Dynamics Associated with Bacteriocin Resistance in Pseudomonas syringae
Open Access
- Author:
- May, Andrew J
- Area of Honors:
- Biological Engineering
- Degree:
- Bachelor of Science
- Document Type:
- Thesis
- Thesis Supervisors:
- Kevin Loren Hockett, Thesis Supervisor
Ali Demirci, Thesis Honors Advisor - Keywords:
- bacterial resistance
plant disease
bacterial competition
biological control
bacteriocin - Abstract:
- Pseudomonas syringae pv. actinidiae (Psa BV3) has caused severe economic damage the New Zealand kiwifruit industry following its introduction in 2010. A related strain, Pseudomonas syringae pv. syringae B728a (Psy B728a), produces two toxins, an R-type (retractile, phage derived) and an S-type (soluble) bacteriocin, that are active against Psa BV3. These target Psa BV3 in a ‘conditionally redundant’ way, preventing it from developing resistance to the R-type bacteriocin while in the presence of the S-type, a system which could be used as a biocontrol strategy. To increase knowledge of this system and evaluate its biocontrol potential, this project focused on finding the gene responsible for developing S-type resistance and determining if there was a fitness cost incurred by this resistance. Twelve R- and S-type resistant mutants were developed, sequenced, and aligned with their parent strain to observe the genomic and genetic changes that had occurred. An area of about 70 genes was lost in 9 of the mutants, with another having a missense mutation in a gene in this region. The remaining two resistant strains had other mutated genes. This analysis identified the hemolysin secretion/activation, TonB dependent siderophore receptor, hflB, and PQQ-dependent catabolism-associated beta propeller genes as candidates for affecting S-type resistance. Two mutant strains had slower growth rates than the wild type while two others had growth rates that were the same. The growth rate of a slower growing strain was measured in supernatant of Psa BV3 and bacteriocin deactivated Psy B728a to observe whether normal growth was recovered since all mutants arose at the same time during generation, however no growth rate recovery was observed. This suggests that while the Psy B728a bacteriocin strategy effectively prevents resistance development, the lack of observed fitness cost could increase the risk involved with using this system as a biocontrol technique.