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.