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POSTERS: Molecular plant-microbe interactions

Evidence of physiological tolerance and heterogenous resistance to a phage-tail like bacteriocin in Pseudomonas syringae
Prem Kandel - The Pennsylvania State University. Kevin Hockett- The Pennsylvania State University

Bacteriocins are bacterially-produced, narrow-spectrum, antimicrobial proteins that are proposed as antibiotic alternatives. Long-term use of bacteriocins in pathogen control requires understanding of various survival mechanisms the target cells use against bacteriocins. We utilized the model plant pathogen, Pseudomonas syringae, where we exposed P. syringae pv. phaseolicola (Pph) cells to partially-purified bacteriocin of P. syringae pv. syringae B728a. Pph cells at two growth stages were exposed to bacteriocin and surviving population enumerated 1, 4, 8, and 24 hours post-treatment. Significantly higher survival was obtained with stationary than the log cells. Upon re-exposure, majority of the cells did not gain any detectable resistance, indicating survival by tolerance mechanism. We also recovered a high-tolerant mutant with increased bacteriocin survival. Bacteriocin treatment also selected complete and incomplete resistant mutants that differed in bacteriocin sensitivity. By genome sequencing, we identified various lipopolysaccharide related genes as the candidates for resistant and a hypothetical protein containing a signal peptide and ten trans-membrane domains for the high-tolerant mutant. Moreover, by lipopolysaccharide analysis, we showed that the complete resistant mutants lack the lipopolysaccharide O-antigen, while the incomplete resistant and high-tolerant mutants contain the O-antigen but likely in an altered form to survive bacteriocins.