ABSTRACT
ABSTRACT Two heptapeptides with broad antifungal activity were identified and assessed for their ability to act synergistically with thiabendazole. The hexapeptide 66-10 was the progenitor of the heptapeptides and exhibited minimal inhibitory concentrations (MICs) of 9.3 to 9.8 mug/ml for thiabendazole (TBZ) resistant Fusarium sambucinum strains (MIC of 186 to 312 mug/ml). Heptapeptide derivatives 77-3 and 77-12 exhibited MICs between 3.8 and 7.5 mug/ml against the same strains. Incubation of conidia or mycelia with the peptide 77-3 showed that treated fungal structures were stained by the membrane impermeant dye SYTOX Green indicating disruption of membranes. Conidia incubated with peptide 77-3 at 10 mug/ml showed a 91 +/- 3.6% reduction in viability in 15 min. A checkerboard method was used to test the peptides and TBZ individually and in combination to determine potential synergistic activity. The results indicate that small peptides can act synergistically with TBZ against TBZ-resistant F. sambucinum.
ABSTRACT
Phytopathogenic strains of Burkholderia cepacia (synonym Pseudomonas cepacia) produce endopolygalacturonase, whereas strains of clinical and soil origin do not. Growth of a phytopathogenic strain (ATCC25416) at elevated temperatures resulted in nonpectolytic derivatives that were either cured of a resident plasmid or contained a plasmid of reduced mass. The resident 200-kb plasmid (pPEC320) in strain ATCC25416 was tagged with Tn5-Mob. The pPEC320::Tn5-Mob (pPEC321) plasmid was mobilized in B. cepacia strains of soil and clinical origin. Transconjugants containing pPEC321 expressed the endopolygalacturonase and showed differential activity on plant tissue. No evidence for self-transfer of pPEC320 or the tagged derivative was observed. A 285-kb cloned fragment from pPEC320 containing the plasmid-borne pehA gene was sequenced and compared to the pehA gene from Erwinia carotovora subsp. carotovora and Ralstonia solanacearum and the polygalacturonase sequence from Lycopersicon esculentum.
