Identification and characterisation of behavioural genes of agrobacterium tumefaciens.

Abstract

Three behavioural mutants (fla-8, mot-6 and cheL) generated by transposon Tn5 mutagenesis and localised on cosmid pDUB1905 were studied. The cosmid pDUB1905, from a representative genomic library of the Agrobacterium tumefaciens C58C1 chromosome has previously been partly mapped and found to contain genes concerned with flagella. In this study a region of 5860 nucleotides from a 12 kb BamHl fragment of cosmid pDUB1905 was sequenced completely in both directions. Homology searches of this sequence with sequence databases and other computer analysis revealed two flagellar-related genes (flhA and fliR), a chemotactic gene (cheL) and four open reading frames (orfX, orfW, orfY and orfZ) with no significant sequence identity to any open reading frame in databases. A putative promoter-like sequence was also found upstream of orfZ. The FlhA and FliR are the inner members of type III flagellum-specific export apparatus which are responsible for delivering the flagellar subunits lacking a signal peptide leader to the surface of the cell. These have counterparts in the type III secretion proteins system responsible for transporting pathogen proteins to host cells. The function of CheL has not yet been identified. Three ORFs have chaperone characteristics. A mutant was created by insertion of a neomycin resistance cassette in the fliR homologue to determine the effects of the gene on motility. Phenotype analysis of the mutant showed no flagella and motility with small swarming pattern comparing to wild type, indicating that fliR is indeed a flagellar gene. In this study two more members of flagellum-specific export, a chemotactic gene, three open reading frames which could have specific chaperon activity, and an unknown open reading frame were identified in A. tumefaciens C58C'.