Discovery of the dipicolinic acid synthase in the spoilage fungus Paecilomyces reveals its role in spore heat, salt, and alkaline pH resistance

Abstract

Paecilomyces, a food spoilage fungus, releases airborne spores that are highly resistant to harsh environmental conditions, including pasteurization. In this study, dipicolinic acid (DPA), which is a common component of bacterial spores, was detected in Paecilomyces maximus conidia at concentrations from 0.1 % to 2.8 % w/w (DPA weight per spore weight). The DPA synthase (PmDpa) was identified and obtained through heterologous expression in Escherichia coli. The enzyme was iron-dependent and catalyzed the conversion of L-2,3-dihydrodipicolinate (DHD) into DPA in the presence of NAD⁺. Mutant Δpmdpa spores exhibited altered morphology and reduced resistance to heat, salinity, and alkaline pH compared to wild-type spores, indicating that PmDpa plays a key role in the structure and environmental tolerance of P. maximus spores. DPA was identified in the spores of several Paecilomyces, Aspergillus, and Penicillium strains, indicating its prevalence in the conidia of Thermoascaceae and Aspergillaceae (Eurotiales). This study identifies DPA in Eurotiales spores for the first time and highlights the first key gene associated with Paecilomyces spore resistance.