Diverse bacterial symbionts of insect-pathogentic fungi and possible impact on the maintenance of virulence during infection

Abstract

Bacterial-fungal interactions (BFIs) which have important ramifications for the biology of the interacting partners have been demonstrated extensively. Here we show for the first time that diverse bacterial symbionts occur in insect-pathogenic fungi. We firstly detected the bacterial symbionts by fluorescence in situ hybridization in combination with confocal laser scanning microscopy in Pandora neoaphidis. We also compared P. neoaphidis with the closely related species, P. nouryi, and found that 26 OTUs of bacterial symbionts covered taxonomically six classes in bacterial lineage, most were member of Gammaproteobacteria. To make inferences about the vertical transmission of bacterial symbionts, we compared their diversity in the hyphae and primary conidia of one isolate. Nine OTUs were identified and classified into four classes. Although the frequency of class Gammaproteobacteria was higher than other classes, the Shannon-Weiner diversity index was similar. Additionally, to understand the relationship between fungal virulence and bacterial symbiont diversity within fungi, we compared the predictive 16s rRNA clone library and the virulence of two genetically comparable isolates with different diversities of symbionts (F98028+ and F98028−). Conclusively, our study revealed the diversity of potential bacterial symbionts found inside insect-fungal structures through 16s rRNA clone library construction, and the potential impact between P. neoaphidis virulence and diversity in the bacterial symbionts harbored within their hyphae and conidia.