title: Acid protease production in fungal root endophytes.
abstract: Fungal endophytes are ubiquitous in healthy root tissue, but little is known about their ecosystem functions, including their ability to utilize organic nutrient sources such as proteins. Root-associated fungi may secrete proteases to access the carbon and mineral nutrients within proteins in the soil or in the cells of their plant host. We compared the protein utilization patterns of multiple isolates of the root endophytes Phialocephala fortinii s.l., Meliniomyces variabilis and Umbelopsis isabellina with those of two ectomycorrhizal (ECM) fungi, Hebeloma incarnatulum and Laccaria bicolor, and the wood-decay fungus Irpex lacteus at pH values of 2-9 on liquid BSA media. We also assessed protease activity using a fluorescently labeled casein assay and gelatin zymography and characterized proteases using specific protease inhibitors. I. lacteus and U. isabellina utilized protein efficiently, while the ECM fungi exhibited poor protein utilization. ECM fungi secreted metallo-proteases and had pH optima above 4, while other fungi produced aspartic proteases with lower pH optima. The ascomycetous root endophytes M. variabilis and P. fortinii exhibited intermediate levels of protein utilization and M. variabilis exhibited a very low pH optimum. Comparing proteolytic profiles between fungal root endophytes and fungi with well defined ecological roles provides insight into the ecology of these cryptic root associates.
authors.affiliation: Department of Biology, Mount Saint Vincent University, 166 Bedford Highway, Halifax, Nova Scotia, Canada, B3M 2J6.
authors.forename: Michael S
authors.initials: MS
authors.lastname: Mayerhofer
authors.affiliation: Department of Biology, Mount Saint Vincent University, 166 Bedford Highway, Halifax, Nova Scotia, Canada, B3M 2J6.
authors.forename: Erica
authors.initials: E
authors.lastname: Fraser
authors.affiliation: Department of Biology, Mount Saint Vincent University, 166 Bedford Highway, Halifax, Nova Scotia, Canada, B3M 2J6 gavin.kernaghan@msvu.ca.
authors.forename: Gavin
authors.initials: G
authors.lastname: Kernaghan
mesh_terms: D000143:Acids / Q000378:metabolism; D060026:Endophytes / Q000145:classification / Q000201:enzymology* / Q000235:genetics / Q000302:isolation & purification; D004795:Enzyme Stability; D005656:Fungal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D005658:Fungi / Q000145:classification / Q000201:enzymology* / Q000235:genetics / Q000302:isolation & purification; D006863:Hydrogen-Ion Concentration; D008969:Molecular Sequence Data; D038821:Mycorrhizae / Q000145:classification / Q000201:enzymology / Q000235:genetics / Q000302:isolation & purification; D010447:Peptide Hydrolases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010802:Phylogeny; D018517:Plant Roots / Q000382:microbiology*; D010944:Plants / Q000382:microbiology
chemical_list: D000143:Acids; D005656:Fungal Proteins; D010447:Peptide Hydrolases
keywords: Helotiales; aspartic protease; dark septate endophytes; ectomycorrhizal fungi; protein utilization; wood decay fungi