Diversity of endo-and exo-bacteria associated with soil fungi

Fungi are cosmopolitan microorganisms with complex genetic make-up and metabolism.[1, 2] Furthermore, this group of microorganisms possesses important roles in ecology, agriculture, forestry and human health. In soil, fungi are one of the most abundant group of microorganisms and are known to interact with different microorganisms, including bacteria. Bacterial:fungal interactions in soils can be positive or negative (synergistic or antagonistic). In the present study, we obtained 45 fungal isolates and 53 exobacteria associated with the fungal isolates from soil microcosms from six different locations. These fungi were obtained with different growth media of plant origin, namely cornmeal, oatmeal, sorghum grain, and potato carrot. The fungal isolates were also investigated via real-time PCR for endobacteria. Out of the 45 fungal isolates, 41 were associated with endobacteria. From this culture collection, four fungal isolates (Didymella spp., Neopestalotiopsis spp., Staphylotrichum coccosporum, Aspergillus spp.) and four bacterial isolates (Exiguobacterium sp., two Paenibacillus spp., and Pseudomonas sp.) associated with these fungi with synergistic and antagonistic interactions from the same microcosm were selected for further investigation. The selection was based on confrontational assays. These confrontational assays allowed us to distinguish bacteria that would inhibit or enhance fungal growth. In addition to the exobacteria interaction with fungi, another five fungi were selected to further investigate for the endo-bacteria association based on the real time PCR results. The fungi selected were Didymella glomerata, Cladosporium sp., Aspergillus fumigatus, Aspergillus sp. and Byssochlamys spectabilis. Hydrophobicity analyses via contact angle and surface composition via Attenuated total reflection Fourier transform infrared (ATR-FTIR) were also employed to better understand the physical interactions of the bacteria with these fungi. All nine fungal isolates presented cell surfaces with moderate to high hydrophobicity. The main functional groups observed on the surface of these fungi belonged to polysaccharides as well as phosphate compounds and proteins. Further investigations of the metabolites involved in the communication between the fungi and the bacteria triggering negative and positive interactions are underway. References [1] L. de Aguirre, S.F. Hurst, J.S. Choi, J.H. Shin, H.P. Hinrikson, C.J. Morrison, Rapid Differentiation of Aspergillus Species from Other Medically Important Opportunistic Molds and Yeasts by PCR-Enzyme Immunoassay, Journal of Clinical Microbiology, 42 (2004) 3495-3504. [2] R.E. McKinney, Environmental pollution control microbiology: a fifty-year perspective, CRC Press, 2004. This study was supported by a U.S. Department of Energy Biological and Environmental Research Science Focus Area grant (grant no. DE-AC52-06NA25396).