Production of Diverse Beauveriolide Analogs in Closely Related Fungi: a Rare Case of Fungal Chemodiversity

Abstract

Fungal chemodiversity is well known in part due to the production of diverse analogous compounds by a single biosynthetic gene cluster (BGC). Usually, similar or the same metabolites are produced by closely related fungal species under a given condition, the foundation of fungal chemotaxonomy. Here, we report a rare case of the production of the cyclodepsipeptide beauveriolides (BVDs) in three insect-pathogenic fungi. We found that the more closely related fungi Beauveria bassiana and Beauveria brongniartii produced structurally distinct analogs of BVDs, whereas the less-close relatives B. brongniartii and Cordyceps militaris biosynthesized structurally similar congeners under the same growth condition. It was verified that a conserved BGC containing four genes is responsible for BVD biosynthesis in three fungi, including a polyketide synthase (PKS) for the production of 3-hydroxy fatty acids (FAs) with chain length variations. In contrast to BVD production patterns, phylogenetic analysis of the BGC enzymes or enzyme domains largely resulted in the congruence relationship with fungal speciation. Feeding assays demonstrated that an FA with a chain length of eight carbon atoms was preferentially utilized, whereas an FA with a chain longer than 10 carbon atoms could not be used as a substrate for BVD biosynthesis. Insect survival assays suggested that the contribution of BVDs to fungal virulence might be associated with the susceptibility of insect species. The results of this study enrich the knowledge of fungal secondary metabolic diversity that can question the reliability of fungal chemotaxonomy. IMPORTANCE Fungal chemotaxonomy is an approach to classify fungi based on the fungal production profile of metabolites, especially the secondary metabolites. We found an atypical example that could question the reliability of fungal chemical classifications in this study, i.e., the more closely related entomopathogenic species Beauveria bassiana and Beauveria brongniartii produced structurally different congeners of the cyclodepsipeptide beauveriolides, whereas the rather divergent species B. brongniartii and Cordyceps militaris biosynthesized similar analogs under the same growth condition. The conserved biosynthetic gene cluster (BGC) containing four genes present in each species is responsible for beauveriolide production. In contrast to the compound formation profiles, the phylogenies of biosynthetic enzymes or enzymatic domains show associations with fungal speciation. Dependent on the insect species, production of beauveriolides may contribute to fungal virulence against the susceptible insect hosts. The findings in this study augment the diversity of fungal secondary metabolisms.

Conservative production of galactosaminogalactan in Metarhizium is responsible for appressorium mucilage production and topical infection of insect hosts

“…1.5 kb upstream of the start codon) using different primers ( S5 Table ). The purified fragments were individually cloned into the vector pDHt-sur (with a sur gene for conferring sulfonylurea resistance) [ 61 ]. The null mutants were then transformed to obtain the drug-resistant colonies, which were further verified by PCR and RT-PCR for successful gene complementation.…”

The Chemical Ecology Approach to Reveal Fungal Metabolites for Arthropod Pest Management

“…The compounds were isolated from B. bassiana , B. tenella (= B. brongneartii ), Cordyceps militaris , and P. fumosoroseus (= Isaria fumosorosea ). Beauverolide A is one of the virulence factors of these EPF [ 52 ]. Beauverolide A at 10 µg per larva showed weak insecticidal activity against the taro caterpillar S. litura (20% mortality) and the Chinese bruchid Callosobruchus chinensis (death of 40% of females) with the absence of antimicrobial activity [ 53 ].…”

“…Numerous metabolites (especially minor ones) of EPF have not been commonly bioassayed on arthropods [ 52 , 90 ] and still awaited the evaluation for anti-insectan activity. Other groups of fungi, phylogenetically related to soil micromycetes and EPF can be used for screening programs.…”

Promising approaches to the search for fungal metabolites for management of arthropod pests

“…Приведенные выше данные свидетельствуют, что наиболее интересной экологической группой грибов для выявления низкомолекулярных соединений с инсектицидными свойствами представляются почвенные микромицеты, в частности, из родов Aspergillus и Penicillium. Однако следует отметить, что инсектицидные метаболиты других почвообитающих грибов, за исключением микотоксинов (Dowd, 2002), еще плохо изучены, например, многочисленные минорные метаболиты ЭПГ (Yin et al, 2020;Zhang et al, 2020). Как малоизученые продуценты низкомолекулярных инсектицидных молекул интерес представляют эндофитные грибы (Gange et al, 2019).…”

“…Еще несколько новых боверолидов удалось выявить при культивировании B. bassiana на живых тканях мозга муравья Camponotus pennsylvanicus и использовании метаболомного подхода к изучению экстрактов из инфицированного грибом биоматериала (de Bekker et al, 2013). В смешанной культуре B. bassiana, эндофита Irpex lacteus и фитопатогена Nigrospora oryzae выявлено 5 новых соединений, однако из 20 выделенных веществ максимальной детеррентной активностью против гусениц шелкопряда обладал тремулендиол A в концентрации 6.25 мкг/см 2 (Yin et al, 2020). Углубленные метаболомные исследования с использованием методов МС/МС и высокоразрешающей масс-спектрометрии позволили выявить новые для Metarhizium spp.…”