Biological function of the pld gene product that degrades -poly-l-lysine in Streptomyces albulus

ε-Poly-l-lysine (ε-PL) is one of the few naturally occurring biopolymers and is characterized by a peptide bond between the α-carboxyl and ε-amino groups. Previously, we purified and characterized the ε-PL-degrading enzyme (Pld) from Streptomyces albulus, which is an ε-PL producer, and this enzyme was expected to confer self-resistance to the ε-PL produced by the organism itself. The gene encoding Pld was cloned based on the N-terminal amino acid sequence determined in this study, and a sequencing analysis revealed eight open reading frames (ORFs), i.e., ORF1 to ORF8 in the flanking region surrounding the pld gene (present in ORF5). To investigate the biological function of Pld, we constructed a knockout mutant in which the pld gene is inactivated. Studies on ε-PL susceptibility, ε-PL-degrading activity, and ε-PL productivity demonstrated that the pld gene does play a partial role in self-resistance and that S. albulus was found to produce other ε-PL-degrading enzyme(s) in addition to Pld. To the best of our knowledge, this is the first report on a self-resistance gene for a biopolymer possessing antibacterial activity.