New Type of Antimicrobial Protein Produced by the Plant Pathogen Clavibacter michiganensis subsp. michiganensis

Abstract

ABSTRACT It has previously been shown that the tomato pathogen Clavibacter michiganensis subsp. michiganensis secretes a 14-kDa protein, C. michiganensis subsp. michiganensis AMP-I ( Cmm AMP-I), that inhibits growth of Clavibacter michiganensis subsp. sepedonicus , the causal agent of bacterial ring rot of potato. Using sequences obtained from tryptic fragments, we have identified the gene encoding Cmm AMP-I and we have recombinantly produced the protein with an N-terminal intein tag. The gene sequence showed that Cmm AMP-I contains a typical N-terminal signal peptide for Sec-dependent secretion. The recombinant protein was highly active, with 50% growth inhibition (IC 50 ) of approximately 10 pmol, but was not toxic to potato leaves or tubers. Cmm AMP-I does not resemble any known protein and thus represents a completely new type of bacteriocin. Due to its high antimicrobial activity and its very narrow inhibitory spectrum, Cmm AMP-1 may be of interest in combating potato ring rot disease.