Cytochrome P450 BM3 of Bacillus megaterium - a possible endosulfan biotransforming gene

Evaluation of endosulfan degradation capacity by six pure strains isolated from a horticulture soil

Endosulfan is an organochlorine pesticide included in the Stockholm Convention for Persistent Organic Compounds. The utilization of endosulfan as the sole source of carbon and its mineralization was evaluated using pure strains of Bacillus subtilis, Bacillus pseudomycoides, Peribacillus simplex, Enterobacter cloacae, Achromobacter spanius, and Pseudomonas putida, isolated from soil with historical pesticide use. The consumption of the α isomer of endosulfan by five of the six strains studied was higher than 95%, while B. subtilis degraded only 76% of the initial concentration (14 mg/L). On the other hand, the degradation of the β isomer was approximately 86% of the initial concentration (6 mg/L) by B. subtilis, P. simplex, and B. pseudomycoides and 95% by P. putida, E. cloacae, and A. spanius. The ability of A. spanius, P. simplex, and B. pseudomycoides to degrade endosulfan has not been previously reported. The production of endosulfan lactone by the Bacillus strains, as well as A. spanius and P. putida, indicated that endosulfan was degraded by the hydrolytic pathway.

Bacilli-Mediated Degradation of Xenobiotic Compounds and Heavy Metals

Xenobiotic compounds are man-made compounds and widely used in dyes, drugs, pesticides, herbicides, insecticides, explosives, and other industrial chemicals. These compounds have been released into our soil and water due to anthropogenic activities and improper waste disposal practices and cause serious damage to aquatic and terrestrial ecosystems due to their toxic nature. The United States Environmental Protection Agency (USEPA) has listed several toxic substances as priority pollutants. Bacterial remediation is identified as an emerging technique to remove these substances from the environment. Many bacterial genera are actively involved in the degradation of toxic substances. Among the bacterial genera, the members of the genus Bacillus have a great potential to degrade or transform various toxic substances. Many Bacilli have been isolated and characterized by their ability to degrade or transform a wide range of compounds including both naturally occurring substances and xenobiotic compounds. This review describes the biodegradation potentials of Bacilli toward various toxic substances, including 4-chloro-2-nitrophenol, insecticides, pesticides, herbicides, explosives, drugs, polycyclic aromatic compounds, heavy metals, azo dyes, and aromatic acids. Besides, the advanced technologies used for bioremediation of environmental pollutants using Bacilli are also briefly described. This review will increase our understanding of Bacilli-mediated degradation of xenobiotic compounds and heavy metals.

The cytochrome P450BM-1 of Bacillus megaterium A14K is induced by 2,3,7,8-Tetrachlorinated dibenzo-p-dioxin: Biophysical, molecular and biochemical determinants

The current study describes biological changes in Bacillus megaterium A14K cells growing in the presence of 2,3,7,8-Tetrachlorinated dibenzo-p-dioxin (TCDD), the most potent congener of dioxins. The results indicate that the metabolizing of 2,3,7,8-TCDD by BmA14K was accompanied with a novel morphological and biophysical profile typified by the growth of single cells with high levels of biosurfactant production, surface hydrophobicity and cell membrane permeability. Moreover, the TCDD-grown bacteria exhibited a specific fatty acid profile characterized by low ratios of branched/straight chain fatty acids (BCFAs/SCFAs) and saturated/unsaturated fatty acids (SFAs/USFAs) with a specific "signature" due to the presence of branched chain unsaturated fatty acids (BCUFAs). This was synchronized with a significant induction of P450_BM-1, an unsaturated fatty acid-metabolizing enzyme in B. megaterium. Subsequently, the profile of oxygenated fatty acids in the TCDD-grown bacteria was typified by the presence of 5,6-epoxy derived from unsaturated C15, C16 and C17 fatty acids, that were absent in control bacteria. A net increase was also detected in both hydroxylated and epoxidized fatty acids, especially those derived from C15:0 and C16:1, respectively, suggesting a specific TCDD-induced "signature" of oxygenated fatty acids in BmA14K. Overall, this study sheds light on the use of B. megaterium A14K as a promising bioindicator/biodegrader of dioxins.

A newly isolated Pseudomonas sp. can degrade endosulfan via hydrolytic pathway

Endosulfan an organochlorinated pesticide was used extensively throughout the world. Its enormous and inadequate use creates environmental as well as health problems. A bacterial strain capable to utilize endosulfan as a sole source of sulfur was isolated from pesticide contaminated soil and identified as Pseudomonas sp. on the basis of 16S rRNA. Batch experiments were conducted at various initial concentrations of endosulfan, i.e. 5, 25, 50, 75 and 100 mg/l to study its rate of degradation. After three days of incubation, 70-80% of each initial concentration was degraded by the isolated strain as compared to the control. Degradation of endosulfan increased with the time of incubation and maximum degradation was observed after 5 days of incubation. GC-MS revealed that the major metabolite was endosulfan lactone, which accumulated after 5 days of incubation. Kinetic studies at various initial concentrations also revealed that the bacterium has very promising attitude to utilize endosulfan as sole source of sulfur. It was observed that the addition of auxiliary sulfur Fe(SO₄)₃ in any concentration (0.05, 0.01 and 0.1%) decreased the rate of degradation of endosulfan. The ratio of μ_max/ K_s was high (0.03 mg/l) when endosulfan was single sulfur source as compared to the value recorded when Fe(SO₄)₃ was added alongwith the endosulfan. This indicates that the newly isolated bacterium attacks sulfur moiety for its degradation.

Steroids hydroxylation catalyzed by the monooxygenase mutant 139-3 from Bacillus megaterium BM3

The search of new substrates with pharmaceutical and industrial potential for biocatalysts including cytochrome P450 enzymes is always challenging. Cytochrome P450 BM3 mutant 139-3, a versatile biocatalyst, exhibited hydroxylation activities towards fatty acids and alkanes. However, there were limited reports about its hydroxylation activity towards steroids. Herein, an Escherichia coli–based whole-cell extract containing the recombinant 139-3 protein was used as the biocatalyst to screen 13 steroids. Results revealed that 139-3 was able to specifically hydroxylate androstenedione (1) at 1α-position, generating a hydroxylated steroid 1α-OH-androstenedione (1a). To investigate whether C-1α hydroxylation catalyzed by BM3 mutant 139-3 could be industrially used, an optimization of catalyzing conditions was performed. Accordingly, the BM3 mutant 139-3 enzyme was observed to display maximum activity at 37 °C, under pH 7.0 for 4 h, with 37% transformation rate. Moreover, four 139-3 variants were generated by random mutagenesis with the aim of improving its activity and expanding substrate scope. Surprisingly, these mutants, sharing a common mutated site R379S, lost their activities towards androstenedione (1). These data clearly indicated that arginine residue located at site 379 played key role in the hydroxylation activities of 139-3. Overall, these new findings broadened the substrate scope of 139-3 enzyme, thereby expanding its potential applications as a biocatalyst on steroids hydroxylation in pharmaceutical industry.

Microbial degradation of endosulfan in contaminated soil with the elution of surfactants

In this work, an endosulfan-degrading strain was isolated from the aged soil contaminated by endosulfan, and identified as Ochrobactrum sp. EB-4 by 16S rDNA sequence analysis. The microbial degradation characteristics of endosulfan in three eluents (Tween 80 + SDS, Tween 80 + Na2SiO3, Tween 80 + SDS + Na2SiO3) were investigated. The results showed that the degradation percents of α-, β-endosulfan in the three eluents were 86.83 %∼92.91 % and 88.90 %∼93.94 % in 15 days, respectively. The degradation process can be well described by the first-order kinetic model, and the half-times of α-endosulfan in eluent 1∼eluent 3 were 3.83, 5.29, and 4.53 days, while those of β-endosulfan were 3.35, 4.50 and 3.79 days, respectively. The endosulfan diol and endosulfan sulfate as main metabolites were detected, and the former can be further degraded by this strain, which revealed that the simultaneously happened hydrolysis and oxidation reactions were the main degradation processes, and dominated by hydrolysis reaction. After 5 days of washing with the eluents, 56.00∼84.33 % of α-endosulfan, and 46.49∼68.56 % of β-endosulfan in soil were eluted, respectively, and can be entirely biodegraded in 12 days, which indicated that the microbial degradation was the rate-determining step.