Growth of dechlorinating bacteria in enrichment cultures, derived from contaminated soil and sediment from Guadeloupe that dechlorinate hexachlorocyclohexane isomers.

International audienceHexachlorocyclohexane (HCH) isomers are polychlorinated organic compounds of environmental concern. A mixture of different HCH isomers (α, β, δ and γ), known as technical-grade HCH and γ-HCH (lindane) were extensively used as pesticides in banana plantations in the French West Indies. HCH molecules are chemically stable. Beta-HCH, is the most difficult isomer to degrade in both water and soil. HCH isomers can be subjected to microbial biodegradation. However, to date, the anaerobic biotransformation of HCH isomers is not well characterized. The growth of specific bacterial genera involved in the dechlorination of HCH isomers has yet to be demonstrated. We aimed to identify the bacterial populations that grow as a result of the dechlorination of α-HCH and β-HCH. Dechlorination products were measured and liquid culture was sampled for DNA extraction as well. Previous sequencing studies had identified Dehalobacter and Geobacter as candidate dechlorinators in the α-HCH and β-HCH enrichment cultures. Dehalobacter is known to be a genus capable of dechlorinating β-HCH. Thus, we performed quantitative Polymerase Chain Reaction (qPCR) to track the growth of Dehalobacter during the dechlorination of β-HCH and α-HCH. We will perform qPCR for Geobacter as well.The final stable products of the dechlorination of α-HCH and β-HCH were benzene and monochlorobenzene (MCB). For the α-HCH cultures, the relative abundance of Dehalobacter increased from 2.18%±1.9% on day 0 to 34.66%±7.6% on day 63. For the β-HCH cultures, Dehalobacter increased from 1.21%±1.1% on day 0 to 13.52%±4.8% on day 63. So far, we can conclude that Dehalobacter spp. are involved in the dechlorination of these isomers. We expect to have the qPCR results for Geobacter. It is conceivable to have both Dehalobacter and Geobacter involved in the dechlorination of α-HCH and β-HCH. Knowledge on the microorganisms that can dechlorinate HCH isomers is essential for the application of potential bioremediation approaches