Pectobacterium versatile β-lactamase, a common good of the soft rot Pectobacteriaceae (SRP) species complex

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 _PEC-1 β-lactamase. The aim of our work was to analyse the role of BlaPEC-1 during plant infection. To this end, two bla _PEC-1 -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 _PEC-1 enables P. versatile to resist ampicillin or the carbapenem produced by Pectobacterium brasiliense . In mono-infections of potato tubers, bla _PEC-1 -deleted strains were not affected in virulence, fitness or association with bacterial commensals. In mixed infections, Bla _PEC-1 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 when Bla _PEC1 -expressing bacteria were a minority within the symptom. These results indicate that Bla _PEC -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.