Improving performance of Cytisus striatus on substrates contaminated with hexachlorocyclohexane (HCH) isomers using bacterial inoculants: developing a phytoremediation strategy

Microbe-assisted phytoremediation is particularly effective for organic pollutants. The leguminous shrub Cytisus striatus (Hill) Rothm. has been proposed as a candidate species for the rhizoremediation of hexachlorocyclohexane (HCH)-contaminated sites. The aim of this study was to improve the performance of this species using microbial inoculants. C. striatus was grown in substrates contaminated with 0, 10 and 35 mg HCH kg(-1) for 8 weeks. Plants were either not inoculated (NI), or inoculated with the endophyte Rhodococcus erythropolis ET54b and the HCH-degrader Sphingomonas sp. D4 (isolated from a HCH-contaminated soil) on their own or in combination (ET, D4 and ETD4). Inoculation with both bacterial strains (ETD4) resulted in decreased HCH phytotoxicity and improved plant growth. HCH-exposed plants inoculated with ETD4 presented a 120-160 % increase in root, and 140-160 % increase in shoot biomass, and led to a decrease in the activities of enzymes involved in anti-oxidative defence. APOD activity was reduced by up to 37 % in shoot tissues and 25 % in root tissues, and corresponding activities of SOD were reduced by up to 35 % and 30 %. HCH dissipation was enhanced in the presence of C. striatus but no significant effect of microbial inoculants was observed. Inoculating C. striatus with this combination of bacterial strains is a promising approach for the remediation of HCH-contaminated sites.