Bio-orthogonal non-canonical amino acid tagging to understand bacterial persistence

Abstract

Phenotypic heterogeneity in populations of isogenic bacterial cells includes variations in metabolic rates and responses to antibiotic treatment. In particular, sub-populations of "persister" cells exhibit increased antibiotic tolerance. Understanding the mechanisms that underlie bacterial persistence would constitute an important step toward preventing and treating chronic infections. In this work, we demonstrate the use of Bioorthogonal Noncanonical Amino Acid Tagging (BONCAT) for time- and cell state-selective proteomic anal. of cultures of Pseudomonas aeruginosa that exhibit persistence upon antibiotic treatment. Two methods were developed in the P. aeruginosa strain PA14 by treating cells either with L-azidohomoalanine (AHA) or with L-azidonorleucine (ANL). Comparing the proteomic profiles of untreated cells and persister cells showed that proteins involved in the biosynthesis of pyochelin, a secondary siderophore involved in bacterial iron acquisition, were down-regulated in the dormancy phase and up-regulated in the regrowth phase. Furthermore, regrowth behavior is altered by a gene knockout in the pyochelin pathway, but not by a knockout in the biosynthesis of pyoverdine, another siderophore generally thought to be predominant in bacterial iron acquisition. We are exploring the implications of these results with respect to the mechanisms of persistence-related phenotypic state switching.

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