DNA inversion in the tail fiber gene alters the host range specificity of carotovoricin Er, a phage-tail-like bacteriocin of phytopathogenic Erwinia carotovora subsp carotovora Er

Carotovoricin Er is a phage-tail-like bacteriocin produced by Erwinia carot ovora subsp. carotovora strain Er, a causative agent for soft rot disease i n plants. Here we studied binding and killing spectra of carotovoricin Er p reparations for various strains of the bacterium (strains 645Ar, EC-2, N786 , and P7) and found that the preparations contain two types of carotovorici n Er with different host specificities; carotovoricin Era. possessing a tai l fiber protein of 68 kDa killed strains 645Ar and EC-2,,while carotovorici n Erb with a tail fiber protein of 76 kDa killed strains N786 and P7. The t ail fiber proteins of 68 and 76 kDa had identical N-terminal amino acid seq uences for at least 11 residues. A search of the carotovoricin Er region in the chromosome of strain Er indicated the occurrence of a DNA inversion sy stem for the tail fiber protein consisting of (i) two 26-bp inverted repeat s inside and downstream of the tail fiber gene that flank a 790-bp fragment and (ii) a putative DNA invertase gene with a 90-bp recombinational enhanc er sequence. In fact, when a 1,400-bp region containing the 790-bp fragment was amplified by a PCR using the chromosomal DNA of strain Er as the templ ate, both the forward and the reverse nucleotide sequences of the 790-bp fr agment were detected. DNA inversion of the 790-bp fragment also occurred in Escherichia coli DH5 alpha when two compatible plasmids carrying either th e 790-bp fragment or the invertase gene were cotransformed into the bacteri um. Furthermore, hybrid carotovoricin CGE possessing the tail fiber protein of 68 or 76 kDa exhibited a host range specificity corresponding to that o f carotovoricin Era or Erb, respectively. Thus, a DNA inversion altered the C-terminal part of the tail fiber protein of carotovoricin Er, altering th e host range specificity of the bacteriocin.