Identification of Biosynthetic Precursors and Optimization of 7-Hydroxytropolone Bioproduction by Pseudomonas sp. PA14H7.

Abstract

Cell-free supernatant of the strain Pseudomonas sp. PA14H7 has previously shown interesting activity against Soft Rot Pectobacteriaceae (SRP), the bacterial pathogen responsible for blackleg and soft rot diseases in potatoes. A deeper understanding of its mode of action is essential to optimize its use as a biocontrol agent. We previously reported that Pseudomonas sp. PA14H7 produces a specialized metabolite, the 7-hydroxytropolone (7-HT), which acts as an iron chelator, limiting the growth of SRP. In this study, we have constructed a Δhts10 deletion mutant of Pseudomonas sp. PA14H7, encoding a putative acyl-CoA dehydrogenase corresponding to the ortholog of orf10 in Pseudomonas donghuensis. We demonstrated that this mutant was deficient in 7-HT biosynthesis, confirming that this molecule is the metabolite responsible for the antagonist activity. After finding a minimum culture medium (MK) allowing the Pseudomonas sp. PA14H7 growth without 7-HT production, we investigated the biosynthetic pathway of this metabolite. We identified phenylalanine and phenylacetic acid as 7-HT precursors and demonstrated that the addition of 150 mg/L of phenylalanine to the MK medium enhanced the 7-HT bioproduction by Pseudomonas sp. PA14H7 up to 30 mg/L. These findings provide new insights into the biosynthesis and regulation of 7-HT, paving the way for the use of Pseudomonas sp. PA14H7 as a biocontrol agent.