Odhiambo Benard Omondi, Xu Gaoge, Qian Guoliang, Liu Fengquan
College of Plant Protection Nanjing Agricultural University, Nanjing, 210095, China.
Curr Microbiol. 2017 Apr;74(4):437-448. doi: 10.1007/s00284-017-1206-1. Epub 2017 Feb 17.
Lysobacter enzymogenes OH11 produces heat-stable antifungal factor (HSAF) and lytic enzymes possessing antifungal activity. This study bio-prospected for other potential antifungal factors besides those above. The cells and extracellular metabolites of L. enzymogenes OH11 and the mutants ΔchiA, ΔchiB, ΔchiC, Δclp, Δpks, and ΔpilA were examined for antifungal activity against Fusarium graminearum PH1, the causal agent of Fusarium head blight (FHB). Results evidenced that OH11 produces an unidentified extracellular heat-stable degrading metabolite (HSDM) that exhibit degrading activity on F. graminearum PH1 chitinous hyphae. Interestingly, both heat-treated and non-heat-treated extracellular metabolites of OH11 mutants exhibited hyphae-degrading activity against F. graminearum PH1. Enzyme activity detection of heat-treated metabolites ruled out the possibility of enzyme degradation activity. Remarkably, the PKS-NRPS-deficient mutant Δpks cannot produce HSAF or analogues, yet its metabolites exhibited hyphae-degrading activity. HPLC analysis confirmed no HSAF production by Δpks. Δclp lacks hyphae-degrading ability. Therefore, clp regulates HSDM and extracellular lytic enzymes production in L. enzymogenes OH11. ΔpilA had impaired surface cell motility and significantly reduced antagonistic properties. ΔchiA, ΔchiB, and ΔchiC retained hyphae-degrading ability, despite having reduced abilities to produce chitinase enzymes. Ultimately, L. enzymogenes OH11 can produce other unidentified HSDM independent of the PKS-NRPS genes. This suggests HSAF and lytic enzymes production are a fraction of the antifungal mechanisms in OH11. Characterization of HSDM, determination of its biosynthetic gene cluster and understanding its mode of action will provide new leads in the search for effective drugs for FHB management.
食纤维菌属产酶菌株OH11可产生热稳定抗真菌因子（HSAF）和具有抗真菌活性的裂解酶。本研究对除上述因子之外的其他潜在抗真菌因子进行了生物勘探。研究检测了食纤维菌属产酶菌株OH11及其突变体ΔchiA、ΔchiB、ΔchiC、Δclp、Δpks和ΔpilA的细胞及细胞外代谢产物对禾谷镰刀菌PH1（小麦赤霉病的病原菌）的抗真菌活性。结果表明，OH11产生一种未知的细胞外热稳定降解代谢产物（HSDM），该产物对禾谷镰刀菌PH1的几丁质菌丝具有降解活性。有趣的是，OH11突变体的热处理和未热处理细胞外代谢产物均对禾谷镰刀菌PH1表现出菌丝降解活性。对热处理代谢产物的酶活性检测排除了酶降解活性的可能性。值得注意的是，缺乏聚酮合酶-非核糖体肽合成酶的突变体Δpks不能产生HSAF或其类似物，但其代谢产物仍表现出菌丝降解活性。高效液相色谱分析证实Δpks不产生HSAF。Δclp缺乏菌丝降解能力。因此，clp调控食纤维菌属产酶菌株OH11中HSDM和细胞外裂解酶的产生。ΔpilA的表面细胞运动能力受损，拮抗特性显著降低。ΔchiA、ΔchiB和ΔchiC尽管产生几丁质酶的能力有所下降，但仍保留菌丝降解能力。最终，食纤维菌属产酶菌株OH11可独立于聚酮合酶-非核糖体肽合成酶基因产生其他未知的HSDM。这表明HSAF和裂解酶的产生只是OH11抗真菌机制的一部分。对HSDM的特性鉴定、其生物合成基因簇的确定及其作用方式的了解将为寻找防治小麦赤霉病的有效药物提供新线索。
