Stimulation in the biodegradation of lindane and other hexachlorocyclohexane isomers by Sphingomonas D4 when grown in co-culture with biosurfactant-producing strains

ALVAREZ ANALÍA; RODRIGUEZ GARRIDO BEATRIZ; TOMÉ PÉREZ A; KIDD PETRA; PRIETO-FERNANDEZ ANGELES

Zaragoza

Workshop; 13th International HCH and Pesticides Forum; 2015

International HCH & Pesticides Association (IHPA) The Netherlands

Lindane, the gamma isomer of 1,2,3,4,5,6-hexachlorocyclohexane (-HCH) was extensively used as an insecticide. The industrial production, by chlorination of benzene and posterior purification of lindane, generated massive amounts of residues containing other HCH isomers (mainly alpha and beta). Moreover, the mixture of isomers (technical lindane) was also used as a cheap and effective insecticide, mainly in developing countries1,2. Nowadays all HCH isomers are included in the list of persistent organic pollutants (POPs) of the Stockholm Convention (2009)3 and their use is banned or restricted to specific applications in most countries. However, these contaminants are still present worldwide in soils and waters and constitute a particularly important environmental problem in the previous dumping sites close to production centres4,5.The HCH isomers differ in their physic-chemical properties (hydrophobicity, volatility, structural stability, etc.)6; determining their interactions with organic and inorganic soil components and their persistence in the environment. Beta isomer is the more hydrophobic and recalcitrant of the major HCH isomers. Biodegradation is considered the main degradation pathway of HCHs in the environment and is influenced by their availability. Several bacterial strains able to degrade HCHs have been isolated and studied. In aerobic environments members of the family Sphingomonadaceae are considered particularly important for the elimination of HCHs although other degraders have also been isolated and described 4,5,7,. In the present study the biodegradation of HCHs residue in slurries of two soils with contrasting organic matter contents (4% and 0.4% organic C) was studied. The soil slurries were inoculated with the HCH-degrading Sphingomonas D48, alone or in co-culture with Streptomyces M79 or Rhodococcus ET54b10, strains which are able to produce biosurfactants. In all soil slurries inoculated with D4 the HCHs content decreased by more than 95%. Co-inoculation of the degrader with either M7 or ET54b stimulated the dissipation of HCHs. The positive effect of the co-culture on the dissipation was mainly observed in the soil with a lower organic matter content and for the major isomers present in the HCHs residue (alpha and beta). In soil with a higher organic matter content the degradation of HCHs was very fast and the stimulating effect of co-inoculation was only significant for the beta isomer after 2 days of incubation. The results indicate that biodegradation of HCHs in the environment may probably be improved by bioaugmentation with selected bacterial consortia including HCHs degraders and strains which are able to increase the bioavailability of HCHs.