Genes involved in nutrient competition by Pseudomonas putida JBC17 to suppress green mold in postharvest satsuma mandarin

Understanding the mechanisms underlying biocontrol activity in biocontrol agents is indispensable to implement biological control. However, the understanding of specific mechanisms for nutrient competition in nutrient limited environments is still limited. This study was performed to control green mold of postharvest satsuma mandarin (mandarin) using Pseudomonas putida JBC17 (JBC17), and identify the genes involved in nutrient competition. Treatment with JBC17 on wounded mandarin fruits at a concentration of 10⁶ and 10⁷cfuml^-1 suppressed the incidence of green mold with efficacy of 74.1 and 91.4%, respectively, compared to the untreated control. In spite of there being no antifungal activity in a dual culture test, JBC17 significantly inhibited the conidial germination of Penicillium digitatum. The results from the nutrient competition assay revealed that the inhibition of conidial germination was exerted by nutrient starvation. From the constructed transposon (Tn) library of JBC17, exopolyphosphatase (ppx) and Xaa-Pro aminopeptidase (pepP) were recognized as potential factors responsible for the inhibition of conidial germination. In conclusion, the understanding of nutrient depletion specific to the inhibition of conidial germination by JBC17 may ultimately lead to a deeper understanding of the bacterial metabolism and conidial metabolism for germination as well as biocontrol activity.