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. 2020 Nov 9:11:590061.
doi: 10.3389/fmicb.2020.590061. eCollection 2020.

Genetic Analysis of Citrobacter sp.86 Reveals Involvement of Corrinoids in Chlordecone and Lindane Biotransformations

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Genetic Analysis of Citrobacter sp.86 Reveals Involvement of Corrinoids in Chlordecone and Lindane Biotransformations

Agnès Barbance et al. Front Microbiol. .

Abstract

Chlordecone (Kepone®) and γ-hexachlorocyclohexane (γ-HCH or lindane) have been used for decades in the French West Indies (FWI) resulting in long-term soil and water pollution. In a previous work, we have identified a new Citrobacter species (sp.86) that is able to transform chlordecone into numerous products under anaerobic conditions. No homologs to known reductive dehalogenases or other candidate genes were found in the genome sequence of Citrobacter sp.86. However, a complete anaerobic pathway for cobalamin biosynthesis was identified. In this study, we investigated whether cobalamin or intermediates of cobalamin biosynthesis was required for chlordecone microbiological transformation. For this purpose, we constructed a set of four Citrobacter sp.86 mutant strains defective in several genes belonging to the anaerobic cobalamin biosynthesis pathway. We monitored chlordecone and its transformation products (TPs) during long-term incubation in liquid cultures under anaerobic conditions. Chlordecone TPs were detected in the case of cobalamin-producing Citrobacter sp.86 wild-type strain but also in the case of mutants able to produce corrinoids devoid of lower ligand. In contrast, mutants unable to insert the cobalt atom in precorrin-2 did not induce any transformation of chlordecone. In addition, it was found that lindane, previously shown to be anaerobically transformed by Citrobacter freundii without evidence of a mechanism, was also degraded in the presence of the wild-type strain of Citrobacter sp.86. The lindane degradation abilities of the various Citrobacter sp.86 mutant strains paralleled chlordecone transformation. The present study shows the involvement of cobalt-containing corrinoids in the microbial degradation of chlorinated compounds with different chemical structures. Their increased production in contaminated environments could accelerate the decontamination processes.

Keywords: Citrobacter; chlordecone; cobalamin; corrinoid; dechlorination; degradation; gene deletion; lindane.

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Figures

Figure 1
Figure 1
(A) Chemical structure of chlordecone mostly present under its hydrated form Wilson and Zehr (1978). (B) Chemical structure of γ-hexachlorocyclohexane (lindane).
Figure 2
Figure 2
(A) Genetic organization of the main Citrobacter sp.86 anaerobic cobalamin biosynthesis gene cluster. The regions targeted for the deletion of one to three consecutive genes and replacement with an antibiotic resistance marker gene − see section the Materials and Methods − are shown. (B) Anaerobic cobalamin biosynthesis pathway in Citrobacter sp.86 based on genome annotation (*cbiP, synonym name for cobQ). Reactions blocked in the mutant strains are shown by crosses. **In the anaerobic pathway, there is no dedicated enzyme for cobalt reduction (Fonseca and Escalante-Semerena, 2000).
Figure 3
Figure 3
Transformation of chlordecone in Citrobacter sp.86 wild-type and mutant strain cultures over the time. GC-MS chromatograms (full scan mode) of extracted cultures at selected times incubated with (A) Citrobacter sp.86 wild-type, (B) ΔcobQUS mutant strain, (C) ΔcobST mutant strain, (D) ΔcbiHJK mutant strain, (E) ΔcbiK mutant strain, and (F) without bacteria (abiotic control). Numeric data of peak areas are available in Supplementary Material. The various mutant strains and the negative control (abiotic control) were incubated under the same conditions. For more clarity, a single chromatogram is displayed among the duplicates for each selected time.
Figure 4
Figure 4
Transformation of lindane in Citrobacter sp.86 wild-type and mutant strain cultures over the time. HS-GC-MS extracted ion chromatograms (m/z = 181, 147, 146, 112, and 78, searched for each condition) of sampled cultures at selected times incubated with (A) Citrobacter sp.86 wild-type, (B) ΔcobQUS mutant strain, (C) ΔcbiHJK mutant strain, (D) ΔcbiK mutant strain, and (E) without bacteria (abiotic control). Numeric data of peak areas are available in Supplementary Material. The various mutant strains and the negative control (abiotic control) were incubated under the same conditions. For more clarity, a single chromatogram is displayed among the duplicates at each selected time.
Figure 5
Figure 5
Abiotic transformation of lindane in neutral and basic conditions. HS-GC-MS extracted ion chromatograms (m/z = 181, 147, 146, 112, and 78, searched for each condition) after 21 days of abiotic cultures at different pH: 7, 7.5, 8, and 9. Numeric data of peak areas are available in Supplementary Material.

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