PRESENCE OF GENES HOMOLOGOUS TO THOSE NECESSARY FOR SYNTHESIS OF MICROCIN MccEh252 IN STRAINS OF PANTOEA AGGLOMERANS

Pantoea agglomerans (ex Erwinia herbicola) Eh252 produces MccEh252, a microcin that has been shown to be involved in the control of fire blight in the laboratory and in the field. Analysis of the DNA sequence of the genes necessary for the production of this microcin revealed three open reading frames (ORFs) called mpaA-C. These ORFs share a high level of similarity (97 to 99%) to paaA, paaB and paaC, three genes involved in the synthesis of pantocin A, a compound that inhibits E. amylovora and is produced by the strain of P. agglomerans Eh 318. Sequences similar to paaP, the precursor of pantocin A, were also found in Eh252. DNA fragments showing 96–99% homology to mpaA-C and mpaP were amplified from strains of P. agglomerans isolated from the USA, Europe and New Zealand using two primers (MpaF and MpaR) designed on the DNA sequence from Eh252. Among those strains was C9-1, a biological control agent for fire blight that produces herbicolin 0, a compound with similarities to both MccEh252 and pantocin A. Some differences in the range of activity and in the physico-chemical characteristics of these three compounds have been previously published. However, in this study no difference in the range of activity between these compounds could be confirmed and some of the discrepancies in the characteristics of these compounds, such as lability to high temperatures, could be in part explained by the methods used by the different laboratories.