| Fungi and bacteria have been ubiquitous neighbors in nearly every imaginable ecological niche for hundreds of millions of years, yet relatively little is known of how these organisms communicate. Historically our understanding of bacterial-fungal interactions (BFIs) are largely limited to antibiosis, especially against pathogens of animals and plants. Recently the tremendous impact of the polymicrobial milieu (i.e. microbiomes) on animal and plant health has been recognized and research has started to emerge regarding community composition and dynamics resulting from both abiotic and biotic interactions. Understanding what the chemical communication signals are and their outcomes in BFIs is essential to moving beyond antibiosis and finding new modes of modulating polymicrobial systems in agriculture, medicine, and industry.;This thesis explores the language of microbial interkingdom communications and its impacts on microbial development, morphology and symbioses. I examined a variety of interaction conditions including: volatile, diffusible, and direct-contact interactions between the bacterial plant pathogen, Ralstonia solanacearum, and plant associated fungi. The outcomes of these interactions impact both R. solanacearum and the fungi they interact with, causing shifts in development, secondary metabolism, dispersal, and endosymbiotic interactions. Specifically, volatile interactions resulted in dramatic reductions in bacterial EPS and melanin production with concomitant reductions in fungal sporulation and increased aflatoxin production, potentially modulated by overlapping volatile profiles. Diffusible and physical interactions between R. solanacearum and many fungi, such as Aspergillus flavus and Fusarium fujikuroi, resulted in fungal chlamydospore development, bacterial endosymbiosis, and dramatic shifts in secondary metabolite regulation; all driven by the bacterial lipopeptide ralsolamycin.;By coupling in vitro coculture methodologies with modern metabolomics and genetic manipulations of bacteria and fungi, this thesis provides a deeper understanding of the chemistry and biology of this intermicrobial communication. While many of the findings are novel, I anticipate that they represent a more common yet undescribed phenomenon of other bacterial-fungal interactions in the soil and on plant surfaces. Further research into the developing field of bacterial-fungal chemical communication will undoubtedly contribute significantly to both basic and applied fields of microbial ecology, agriculture, and medicine. |
