Molecular approaches to understand the effect of acetic acid in uropathogenic E. coli

Acetic acid has long been known for its antibacterial activity. We are using TraDIS to investigate the molecular mechanisms by which acetic acid acts as an antibacterial agent. To do this, we grew a high-density transposon library in uropathogenic E. coli EO499 serotype 131 in M9 media at pH 7 and pH 5.5 with acetic acid concentrations of 40 mM and 4 mM, respectively, or without added acetic acid. Sequencing libraries were generated from total bacterial populations after growth, and sequenced using a transposon-specific primer to generate positions and frequencies for each transposon. By comparing numbers of reads before and after the stress, we identified candidate genes where transposon inserts led to a decrease of fitness under acetic acid stress. Eight of these were chosen for further study: nuoM, nuoG, sucA, sthA, pitA, apaH, rssB and ytfP. Because of the difficulties of constructing gene deletions in the uropathogenic strain for validating the TraDIS results, we tested the relative fitness of the corresponding gene deletion mutants from the Keio library (in strain BW25113), with the growth conditions used for EO499. Interestingly, only a few knockouts showed a reduction in relative fitness in time course competitions at pH 5.5 with acetic acid. This may due to the differences between strains used in TraDIS and competition. To overcome this issue, we have also isolated transposon mutants from E. coli EO499 transposon library for the determination of relative fitness. The results will be presented.