ARS | Publication request: Effect of tannic acid on the transcriptome of the soil bacterium Pseudomonas protegens Pf-5

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 18, 2013
Publication Date: N/A

Interpretive Summary: Biological control provides a promising strategy for managing plant diseases but has not yet been utilized widely in agriculture due, in part, to unexplained variation in its success in managing disease. Our research goals are to identify sources of variation in biological control and devise ways to make it more reliable. Specifically, we focus on Pseudomonas protegens strain Pf-5, a group of bacteria that live on plant seeds and roots and protect the plant from infection by plant pathogens that live in the soil. In this study, we determined the effects of tannic acid, a compound that is produced by plants and is prevalent on plant surfaces and in soil, on the expression of all of the genes in Pf-5, including genes required for biological control. Overall, our study showed that tannic acid has wide-ranging effects on the physiology and secondary metabolism of the soil biocontrol bacterium P. protegens Pf-5.

Technical Abstract: Tannins are plant-produced organic compounds that are found in soils, are able to sequester iron, and have antimicrobial properties. We studied the effect of tannic acid on the molecular physiology of the soil-inhabiting biocontrol bacterium Pseudomonas protegens Pf-5 (formerly Pseudomonas fluorescens). We performed transcriptomic analysis of Pf-5 treated with both low and high concentrations of tannic acid. Transcription of genes involved in iron homeostasis was found to be affected by tannic acid treatment and included increased expression of siderophore biosynthesis and uptake genes. In addition, zinc homeostasis was affected based on elevated transcription for genes encoding a putative zinc uptake regular (Zur) and the zinc-independent ribosomal protein L31. Interestingly, treatment with a low concentration of tannic acid enhanced transcription of sulfur-related metabolism and transporter genes, while higher concentrations resulted in transcriptional repression of biosynthetic genes for bioactive secondary metabolites such as pyrrolnitrin, pyoluteorin and rhizoxin analogs. Furthermore, the tannic acid reduced swarming motility of Pf-5 as well as transcription of many genes required for motility. In addition, tannic acid reduced biofilm formation. Overall, our study showed that tannic acid could have a wide-ranging effect on the physiology and secondary metabolism of the soil biocontrol bacterium P. protegens Pf-5.