Screening and isolation of γ-hexachlorocyclohexane degrading bacteria from contaminated soil in Kenya

Abstract

The organochlorine insecticide Lindane is the γ-isomer of hexachlorocyclohexane (HCH). It is among the most distributed and frequently detected organochlorine pollutants in the environment. Consequently it has been flagged down for regulatory intervention and efforts are being made to eliminate it from the environment. Among the approaches proposed, bioremediation has been put forward as a promising environmental friendly approach. In line with this mission, the aim of this work was to isolate and identify bacteria able to utilize Gamma-1, 2,3,4,5,6hexachlorocyclohexane (γ-HCH) as a sole carbon source, and thus potential bioremediation agents. Using soil sample collected from a site contaminated with organochlorine pesticide, three isolates identified by 16S rRNA gene sequencing as Achromobacter sp. (isolate 1 and isolate 3) and Stenotrophomonas sp. (isolate 2) were observed to grow in minimal salt media containing γ-HCH as the sole carbon. They were all observed to be gram-negative rods that formed circular convex shaped colonies on nutrient agar. Their optimal growth temperature and pH was found to be 37 oC and 7 respectively. Growth of these isolates in minimal salt media containing γHCH as the sole carbon source after 10 days indicated reductions of γ-HCH by 84%, 35% and 51% in Isolates 1, 2 and 3 respectively. The three isolates are being reported for the first time as able to degrade γ-HCH. In the future, these microorganisms should be further investigated to establish the pathway and extent to which they degrade γ-HCH. In addition to this, their potential to degrade other persistent organochlorine insecticides and HCH isomers could be evaluated. This will be helpful in determining their potential use as non-polluting bio-agents that rapidly detoxify and/or mineralize recalcitrant and obsolete chlorinated organic pesticides.