Donald M. Walker – I am an Associate Professor in the Department of Biology at Middle Tennessee State University. I received my Ph.D. from Rutgers University in 2012. I conducted doctoral research on the systematics, ecology and evolutionary biology of plant pathogenic fungi in the Gnomoniaceae (Diaporthales) under the advisors Amy Rossman and Lisa Castlebury at the Systematic Mycology Lab and James White at Rutgers University. My research expertise lies in the areas of molecular evolution and ecology of microorganisms with an emphasis on fungi. Past research projects have focused on the evolution of fungal pathogens and utilized systematics, phylogenetics, and molecular marker development to integrate evolutionary biology and host-fungal interactions. More recently my lab group has studied host-microbiome-pathogen associations in reptile and amphibian (herptile) species. Emerging infectious fungal pathogens are threatening wildlife world-wide, and the Southeast United States is a global ‘hotspot’ for biodiversity, so serves as a foundation for our field studies.

The tissues and organs of multicellular organisms are colonized by microbial assemblages, commonly referred to as the host microbiome, which are distinct from the surrounding environment. The microbiome acts as an important line of defense against fungal pathogenicity and its composition can be altered by factors such as microtopography, host life history, and environmental heterogeneity. I have focused my career on understanding the interactions between wildlife hosts, their skin and gut microbiomes, and emerging infectious fungal pathogens and their implications for disease ecology and biodiversity conservation. Emerging infectious fungal diseases are known to reduce animal population sizes, cause extirpation/extinction events, and have indirect adverse consequences on human well-being. I have established two central study systems in my lab focused on pathogen induced dysbiosis (PID) and bacterial-fungal interactions (BFIs). We plan to disentangle mechanisms of microbial assembly in host-microbiome-pathogen systems and determine the potential for microbiomes to be used in bioaugmentation programs and biodiversity conservation. Most notably, my study systems span three major ecological scales including field, live animal timeseries and controlled microbial enrichment experiments to understand the drivers of community assembly resulting from PID and BFIs.

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2024

(47) Romer, A.S., Grisnik, M., Dallas, J.W., Sutton, W., Murray, C.M., Hardman, R.H., Blanchard, T., Hanscom, R.J., Clark, R.W., Godwin, C., Alexander, N.R., Moe, K.C., Cobb, V.A., Eaker, J., Colvin, R., Thames, D., Ogle, C., Campbell, J., Frost, C., Brubaker, R.L., Snyder, S.D., Rurik, A.J., Cummins, C.E., Ludwig, D.W., Phillips, J.L., Walker, D.M. 2024. Effects of snake fungal disease (ophidiomycosis) on the skin microbiome across two major experimental scales. Conservation Biology. https://doi.org/10.1111/cobi.14411

(46) Vargas-Gastélum, L., Romer, A.S., Ghotbi, M., Dallas, J.W., Alexander, N.R., Moe, K.C., McPhail, K.L., Neuhaus, G.F., Shadmani, L., Spatafora, J.W., Stajich, J.E., Tabima, J.F., Walker, D.M. Herptile gut microbiomes: a natural system to study multi-kingdom interactions between filamentous fungi and bacteria. Msphere. 2024 Mar 26;9(3):e00475-23. https://doi.org/10.1128/msphere.00475-23

2022

(45) Hill, A. J., Grisnik, M. and Walker, D. M. 2022. Bacterial Skin Assemblages of Sympatric Salamanders are Primarily Shaped by Host Genus. Microbial Ecology. https://doi.org/10.1007/s00248-022-02127-0

(44) Grisnik, M., Grinath, J.B., Munafo, J.P., Walker, D.M. 2022. Functional Redundancy in Bat Microbial Assemblage in the Presence of the White Nose Pathogen. Microbial Ecology. https://doi.org/10.1007/s00248-022-02098-2

(43) Graham, S.P., Walker, D.M., Kelehear, C., Jensen, J.B., Dunn, K., Guyer, C. 2022. Georgia Distribution and Characterization of Species within the Eurycea quadridigitata Complex. Southeastern Naturalist. https://doi.org/10.1656/058.021.0207

(42) Romer, A.S., Grinath, J.B., Moe, K.C., Walker, D.M. 2022. Host microbiome responses to the Snake Fungal Disease pathogen (Ophidiomyces ophidiicola) are driven by changes in microbial richness. Scientific Reports. https://doi.org/10.1038/s41598-022-07042-5​

2021

(41) Godwin, C.D., Walker, D.M., Romer, A.S., Grajal-Puche, A., Grisnik, M., Goessling, J.M., Perkin, J.S., Murray, C.M. 2021. Testing the febrile response of snakes inoculated with Ophidiomyces ophidiicola, the causative agent of snake fungal disease. Journal of Thermal Biology. https://doi.org/10.1016/j.jtherbio.2021.103065

(40) Grisnik, M., Grinath, J.B., Walker, D.M. 2021. The presence of Pseudogymnoascus destructans, a fungal pathogen of bats, correlates with changes in microbial metacommunity structure. Scientific Reports. https://doi.org/10.1038/s41598-021-91118-1

(39) Perkin, J.S., Papraniku, I.F., Gibbs, W.K., Hoeinghaus, D.J., Walker, D.M. 2021. Temporal trajectories in metacommunity structure: Insights from interdisciplinary research in intermittent streams. WIREs Water. https://doi.org/10.1002/wat2.1531

(38)  Hill, A.J., Hardman, R.H., Sutton, W.B., Grisnik, M.S., Gunderson, J.H., Walker, D.M. 2021. Absence of Batrachochytrium salamandrivorans in a Global Hotspot for Salamander Biodiversity. Journal of Wildlife Diseases. https://doi.org/10.7589/JWD-D-20-00218

(37) Romer, A.S., West, J., Phipps, E., Moe, K., Walker, D.M. 2021. Nerodia sipedon (Northern Water Snake) shedding. The Tennessee Journal of Herpetology. 4: 24-26.

2020

(36) Chapagain, P., Walker D.M., Leeds, T., Cleveland, B.M., Salem, M. 2020. Distinct microbial assemblages associated with genetic selection for high-and low-muscle yield in rainbow trout. BMC genomics. https://doi.org/10.1186/s12864-020-07204-7

(35) Grajal-Puche, A., Murray, C.M., Kearley, M., Merchant, M., Nix, C., Warner, J.K., Walker, D.M. 2020. Microbial assemblage dynamics within the American Alligator nesting ecosystem: A comparative approach across ecological scales. Microbial Ecology. https://doi.org/10.1007/s00248-020-01522-9

(34) Snyder, S.D., Sutton, W.B., Walker, D.M. 2020. Prevalence of Ophidiomyces ophiodiicola, the causative agent of snake fungal disease, in the interior plateau ecoregion of Tennessee, USA. Journal of Wildlife Diseases. https://doi.org/10.7589/2019-04-109

(33) Grisnik, M., Bowers, O., Moore, A.J., Jones, B.F., Campbell, J.R., Walker, D.M. 2020. The cutaneous microbiota of bats has in vitro antifungal activity against the white nose pathogen. FEMS Microbiology Ecology. doi: 10.1093/femsec/fiz193

(32) Walker, D.M., Hill, A.J., Albecker, M.A., McCoy, M.W., Grisnik, M., Romer, A., Grajal-Puche, A., Camp, C., Kelehear, C., Wooten, J., Rheubert, J., Graham, S.P.  2020. Variation in the Slimy Salamander (Plethodon spp.) Skin and Gut-Microbial Assemblages Is Explained by Geographic Distance and Host Affinity. Microbial Ecology.  https://doi.org/10.1007/s00248-019-01456-x

2019

(31) Chapagain, P., Arivett, B., Cleveland, B.M., Walker, D.M., Salem, M. 2019. Analysis of the fecal microbiota of fast-and slow-growing rainbow trout (Oncorhynchus mykiss). BMC genomics. https://doi.org/10.1186/s12864-019-6175-2

(30) Walker, D.M., Leys, J.E., Grisnik, M., Grajal-Puche, A., Murray, C.M., Allender, M.C. 2019. Variability in snake skin microbial assemblages across spatial scales and disease states. ISME Nature. https://doi.org/10.1038/s41396-019-0416-x

(29) Maynard, D.S., Bradford, M.A., Covey, K.R., Lindner, D., Glaeser, J., Talbert, D.A., Walker, D.M., Crowther, T.W. 2019. Consistent trade-offs in fungal trait expression across broad spatial scales. Nature Microbiology.  https://doi.org/10.1038/s41564-019-0361-5

(28) Minoshima, A., Walker, D.M., Takemoto, S., Hosoya, T., Walker, A.K., Ishikawa, S., Hirooka, Y. 2019. Pathogenicity and taxonomy of Tenuignomonia styracis gen. et sp. nov., a new monotypic genus of Gnomoniaceae on Styrax obassia in Japan. Mycoscience. https://doi.org/10.1016/j.myc.2018.08.001  

2018

(27) Grisnik, M., Leys, J.E., Bryan, D., Hardman, R.H., Miller, D.L., Cobb, V.A., Ogle, C., Simpson, C., Campbell, J.R., Appelgate, R.D., Allender, M.C., Nordberg, E.J., Hoekstra, A.A., Walker, D.M. 2018. Host and geographic range of snake fungal disease in Tennessee, USA. Herpetological Reviews. 49: 682-690.

(26) Walker, D.M., Murray, C.M., Talbert, D., Tinker, P., Graham, S.P., Crowther, T.A. 2018. A salamander's top down effect on fungal communities in a detritivore ecosystem. FEMS Microbiology Ecology. https://doi.org/10.1093/femsec/fiy168

(25) Malone, E.W., Perkin, J.S., Leckie, B.M., Kulp, M.A., Hurt, C.R., Walker, D.M. 2018. Which species, how many, and from where: Integrating habitat suitability, population genomics, and abundance estimates into species reintroduction planning. Global Change Biology.  doi.org/10.1111/gcb.14126

(24) Hayes, D.H., Grisnik, M., Stone, S.A., Tarter, Z.W., Ritter, K., Yanckello, L.M., Oatman, L.E., Myers, L.E., Pellegrino, C.C., Camp, C.D., Walker, D.M., Wooten, J.A. 2018. The culturable skin microbiome of the Ocoee Salamander, Desmognathus ocoee. Tennessee Journal of Herpetology 1: 4–10.  

(23) Tanguay, P., Blais, M., Potvin, A., Stewart, D., Walker, D.M., Nadeau-Thibodeau, N., DesRochers, P., Rioux, D. 2018. qPCR quantification of Ophiognomonia clavigignenti-juglandacearum from infected butternut trees under different release treatments. Forest Pathology. https://doi.org/10.1111/efp.12418

(22) Hill, A., Leys, J.E., Bryan, D., Erdman, F.M., Malone, K.S., Russell, G.N., Applegate, R.D., Fenton, H., Niedringhaus, K., Miller, A.N., Allender, M., Walker, D.M. 2018. Common cutaneous bacteria isolated from snakes inhibit growth of Ophidiomyces ophiodiicola. EcoHealth. doi: 10.1007/s10393-017-1289-y.

2017  

(21) Walker, D.M., Smouse, P.E., Reginato, M., Struwe, L. 2017. Cladal divergence in fungal Ophiognomonia (Gnomoniaceae, Diaporthales) shows evidence of climatic niche vicariance. Biological Journal of the Linnean Society. doi.org/10.1093/biolinnean/blx043

(20) Walker, D.M., Leys, J.E., *Dunham, K.E., Oliver, J., Schiller, E.E., Stephenson, K., Kimrey, J., Wooten, J., Rogers, M.W. 2017. Methodological considerations for detection of terrestrial small-body salamander eDNA and implications for biodiversity conservation. Molecular Ecology Resources. DOI: 10.1111/1755-0998.12667

(19) Talbert, D., Tinker, P., Crowther, T., Walker, D.M. 2017. Using machine learning to understand top-down effects in an ecosystem: opportunities, challenges, and lessons learned. Association for the Advancement of Artificial Intelligence.  

2016  

(18) Hibbett, D., Abarenkov, K., Chai, B., Crous, P., Helgason, T., Herr, J.R., Lueschow, S., O’Donnell, K., Nilsson, R.H., Oono, R., Schoch, C., Smyth, C., Walker, D.M., Andrea, P-A., Taylor, J.W., Geiser, D.M. 2016. Sequence based classification and identification of fungi. Mycologia 108: 16–30.

(17) Shetty, K.G., Rivadeneira, D.V., Jayachandran, K., Walker, D.M. 2016. Isolation and molecular characterization of the fungal endophytic microbiome from conventionally and organically grown avocado trees in South Florida. Mycological Progress. doi:10.1007/s11557-016-1219-3  

2015  

(16) Shuttleworth, L.A., Walker, D.M., Liew, E.C.Y., Guest, D.I. 2015. The chestnut (Castanea spp.) pathogen Gnomoniopsis smithogilvyi (Gnomoniaceae, Diaporthales) and its synonyms. Mycotaxon 130: 929–940.

(15) Walker, D.M., Lawrence, B.R., Esterline, D., McAndrew, M., Edelbrock, J., Graham, S.P., Kelehear, C. 2015. A novel protocol for removing environmental microbes from amphibian skin. Herpetological Reviews 46: 349–353.

(14) Rossman, A.Y., Adams, G.C., Cannon, P.F., Castlebury, L.A., Crous, P.W., Gryzenhout, M., Jaklitsch, W.M., Mejia, L.C., Stoykov, D., Udayanga, D., Voglmayr, H., Walker, D.M. 2015. Recommendations of generic names in Diaporthales competing for protection or use. IMA Fungus DOI: 10.5598/imafungus.2015.06.01.09

(13) Combs, J., Grisnik, M., Baldauf, K., Sigg, M., Swanson, T., Amos, R., White, C.M., Schwaner, T.D., Walker, D.M., Wooten, J.A. 2015. A report of ranavirus infecting midland painted turtles with novel localities for frog infection in northwest Ohio. Herpetological Reviews 46: 361–363.

(12) Nilsson, R.H., Tedersoo, L., Ryberg, M., Kristiansson, E., Hartmann, M., Unterseher, M., Porter,T.M., Bengtsson-Palme, J., Walker, D.M., de Sousa, F., Gamper, H.A., Larsson, E., Larsson, K-H., Kõljalg, U., Edgar, R., Abarenkov, K. 2015. A comprehensive, automatically updated fungal ITS sequence dataset for reference-based chimera control in environmental sequencing efforts. Microbes & Environments DOI:10.1264/jsme2.ME14121  

2014

(11) Walker, D.M., Lawrence, B.R., Esterline, D., Graham, S.P., Edelbrock, M.A., Wooten, J.A. 2014. A metagenomics-based approach to the top-down effect on the detritivore food web; a salamander’s influence on fungal communities within a deciduous forest. Ecology and Evolution DOI: 10.1002/ece3.1259

(10) Schoch, C.L., Robbertse, B., Walker, D.M., and 96 others. 2014. Finding needles in haystacks: linking scientific names, reference specimens and molecular data for Fungi. DATABASE DOI: 10.1093/database/bau061

(9) Walker, A., Hirooka, Y., Walker, D.M. 2014. Ophiognomonia acadiensis. Persoonia 32, 290.

(8) Walker, D.M., Lawrence, B.R., Castlebury, L.A., Rossman, A.Y. 2014. Five new species of the highly diverse genus Plagiostoma (Gnomoniaceae, Diaporthales) from Japan. Mycological Progress DOI: 10.1007/s11557-014-0993-z

(7) Walker, D.M., Castlebury, L.A., Rossman, A.Y., Struwe, L. 2014. Host conservatism or host specialization? Patterns of fungal diversification are influenced by host specificity in Ophiognomonia (Gnomoniaceae, Diaporthales). Biological Journal of the Linnean Society 111, 1–16. DOI: 10.1111/bij.12189  

2013  

(6) Wooten, J.A., Camp, C.D., Combs, J.R., Dulka, E., Reist, A., Walker, D.M. 2013. Re-evaluating niche conservatism versus divergence in the woodland salamander genus Plethodon Tschudi 1838: a case study of the parapatric members of the Plethodon glutinosus (Green 1818) species complex. Canadian Journal of Zoology 91, 883–892. DOI: 10.1139/cjz-2013-0097  

2012  

(5) Walker, D.M., Rossman, A.Y., Adams, G.C., Longa, C.M.O., Maresi, G. 2012. Valsalnicola oxystoma. Persoonia 29, 148.

(4) Walker, D.M., Castlebury, L.A., Rossman, A.Y., Mejía, L.C., White, J.F. 2012. Phylogeny and taxonomy of Ophiognomonia (Gnomoniaceae, Diaporthales), including twenty-five new species in this highly diverse genus. Fungal Diversity 57, 85–147.

(3) Walker, D.M., Castlebury, L.A., Rossman, A.Y., White, J.F. 2012. New molecular markers for fungal phylogenetics: Two genes for species-level systematics in the Sordariomycetes (Ascomycota). Molecular Phylogenetics and Evolution 64, 500–512.

(2) Rossman, A.Y., Melgar, J.C., Walker, D.M., Gonzales, A., Ramirez, T., Rivera, J.M. 2012. First report of Dolabra nepheliae causing stem canker of rambutan and pulasan in Honduras. Plant Disease 96, 765.  

2010  

(1) Walker, D.M., Castlebury, L.A., Rossman, A.Y., Sogonov, M.V., White, J.F. 2010. Systematics of genus Gnomoniopsis (Gnomoniaceae, Diaporthales) based on a three-gene phylogeny, host associations and morphology. Mycologia 102, 1479–1496.

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2023   National Science Foundation. Fungal pathogen induced dysbiosis alters microbiome assembly along host resource gradients: implications for biodiversity conservation. Lead PI. $1M.

2021   National Science Foundation. Gut-inhabiting fungi influence structure and function of herptile microbiomes through horizontal gene transfer and novel metabolic function. Lead PI on collaborative project. $2.61M, $870,000 to MTSU

2019   The Nature Conservancy. Characterization of the endosymbiotic bacterial community of the causative agent of White Nose Syndrome, Pseudogymnoascus destructans, of bats. Lead PI, $35,000.

2019   US Fish and Wildlife Service. Microbiome characterization of endangered darter egg clutches in the Copper Creek drainage. Lead PI, $50,000. 

2018   Natural Resources Conservation Service. Assessing the Restoration Success of WRP Easements in the Lower Mississippi River Valley. Co-PI with Dr. Justin Murdock. Total award: $1,650,016. MTSU subaward to conduct microbiome work: $257,649

2018   US Fish and Wildlife Service, State Wildlife Grant. Understanding the impact of snake fungal disease on species of greatest conservation need in Tennessee. Lead PI, $109,000.

2017  US Fish and Wildlife Service, State Wildlife Grant. The probiotic microbiome of endangered Tennessee bats: implications for biodiversity conservation and development of WNS biocontrol agents. Lead PI, $81,000.

2016  US Fish and Wildlife Service, State Wildlife Grant. The origin, host, and geographic range of snake fungal disease with an emphasis on species of greatest conservation need in Tennessee. Lead PI, $7,700.

2016  Great Smoky Mountains Conservation Association Campbell Fellowship. Keystone community members in the microbiome of salamander skin affect pathogenicity of chytrid fungi (Batrachochytrium spp.). Co-PI with Aubree Hill, $5,000.  

2014  Ohio Environmental Protection Agency. Wetland Rehabilitation at The Rieck Center for Habitat Studies. Co-PI with Benjamin Dolan and Bethany Henderson-Dean, $93,500.

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