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competing interests. Authors’ contributions GSL designed and performed most of the experiments, analyzed data and wrote the manuscript. STH designed, supervised all the experiments, analyzed data and wrote the manuscript. KFC provided ColE7 for colicin assay and gave suggestions. PHL provided the antibodies against BtuB, TolQ, TolR, TolA, TolB, Pal, and OmpF for this research. WJS and WSH gave suggestions and analyzed data for this research. All the authors have read and approved the final manuscript.”
“Background Metarhizium acridum is a haploid entomopathogenic
fungus (Hypocreales: Clavicipitaceae). M. acridum isolates have been used as biocontrol agents for crop pests, including sugar cane grubs, termites, cockroaches, and rhinoceros much beetles [1]. M. acridum was commercialized and used for locust control in Australia, West Africa [2], and China [3]. Insecticide resistance, pest resurgence, and concerns over environmental impact have made the search for alternative means of biological pest control more urgent. Unfortunately, large-scale use of fungal biocontrol agents is partially limited by the failure of conidia to retain virulence during long-term storage, transportation, and use under stressful conditions, such as high temperature, low humidity, and sunlight exposure [4–6]. Manipulation of culture conditions could optimize the concentration of spore polyols and sugars, including trehalose, and consequently increase tolerance to low relative humidity [7, 8]. However, genetic manipulations of these polyols and sugars to enhance environmental tolerance have not been explored in entomopathogenic fungi. To genetically engineer more robust entomopathogenic fungi, we focused on the trehalose pathways involved in stress response. Trehalose is a storage carbohydrate as trehalose concentrations are high when nutrients are limited in resting cells.