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An antifungal secondary metabolite from Lysobacter enzymogenes strain C3: Isolation, biological activity, mode of action and potential use in plant disease control
Lysobacter enzymogenes strain C3 is a biological control agent against fungal pathogens. Its activity was attributed previously to multiple antifungal lytic enzymes. In this study, a heat stable antibiotic (HSAF) was also found to be responsible for antifungal activity in vitro. HSAF was extracted from C3 culture fluid by ammonium sulfate precipitation and solubilization in methanol and was further isolated by TLC and HPLC. The purified antibiotic was active against a wide range of fungal and oomycete species but not against Saccharomyces cerevisiae or bacteria. It inhibited spore germination and disrupted hyphal polarity in vitro. These effects also were observed when HSAF was applied to tall fescue leaves. In addition, it inhibited appressorium formation and suppressed leaf spot development by Bipolaris sorokiniana. Aspergillus nidulans was used as a model to investigate its mode of action. barA and basA mutants were identified that were resistant and hypersensitive to HSAF respectively. Supplementation experiments suggest HSAF targets BarA-dependent ceramide synthesis, whereas a second ceramide synthase, LagA, is not a likely target for HSAF. HSAF also induced abnormal cell wall thickening at hyphal tips and septa in A. nidulans. β-1,3-glucan was accumulated in thickened area while there was an apparent reduction in chitin levels. A similar pattern of cell wall deposition was observed in mutants in which synthesis of ceramide or phytosphingosine are impaired. In addition, exogenous supplementation of dihydrosphingosine and phytosphingosine mimicked HSAF effects. Supplementation with phytoceramide reversed some of the effects of HSAF, restoring hyphal polarity but having no effects on HSAF-induced cell wall thickening. These results suggest that HSAF-induced depletion of ceramide is involved in disruption of hyphal polarity, while accumulation of sphingoid bases rather than depletion of ceramide is the cause of HSAF-induced cell wall thickening. ^
Li, Shaojie, "An antifungal secondary metabolite from Lysobacter enzymogenes strain C3: Isolation, biological activity, mode of action and potential use in plant disease control" (2005). ETD collection for University of Nebraska - Lincoln. AAI3186864.