Endophytic and rhizoplane bacteria associated with Cytisus striatus growing on hexachlorocyclohexane-contaminated soil: isolation and characterisation

Inoculation of plants with their associated microorganisms is a promising strategy for improving phytoremediation of organic contaminants. Isolation and characterisation of these organisms from plants growing in contaminated sites will permit the identification of candidate strains for re-inoculation studies. The diversity of culturable endophytic and rhizoplane bacteria found in association with Cytisus striatus plants growing at a hexachlorocyclohexane (HCH)-contaminated site was studied. A total of 97 strains of endophytic bacteria were isolated from the root, stem and leaf tissues, and 49 from the rhizoplane. They were further characterised genotypically (BOX-PCR, 16S rDNA sequencing, presence of linA and linB genes) and phenotypically (trace metal tolerance, capacity to produce biosurfactants and plant growth promoting (PGP) traits). Proteobacteria and Actinobacteria dominated the isolate collection, and taxonomic diversity was strongly tissue-specific. The linA and linB genes were not detected in the isolate collection. The majority of isolates had at least one of the PGP traits tested, whereas biosurfactant-producing strains were less frequent. Resistance to more than one trace metal was generally restricted to endophytes isolated from shoot tissues. The PGP characteristics found in an important number of the bacterial isolates obtained in this study could be particularly useful for exploiting the phytoremediation potential of C. striatus.