APS Homepage

Poster: Biology & Disease Mgmt: Biological Control


Amino acids influence antibiotic production by Pantoea vagans strain C9-1
J. KLEIN (1), V. Stockwell (2), J. Loper (2) (1) Oregon State University, U.S.A.; (2) USDA-ARS, Horticultural Crops Research Unit, U.S.A.

Pantoea vagans strain C9-1 is an effective biological control agent for fire blight caused by Erwinia amylovora. C9-1 is thought to suppress E. amylovora on stigmas via resource competition and production of the antibiotics pantocin A (formerly herbicolin O) and herbicolin I. We used a green fluorescent protein reporter construct in C9-1 to monitor the regulation of the promoter of the pantocin A operon (paaPABC) on solidified media and in broth culture with a Tecan Infinite M200PRO. In assays on solidified media, inhibition of E. amylovora by C9-1 and expression of the gfp reporter for pantocin A operon was detected on Neidhardt’s modified medium, but not on Luria Bertani (LB) medium. Addition of yeast extract or tryptone (components of LB) to Neidhardt’s broth medium suppressed the expression of the pantocin A promoter. We tested the effect of various amino acids (100 mM) added to Neidhardt’s broth medium on expression of the paaPABC promoter in C9-1. We found that arginine, histidine, or tryptophan reduced expression of the pantocin A promoter compared to expression in non-amended Neidhardt’s broth medium, whereas asparagine, aspartic acid, or proline upregulated expression. Asparagine and proline are two major amino acids reported on apple and pear flower stigmas. These results indicate that the chemical environment of stigmas likely would support expression of the paaPABC operon and pantocin A biosynthesis by the biological control agent C9-1.