Location: Horticultural Crops ResearchTitle: Nutritional environment influences transcription of a pantocin A biosynthesis gene in Pantoea vagans strain C9-1 Author
Submitted to: Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/4/2017
Publication Date: 8/4/2017
Citation: Klein, J.M., Wong, P., Loper, J.E., Stockwell, V.O. 2017. Nutritional environment influences transcription of a pantocin A biosynthesis gene in Pantoea vagans strain C9-1. Journal of Plant Pathology. doi: 10.4454/jpp.v99i0.3911. Interpretive Summary: Pantoea spp. bacterial biological control agents are effective for prevention of the damaging bacterial plant disease called fire blight of pear and apple caused by Erwinia amylovora. The biological control bacteria colonization of plant tissues by the pathogen by competition for nutrients and production of compounds (antibiotics) that inhibit the growth of the pathogen. One of the antibiotics is ineffective in assays conducted on media containing proteins or if the amino acid histidine is present. It was not known if the complex proteins or amino acids inhibited production of the antibiotic by the Pantoea spp. or just reduced sensitivity of the pathogen to the effects of the antibiotic. We constructed a green fluorescent reporter that makes the Pantoea biocontrol glow green when its antibiotic biosynthesis genes are turned on. We used this reporter bacterium to study the influence of amino acids on antibiotic production. We found that certain amino acids can reduce production of the antibiotic, but those amino acids are not present in high concentrations on pear and apple. Other amino acids that are in high concentrations on apple and pear stimulate production of the antibiotic, indicating that the inhibitory compounds are likely produced on plant tissues by the biocontrol bacterium. This research provides new information on the nutritional factors influencing antibiotic production by bacterial biological control agents and may be applied to improve biological control of damaging plant diseases like fire blight of pear and apple.
Technical Abstract: The histidine-reversible antibiotic pantocin A is produced by Pantoea vagans strain C9-1 and Pantoea agglomerans strains Eh252, EH318 and P10c and contributes significantly to efficacy of biological control of fire blight of pear and apple flowers caused by Erwinia amylovora. Antibiosis by pantocin A is observed on solidified defined media, such as MGA (MOPS gluconate medium amended with asparagine), but not on the solidified peptide-rich medium lysogeny broth (LB). It was not known if lack of antibiosis on LB was due to lack of pantocin A biosynthesis or to histidine in the medium reversing the effects of pantocin A. We used a green fluorescent protein (GFP) promoter probe in C9-1 to monitor transcription of the pantocin A biosynthesis gene paaA. GFP expression was higher in MGA than in LB. Addition of yeast extract or tryptone, components in LB, to MGA significantly decreased transcription of paaA. The observed lack of inhibition of E. amylovora by C9-1 in LB was positively correlated with paaA transcription. Addition of histidine or arginine, amino acids scarce on pome fruit stigmas, to MOPS gluconate medium (MG) decreased transcription of paaA compared to MG without amino acids. In contrast, asparagine and proline, amino acids that are abundant on pome fruit stigmas supported bacterial growth and transcription of paaA, which is in agreement with findings that pantocin A production is a key component of fire blight control by Pantoea spp. on floral stigmas.