strains isolated, cultivated, and purified from agricultural soils of Veracruz, Mexico, for biodegradation and mineralisation of malathion (diethyl 2-(dimethoxyphosphorothioyl) succinate) and α- and β-endosulfan (6,7,8,9,10,10-hexachloro-1,5,5a,6,9,9a-hexahydro-6-9-methano-2,4,3-benzodioxathiepine-3-oxide). The isolated bacterial strains were identified using biochemical and morphological characterization and the analysis of their 16S rDNA gene, as Enterobacter cloacae strain PMM16 (E1) and E. amnigenus strain XGL214 (M1). The E1 strain was able to degrade endosulfan, whereas the M1 strain was capable of degrading both pesticides. The E1 strain degraded 71.32% of α-endosulfan and 100% of β-endosulfan within 24 days. The absence of metabolites, such as endosulfan sulfate, endosulfan lactone, or endosulfan diol, would suggest degradation of endosulfan isomers through non-oxidative pathways. Malathion was completely eliminated by the M1 strain. The major metabolite was butanedioic acid. There was a time-dependent increase in bacterial biomass, typical of bacterial growth, correlated with the decrease in pesticide concentration. The CO₂ production also increased significantly with the addition of pesticides to the bacterial growth media, demonstrating that, under aerobic conditions, the bacteria utilized endosulfan and malathion as a carbon source. Here, two bacterial strains are shown to metabolize two toxic pesticides into non-toxic intermediates.

Molecular perspectives and recent advances in microbial remediation of persistent organic pollutants

Nutrition and pollution stress stimulate genetic adaptation in microorganisms and assist in evolution of diverse metabolic pathways for their survival on several complex organic compounds. Persistent organic pollutants (POPs) are highly lipophilic in nature and cause adverse effects to the environment and human health by biomagnification through the food chain. Diverse microorganisms, harboring numerous plasmids and catabolic genes, acclimatize to these environmentally unfavorable conditions by gene duplication, mutational drift, hypermutation, and recombination. Genetic aspects of some major POP catabolic genes such as biphenyl dioxygenase (bph), DDT 2,3-dioxygenase, and angular dioxygenase assist in degradation of biphenyl, organochlorine pesticides, and dioxins/furans, respectively. Microbial metagenome constitutes the largest genetic reservoir with miscellaneous enzymatic activities implicated in degradation. To tap the metabolic potential of microorganisms, recent techniques like sequence and function-based screening and substrate-induced gene expression are proficient in tracing out novel catabolic genes from the entire metagenome for utilization in enhanced biodegradation. The major endeavor of today's scientific world is to characterize the exact genetic mechanisms of microbes for bioremediation of these toxic compounds by excavating into the uncultured plethora. This review entails the effect of POPs on the environment and involvement of microbial catabolic genes for their removal with the advanced techniques of bioremediation.

Anaerobic biotransformation of high concentrations of chloroform by an enrichment culture and two bacterial isolates

A fermentative enrichment culture (designated DHM-1) was developed that is capable of cometabolically biotransforming high concentrations of chloroform (CF) to nontoxic end products. Two Pantoea spp. were isolated from DHM-1 that also possess this dechlorination capability. Following acclimation to increasing levels of CF, corn syrup-grown DHM-1 was able to transform over 500 mg/liter CF in the presence of vitamin B(12) (approximately 3% of CF on a molar basis) at a rate as high as 22 mg/liter/day in a mineral salts medium. CO, CO(2), and organic acids were the predominant biodegradation products, suggesting that hydrolytic reactions predominate during CF transformation. DHM-1 was capable of growing on corn syrup in the presence of high concentrations of CF (as may be present near contaminant source zones in groundwater), which makes it a promising culture for bioaugmentation. Strains DHM-1B and DHM-1T transform CF at rates similar to that of the DHM-1 enrichment culture. The ability of these strains to grow in the presence of high concentrations of CF appears to be related to alteration of membrane fluidity or homeoviscous and homeophasic adaptation.

Biodegradation of tebuconazole by bacteria isolated from contaminated soils

The objective of this work was to isolate bacteria from soil historically exposed to tebuconazole and to evaluate the biodegradation of this fungicide by them. Tebuconazole is a commonly used systemic fungicide of the triazol group, which inhibits the sterol C-14 alpha-demethylation of 24-methylenedihydrolanosterol, a precursor of ergosterol, a cell membrane component in fungi. Microorganisms were isolated by different methods of soil sampling and the screening of degrading bacteria was performed in bioreactors cultivations, with some isolates showing the ability to degrade up to 42.76 mg L(- 1) of tebuconazole (51% of the initial concentration). These strains were identified by standard biochemical procedures as being Enterobacter sakazakii and Serratia sp. These bacteria present some important characteristics for potential uses on environmental bioremediation, considering that tebucanozale is an extremely recalcitrant chemical.

Biodegradability and toxicity assessment of trans-chlordane photochemical treatment

The removal of trans-chlordane (C(10)H(6)Cl(8)) from aqueous solutions was studied using UV, UV/H(2)O(2), UV/H(2)O(2)/Fe(2+), UV/TiO(2), or UV/TiO(2)/H(2)O(2) treatment using either UV/Vis blue lamps or UVC lamps (254 nm). H(2)O(2), FeSO(4) and TiO(2) were added at 1700, 456, and 2500 mgL(-1), respectively. trans-Chlordane was not significantly removed in non-irradiated controls and in samples irradiated with UV/Vis. It was also not removed in the absence of surfactant Triton X-114 added at 250 mgL(-1). In the presence of the surfactant, trans-chlordane concentration was reduced by 95-100% after 48 h of UVC and UVC/H(2)O(2) treatments and 70-80% after UVC/H(2)O(2)/Fe(2+), UVC/TiO(2) and UVC/H(2)O(2)/TiO(2) treatments. Based on these results, UVC, UVC/H(2)O(2) and UVC/TiO(2) treatments were further investigated. UVC treatment supported the highest pollutant removal (100% in 48 h), dechlorination efficiency (81% in 48 h), and detoxification to Lepidium sativum seed germination and activated sludge respiration although irradiated samples remained toxic to Chlorella vulgaris. Biodegradation of the UVC irradiated samples removed the source of algae toxicity but this could not be clearly attributed to the removal of trans-chlordane photoproducts because the surfactant interfered with the chemical and biological assays. Evidence was found that trans-chlordane was photodegraded through photolysis causing its successive dechlorination. trans-Chlordane removal was well described by a first order kinetic model at a rate of 0.21±0.01h(-1) at the 95% confidence interval.