Genome analysis and hyphal movement characterization of the hitchhiker endohyphal Enterobacter sp. from Rhizoctonia solani

Abstract

Bacterial-fungal interactions are pervasive in the rhizosphere. While an increasing number of endohyphal bacteria (EHB) have been identified, little is known about their ecology and impact on the associated fungal hosts and the surrounding environment. In this study, we characterized the genome of an Enterobacter sp. (En-Cren) isolated from the generalist fungal pathogen Rhizoctonia solani. Overall, the En-Cren genome size was typical for members of the genus and was capable of free-living growth. The genome was 4.6 MB in size, and no plasmids were detected. Several prophage regions and genomic islands were identified that harbor unique genes in comparison with phylogenetically closely related Enterobacter spp. Type VI secretion system and cyanate assimilation genes were identified from the bacterium, while common heavy metal resistance genes were absent. En-Cren contains the key genes for indole-3-acetic acid (IAA) and phenylacetic acid (PAA) biosynthesis, and produces IAA and PAA in vitro, which may impact the ecology or pathogenicity of the fungal pathogen in vivo. En-Cren was observed to move along hyphae of R. solani and on other basidiomycetes and ascomycetes in culture. The bacterial flagellum is essential for hyphal movement, while other pathways and genes may also be involved. ImportanceThe genome characterization and comparative genomics analysis of En-Cren provided the foundation and resources for a better understanding of the ecology and evolution of this EHB in the rhizosphere. The ability to produce IAA and PAA may provide new angles to study the impact of phytohormones during the plant-pathogen interactions. The hitchhiking behavior of the bacterium on a diverse group of fungi, while inhibiting the growth of some others, revealed new areas of bacterial-fungal signaling and interaction yet to be explored.