Genetic and Phenotypic Study of the Pectobacterium versatile Beta-Lactamase, the Enzyme Most Similar to the Plasmid-Encoded TEM-1

摘要

This study aimed to compare the chromosomal beta-lactamase from Pectobacterium versatile, PEC-1, with the well-known and globally distributed TEM-1 in terms of genetic and functional properties. Despite the similarities between the enzymes, we obtained no definitive proof of gene transfer for the emergence of bla(PEC-1) from bla(TEM-1). Genus Pectobacterium bacteria include important agricultural pathogens. Pectobacterium versatile isolates contain a chromosome-borne beta-lactamase, PEC-1. This enzyme is the closest relative of TEM-1, a plasmid-borne beta-lactamase widespread in the Enterobacterales. We performed bioinformatics and phenotypic analyses to investigate the genetic and phenotypic features of PEC-1 and its frequency and ability to spread within genus Pectobacterium. We also compared the characteristics of PEC-1 and TEM-1 and evaluated the likelihood of transfer. We found that bla(PEC-1) was present principally in a small number of genetic environments in P. versatile. Identical bla(PEC-1) genetic environments were present in closely related species, consistent with the high frequency of genetic exchange within the genus Pectobacterium. Despite the similarities between PEC-1 and TEM-1, their genetic environments displayed no significant identity, suggesting an absence of recent transfer. Phenotypic analyses on clonal constructs revealed similar hydrolysis spectra. Our results suggest that P. versatile is the main reservoir of PEC-1, which seems to transfer to closely related species. The genetic distance between PEC-1 and TEM-1, and the lack of conserved elements in their genetic environments, suggest that any transfer that may have occurred must have taken place well before the antibiotic era. IMPORTANCE This study aimed to compare the chromosomal beta-lactamase from Pectobacterium versatile, PEC-1, with the well-known and globally distributed TEM-1 in terms of genetic and functional properties. Despite the similarities between the enzymes, we obtained no definitive proof of gene transfer for the emergence of bla(PEC-1) from bla(TEM-1). Indeed, given the limited degree of sequence identity and the absence of a common genetic environment, it seems unlikely that any transfer of this gene has occurred recently. However, although bla(PEC-1) was found mostly in one specific clade of the P. versatile species, certain isolates from other closely related species, such as Pectobacterium brasiliense and Pectobacterium polaris, may also carry this gene inserted into common genetic environments. This observation suggests that genetic exchanges are frequent, accounting for the diffusion of bla(PEC-1) between isolates from different Pectobacterium species and, potentially, to exogenous mobile genetic elements.