Characterisation of the nitrile hydratase gene clusters of Rhodococcus erythropolis strains AJ270 and AJ300 and Microbacterium sp. AJ115 indicates horizontal gene transfer and reveals an insertion of IS1166

The nitrile metabolising strains AJ270, AJ300 and AJ115 were isolated from the same location. The strains have very similar nitrile metabolising profiles. Sequencing of the 16S rRNA gene indicates that strains AJ270 and AJ300 are novel strains of Rhodococcus erythropolis while strain AJ115 is a novel Microbacterium strain very closely related to Microbacterium oxydans and Microbacterium liquefaciens. Analysis of the structure of the nitrile hydratase/amidase gene clusters in the three strains indicates that this region is identical in these strains and that this structure is different to other nitrile hydratase/amidase gene clusters. The major difference seen is the insertion of a complete copy of the insertion sequence IS1166 in the nhr 2 gene. This copy of IS1166 generates a 10 bp direct duplication at the point of insertion and has one ORF encoding a protein of 434 amino acids, with 98% homology to the transposase of IS666 from Mycobacterium avium. A gene oxd, encoding aldoxime dehydratase is found upstream of the nitrile hydratase gene cluster and an open reading frame encoding a protein with homology to GlnQ type ABC transporters is found downstream of the nitrile hydratase/amidase genes. The identity of the nitrile hydratase/amidase gene clusters in the three strains suggests horizontal gene transfer of this region. Analysis of the strains for both linear and circular plasmids indicates that both are present in the strains but hybridisation studies indicate that the nitrile hydratase/amidase gene cluster is chromosomally located. The nitrile hydratase/amidase enzymes of strain AJ270 are inducible with acetonitrile or acetamide. Interestingly although a number of Fe-type nitrile hydratases have been shown to be photosensitive, the enzyme from strain AJ270 is not.