Genetic and Structural Characterization of Pneumolancidin, a Broad Spectrum Inhibitory Lantibiotic, Produced by Streptococcus pneumoniae.
Year: 2016
Type: dissertation
Abstract: Streptococcus pneumoniae, a member of the diverse microbial community of the human nasopharynx, is subjected to competitive interactions. Since colonization is a prerequisite for pneumococcal pathogenesis, understanding the dynamics of bacterial competition is important for identifying factors that aid in colonization and carriage. To eliminate competitors, pneumococcus is known to secrete antimicrobial peptides or bacteriocins. Pneumococcal bacteriocins and their role in competition have been well characterized. However, a class of modified bacteriocins named lantibiotics, and their role in promoting pneumococcal competition is less well understood. Though several lantibiotic loci have been identified in pneumococcus, none have been found with antimicrobial activity. Recently, our laboratory identified a clinical isolate of pneumococcus, P174, with a broad spectrum of inhibitory activity attributed to a novel lantibiotic locus, termed pneumolancidin (pld). In addition to encoding genes required for the modification, processing, regulation and immunity to lantibiotic peptides, four open reading frames predicted to encode four highly homologous lantibiotic peptides were also found. This posed the question of whether the Pld peptides were redundant in function or had specialized roles. Lantibiotic peptides are known to function as antimicrobials and autoinducers. To determine the role of each peptide as it relates to inhibition and induction, individual in-frame peptide deletions were constructed. Strains carrying the mutation were assayed for their ability to inhibit the growth of other strains and their ability to upregulate the pld locus. The first three peptides, PldA1-3, were found to be required for signaling while PldA4 was found to be dispensable. Because upregulation of the locus is needed to determine whether specific peptides were involved in inhibition, the ability of the peptide deletion strains to inhibit could not be evaluated. However, a serendipitous mutant, P174act, was discovered that allowed for distinct phenotypes to be observed for each of the Pld peptide deletion strains. Through structural elucidation, it was found that PldA1 and PldA3 are structurally similar yet have specialized roles in signaling and inhibition, respectively. The Pld peptides represent a novel strategy for bacterial competition and provide insight into structure-function relationships of lantibiotics.
Author: Natalie Maricic
Language: English
Subfield: Microbiology
Field: Immunology and Microbiology
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W2572695089