Poly-γ-
glutamate (γ-
PGA) is an industrially interesting
polymer secreted mainly by members of the class Bacilli which forms a shield able to protect bacteria from phagocytosis and phages. Few
enzymes are known to degrade γ-
PGA; among them is a phage-encoded γ-
PGA hydrolase, PghP. The supposed role of PghP in phages is to ensure access to the surface of bacterial cells by dismantling the γ-
PGA barrier. We identified four unannotated B. subtilis genes through similarity of their encoded products to PghP; in fact these genes reside in prophage elements of B. subtilis genome. The recombinant products of two of them demonstrate efficient
polymer degradation, confirming that sequence similarity reflects functional homology. Genes encoding similar γ-
PGA hydrolases were identified in phages specific for the order Bacillales and in numerous microbial genomes, not only belonging to that order. The distribution of the γ-
PGA biosynthesis operon was also investigated with a bioinformatics approach; it was found that the list of organisms endowed with γ-
PGA biosynthetic functions is larger than expected and includes several pathogenic species. Moreover in non-Bacillales bacteria the predicted γ-
PGA hydrolase genes are preferentially found in species that do not have the genetic asset for
polymer production. Our findings suggest that γ-
PGA hydrolase genes might have spread across microbial genomes via horizontal exchanges rather than via phage
infection. We hypothesize that, in natural habitats rich in γ-
PGA supplied by producer organisms, the availability of
hydrolases that release
glutamate oligomers from γ-
PGA might be a beneficial trait under positive selection.