Virulence of three Aspergillus species to the model insect Galleria mellonella and the contribution of ergot alkaloids to the pathogenic potential of Aspergillus leporis

Opportunistically pathogenic fungi have varying potential to cause disease
in animals. Factors contributing to their virulence include specialized
metabolites, which is some cases evolved in contexts unrelated to
pathogenesis.  Specialized metabolites that increase fungal
virulence in the model insect Galleria mellonella include the ergot
alkaloids fumigaclavine C in Aspergillus fumigatus (syn. Neosartorya
fumigata) and lysergic acid α-hydroxyethylamide (LAH) in the
entomopathogen Metarhizium brunneum. Three species of Aspergillus
recently found to accumulate high concentrations of LAH were investigated
for their pathogenic potential in G. mellonella.  Aspergillus
leporis was most virulent, A. hancockii was intermediate, and A.
homomorphus had very little pathogenic potential. Aspergillus
leporis and A. hancockii emerged from and sporulated on dead insects, thus
completing their asexual life cycles. Inoculation by injection resulted in
more lethal infections than did topical inoculation,
indicating A. leporis and A. hancockii were pre-adapted for
insect pathogenesis but lacked an effective means to breach the insect’s
cuticle. All three species accumulated LAH in infected insects,
with A. leporis accumulating the most.  Concentrations
of LAH in A. leporis were similar to those observed in the entomopathogen
M. brunneum. LAH was eliminated from A. leporis through a
CRISPR/Cas9-based gene knockout, and the resulting strain had reduced
virulence to G. mellonella. The data indicate A. leporis and A.
hancockii have considerable pathogenic potential and that LAH increases
the virulence of A. leporis.

机会致病性真菌（opportunistically pathogenic fungi）对动物的致病潜力存在显著差异。影响其毒力的因素包括特化代谢产物，这类产物在多数情况下的演化背景与致病过程无关。在模式昆虫大蜡螟（Galleria mellonella）模型中，可增强真菌毒力的特化代谢产物包括：烟曲霉（Aspergillus fumigatus，异名：新萨托菌Neosartorya fumigata）中的麦角生物碱烟曲霉色胺C（fumigaclavine C），以及昆虫病原真菌布氏白僵菌（Metarhizium brunneum）中的麦角酸α-羟乙酰胺（lysergic acid α-hydroxyethylamide，LAH）。研究人员针对近期发现的3种可高浓度积累LAH的曲霉属（Aspergillus）物种，探究了它们在大蜡螟体内的致病潜力：其中兔曲霉（Aspergillus leporis）毒力最强，汉考克曲霉（A. hancockii）毒力中等，同形曲霉（A. homomorphus）几乎无致病潜力。兔曲霉与汉考克曲霉可从死亡昆虫体内萌发并产孢，由此完成其无性生命周期。相较于体表接种，注射接种可引发更为严重的致死性感染，这表明兔曲霉与汉考克曲霉已预先适应昆虫致病过程，但缺乏有效突破昆虫体壁的手段。3种曲霉均可在受感染的昆虫体内积累LAH，其中兔曲霉的LAH积累量最高，其浓度与昆虫病原真菌布氏白僵菌中的水平相当。研究人员通过基于CRISPR/Cas9的基因敲除技术，完全去除了兔曲霉中的LAH合成能力，所得突变菌株对大蜡螟的毒力显著降低。实验数据表明，兔曲霉与汉考克曲霉具备较强的昆虫致病潜力，且LAH可显著增强兔曲霉的毒力。