Pectobacterium versatile β-Lactamase Contributes to Soft Rot Pectobacteriaceae (SRP) Community Diversity During Potato Infection.

Little is known about the role of antibiotics in microbial ecosystems in the absence of clinical antibiotic pressure. The soft rot Pectobacteriaceae (SRP) species complex comprises 37 bacterial species that are collectively responsible for severe plant decay in many crops. Within this complex, Pectobacterium versatile strains harbour the Bla β-lactamase. The aim of our work was to analyse the role of BlaPEC-1 during plant infection. To this end, two bla-deleted strains were compared with their wild-type counterparts in vitro and in mono- or mixed infections of potato tubers with different SRP strains. In vitro, Bla enables P. versatile to resist ampicillin or the carbapenem produced by Pectobacterium brasiliense. In mono-infections of potato tubers, bla-deleted strains were not affected in virulence, fitness, or association with bacterial commensals. In mixed infections, Bla was required for the coexistence of P. versatile with the carbapenem-producing strain and was necessary to rescue carbapenem-sensitive strains both in vitro and in planta. Protection was observed even if both the bla gene was repressed and the Bla-expressing bacteria were a minority in the symptoms. These results indicate that Bla-1 exerts a true β-lactamase function during the infection process and acts as a public good of the SRP species complex to maintain SRP strain diversity.