Bacterial Quorum-Quenching Lactonase Hydrolyzes Fungal Mycotoxin and Reduces Pathogenicity of Penicillium Expansum. Suggesting a Mechanism of Bacterial Antagonism

Penicillium expansum is a necrotrophic wound fungal pathogen that secrets virulence factors to kill host cells and mycotoxins such as patulin. these virulence factors are modulated by intrinsic regulators and extrinsic environmental factors. Lately the molecular mechanisms of pathogenicity in P. expansum has been explored. However, less is known regarding the bacteria–fungal communication in the fruit environment that may affect pathogenicity. Many bacterial species use quorum-sensing (QS), a population density dependent regulatory mechanism, as a method to control pathogenicity. N-acyl homoserine lactones (AHLs) are Gram-negative QS signal molecules (SQMs). Enzymes degrading these QSMs, have potential antimicrobial properties. Here, we demonstrate that a bacterial AHL lactonase can efficiently degrade the fungal mycotoxin patulin, a lactone secreted by P. expansum. The bacterial lactonase hydrolyzed patulin at high catalytic efficiency, with a k_cat value of 0.724 ± 0.077 s^-1 and K_M value of 116 ± 33.98 µM. The calculated specific activity (k_cat/K_M) showed a value of 6.21 ± 10³ s^-1M^-1. Incubation of P. expansum spores with the purified lactonase inhibited pathogen colonization in apples and resulted in reduced expression of genes involved in patulin biosynthesis and fungal cell wall biosynthesis. Phylogenetic and structural analysis was used to identify putative lactonase in P. expansum. Recombinant expression and purification of the newly identified fungal enzyme verified its activity with patulin. These results indicate a possible role for patulin and lactonases in inter-kingdom communication between fungi and bacteria, and suggest that lactonases can be used as potential antifungal post-harvest treatment.