a Department of Biosciences , College of Science, Swansea University , Swansea , United Kingdom.
b Department of Biology, Faculty of Science , Tabuk University , Tabuk , Kingdom of Saudi Arabia.
Virulence. 2018;9(1):1449-1467. doi: 10.1080/21505594.2018.1509665.
Entomopathogenic fungi are potential biological control agents of mosquitoes. Our group observed that not all mosquitoes were equally susceptible to fungal infection and observed significant differences in virulence of different spore types. Conidiospores and blastospores were tested against Culex quinquefasciatus larvae. Blastospores are normally considered more virulent than conidia as they form germ tubes and penetrate the host integument more rapidly than conidia. However, when tested against Cx. quinquefasciatus, blastospores were less virulent than conidia. This host-fungus interaction was studied by optical, electron and atomic force microscopy (AFM). Furthermore, host immune responses and specific gene expression were investigated. Metarhizium brunneum (formerly M. anisopliae) ARSEF 4556 blastospores did not readily adhere to Culex larval integument and the main route of infection was through the gut. Adhesion forces between blastospores and Culex cuticle were significantly lower than for other insects. Larvae challenged with blastospores showed enhanced immune responses, with increased levels of phenoloxidase, glutathione-S-transferase, esterase, superoxide dismutase and lipid peroxidase activity. Interestingly, M. brunneum pathogenicity/stress-related genes were all down-regulated in blastospores exposed to Culex. Conversely, when conidia were exposed to Culex, the pathogenicity genes involved in adhesion or cuticle degradation were up-regulated. Delayed host mortality following blastospore infection of Culex was probably due to lower adhesion rates of blastospores to the cuticle and enhanced host immune responses deployed to counter infection. The results here show that subtle differences in host-pathogen interactions can be responsible for significant changes in virulence when comparing mosquito species, having important consequences for biological control strategies and the understanding of pathogenicity processes.
昆虫病原真菌是蚊子的潜在生物防治剂。我们小组观察到并非所有蚊子对真菌感染的敏感性都相同，并观察到不同孢子类型的毒力存在显著差异。我们测试了分生孢子和芽生孢子对库蚊幼虫的作用。芽生孢子通常被认为比分生孢子更具毒性，因为它们形成芽管并比分生孢子更快地穿透宿主表皮。然而，当测试针对库蚊时，芽生孢子的毒性却低于分生孢子。通过光学、电子和原子力显微镜（AFM）研究了这种宿主-真菌相互作用。此外，还研究了宿主免疫反应和特定基因表达。玫烟色棒束孢（原枝孢属anisopliae）ARSEF 4556 芽生孢子不易附着在库蚊幼虫表皮上，主要感染途径是通过肠道。芽生孢子与库蚊表皮之间的粘附力明显低于其他昆虫。用芽生孢子挑战的幼虫表现出增强的免疫反应，酚氧化酶、谷胱甘肽-S-转移酶、酯酶、超氧化物歧化酶和脂质过氧化物酶活性增加。有趣的是，暴露在库蚊中的芽生孢子中，与致病性/应激相关的玫烟色棒束孢基因全部下调。相反，当分生孢子暴露在库蚊中时，参与粘附或表皮降解的致病性基因上调。芽生孢感染库蚊后宿主死亡率延迟可能是由于芽生孢子与表皮的粘附率较低以及宿主为抵御感染而增强的免疫反应所致。这里的结果表明，在比较蚊子物种时，宿主-病原体相互作用的细微差异可能导致毒力发生重大变化，这对生物防治策略和对致病性过程的理解具有重要意义。
