Different strains of Metarhizium exhibit a range of polymorphisms in colony phenotypes. These phenotypes range from highly conidiating colonies to colonies that produce relatively more mycelia and few conidia. These different phenotypes are exhibited in infected insects in the soil. In this paper, we provide a theoretical consideration of colony polymorphisms and suggest that these phenotypes represent a range of strategies in the soil that Metarhizium exhibits. We call these different strategies “sleepers” and “creepers”. The “sleeper” phenotype produces relatively greater amounts of conidia. We use the term “sleeper” to identify this phenotype since this strategy is to remain in the soil as conidia in a relatively metabolically inactive state until a host insect or plant encounter these conidia. The “creeper” phenotype is predominantly a mycelial phenotype. In this strategy, hyphae move through the soil until a host insect or plant is encountered. We theoretically model the costs and benefits of these phenotypic polymorphisms and suggest how evolution could possibly select for these different strategies.

Beneficial associations are very important for plants and soil-dwelling microorganisms in different ecological niches, where communication by chemical signals is relevant. Among the chemical signals, the release of phytohormones by plants is important to establish beneficial associations with fungi, and a recently described association is that of the entomopathogenic ascomycete fungus Metarhizium with plants. Here, we evaluated the effect of four different phytohormones, synthetic strigolactone (GR24), sorgolactone (SorL), 3-indolacetic acid (IAA) and gibberellic acid (GA₃), on the fungus Metarhizium guizhouense strain HA11-2, where the germination rate and hyphal elongation were determined at three different times. All phytohormones had a positive effect on germination, with GA₃ showing the greatest effect, and for hyphal length, on average, the group treated with synthetic strigolactone GR24 showed greater average hyphal length at 10 h of induction. This work expands the knowledge of the effect of phytohormones on the fungus M. guizhouense, as possible chemical signals for the rapid establishment of the fungus–plant association.

Most organisms are associated with microorganisms, which influence their behavior during their life cycles. Fungi are no exception; they interact with plants, viruses, and bacteria in various environments, forming complex communities. These associations can occur externally around the mycelia and internally within the hyphae. Fungi can harbor bacteria, mycoviruses, and other fungi within their hyphae. Some endobacteria (EB) have been shown to alter fungal host function, development, and interactions with other organisms. Most fungi that host endobacteria (EB) are plant-associated. Although members of the genus Metarhizium are among the most abundant fungi isolated from soils, their associated EB have not been sufficiently studied. Endobacteria were recently detected in M. bibiondarum and M. anisopliae; however, the biological roles of these bacteria in the different Metarhizium life cycles remain unknown. In this study, Metarhizium strains were isolated from the rhizosphere and Phyllophaga spp. Bacillus subtilis was identified as an endobacterium, and its influence on the physiology of Metarhizium and entomopathogenic capacity was studied. Our analysis revealed that EB have a negative impact on the virulence of Metarhizium against Galleria mellonella and Tenebrio molitor.

Most organisms are associated with microorganisms, which influence their behavior during their life cycles. Fungi are no exception; they interact with plants, viruses, and bacteria in various environments, forming complex communities. These associations can occur externally around the mycelia and internally within the hyphae. Fungi can harbor bacteria, mycoviruses, and other fungi within their hyphae. Some endofungal bacteria (EHB) have been shown to alter fungal host function, development, and interactions with other organisms. Most fungi that host EHB are plant-associated. Although members of the genus Metarhizium are among the most abundant fungi isolated from soils, their associated EHB have not been sufficiently studied. Endobacteria were recently detected in M. bibiondarum and M. anisopliae; however, the biological roles of these bacteria in the different Metarhizium life cycles remain unknown. In this study, Metarhizium strains were isolated from the rhizosphere and Phyllophaga spp. Bacillus subtilis was identified as an endobacterium, and its influence on Metarhizium’s physiology and entomopathogenic capacity was studied. Our analysis revealed that EHB have a negative impact on the virulence of Metarhizium against Galleria mellonella and Tenebrio molitor.