Comparative genomics of virulence towards malaria mosquitoes in Beauveria bassiana

Entomopathogenic fungi such as Metarhizium anisopliae and Beauveria bassiana have been proposed as biological control agents to kill malaria mosquitoes. Indeed, it has been shown that these fungi successfully reduce the lifespan of mosquitoes in the laboratory and in the field. Previously, we characterized the natural variation in virulence of 29 isolates of Beauveria bassiana and showed that there were up to 10-fold differences in virulence between the most virulent isolate compared to the least virulent isolate. This natural variation can be used to uncover the genetic mechanisms underpinning virulence, which will provide essential information for (i) further improving fungi as biocontrol agents, and (ii) estimating the likelihood of resistance development in the vector, i.e. mosquitoes. In this study, we sequenced 5 isolates representing the extremes of low/high virulence for further comparative genomic analysis. The genomes were de novo assembled and the draft genome size varied from 35.02 Mb to 38.83 Mb. The predicted encoding proteins were supported with three RNA-Seq libraries, and ranged from 10,283 to 10,831 genes. The core set consisted of 8800 genes shared between all isolates. We focused on the genome differences between isolates with contrasting virulence, with special emphasis on gene gain/loss, single nucleotide polymorphisms (SNPs), and secreted proteins. Our findings are discussed in the context of other sequenced entomopathogenic fungi (Metarhizium anisopliae, M. robertsii and M. acridum) as well as plant pathogenic fungi.