Zinc is an important nutrient but can be lacking in some soil environments, influencing the physiology of soil-dwelling bacteria. Hence, we studied the global effect of zinc limitation on the transcriptome of the rhizosphere biocontrol strain Pseudomonas protegens Pf-5 (formerly Pseudomonas fluorescens). We observed that the expression of the putative zinc uptake regulator (Zur) gene was upregulated, and we mapped putative Zur binding sites in the Pf-5 genome using bioinformatic approaches. In line with the need to regulate intracellular zinc concentrations, an array of potential zinc transporter genes was found to be zinc-regulated. To adapt to low-zinc conditions, a gene cluster encoding non-zinc-requiring paralogues of zinc-dependent proteins was also significantly upregulated. Similarly, transcription of genes encoding non-zinc-requiring paralogues of ribosomal proteins L31 and L36 was increased by zinc limitation. A strong transcriptional downregulation of the putative copper chaperone gene (copZ) was also observed, suggesting interplay between zinc and copper homeostasis. Importantly, zinc also affected biocontrol attributes in Pf-5, most notably reducing the expression of the gene cluster responsible for biosynthesis of the antibiotic 2,4-diacetylphloroglucinol (DAPG) under zinc limitation. This study clearly defines changes to the molecular physiology of Pf-5 that enable it to survive under zinc limitation.
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