Celebrating INVAM: 35 years of the largest living culture collection of arbuscular mycorrhizal fungi.

The International Culture Collection of (Vesicular-) Arbuscular Mycorrhizal Fungi-INVAM-the largest living culture collection of arbuscular mycorrhizal fungi (AMF) celebrated its 35th year in 2020. The authors record here the mission and goals of INVAM, its contribution as a living culture collection, some historical aspects of INVAM, and describe the advances in mycorrhizology and AMF systematics after INVAM moved to West Virginia University. This commentary emphasizes the importance of a living culture collection to preserve germplasm and to educate and assist researchers in mycorrhizal science.

Urine Antigen Testing is Equally Sensitive to B. dermatitidis and B. gilchristii Infections.

INTRODUCTION: Blastomycosis is endemic in Wisconsin with Blastomyces dermatitidis and B. gilchristii responsible for infections. Urine antigen testing is a non-invasive diagnostic method for blastomycosis with up to 93% test sensitivity. However, the test's sensitivity has not been evaluated with relationship to B. gilchristii infections. METHODS: We aimed to assess physician use of the urine antigen assay and its sensitivity to B. gilchristii and B. dermatitidis infections in a retrospective study. Culture confirmed clinical cases of blastomycosis from 2008-2016 were identified within Marshfield Clinic Health System (MCHS) and UW Hospital and Clinics (UWHC) medical records. Clinical data were abstracted from each medical record and included the following: patient demographics, presence of immune compromising and underlying medical conditions, treatment drugs, presence of isolated pulmonary or disseminated disease, death, urine antigen testing, timeframe of testing, and quantitative test values (EIA units or ng/mL). RESULTS: A total of 140 blastomycosis cases were included in this study, with MCHS contributing 114 cases to the study and UWHC contributing 26 cases. The majority of UWHC cases (n=22; 85%) were caused by B. dermatitidis and the majority of MCHS cases (n=73; 64%) were caused by B. gilchristii. UWHC physicians were significantly more likely to treat with multiple drugs during the course of infection and were more likely to prescribe amphotericin B and voriconazole. Urine antigen testing was more frequently used at UWHC (n=24; 92%) than MCHS (n=51; 45%; P < 0.00001). In this study, the urine antigen assay demonstrated 79% sensitivity. Sensitivity was significantly associated with the timeframe of testing (P < 0.05), with most true positive urine antigen tests (83%) being performed ≤ 7 days from diagnosis. In this study, the urine antigen assay was capable of detecting both B. dermatitidis and B. gilchristii at about equal sensitivity. Urine antigen concentration (ng/mL) trended higher in B. dermatitidis infections. CONCLUSION: This study found that the urine antigen assay is capable of detecting both species of Blastomyces at about the same sensitivity. We recommend continued use of the urine antigen assay for diagnosis of blastomycosis and recommend that the assay be used early in the diagnostic process to minimize the chance of false negative results.

Cellular organization in germ tube tips of Gigaspora and its phylogenetic implications.

Comparative morphology of the fine structure of fungal hyphal tips often is phylogenetically informative. In particular, morphology of the Spitzenkörper varies among higher taxa. To date no one has thoroughly characterized the hyphal tips of members of the phylum Glomeromycota to compare them with other fungi. This is partly due to difficulty growing and manipulating living hyphae of these obligate symbionts. We observed growing germ tubes of Gigaspora gigantea, G. margarita and G. rosea with a combination of light microscopy (LM) and transmission electron microscopy (TEM). For TEM, we used both traditional chemical fixation and cryo-fixation methods. Germ tubes of all species were extremely sensitive to manipulation. Healthy germ tubes often showed rapid bidirectional cytoplasmic streaming, whereas germ tubes that had been disturbed showed reduced or no cytoplasmic movement. Actively growing germ tubes contain a cluster of 10-20 spherical bodies approximately 3-8 µm behind the apex. The bodies, which we hypothesize are lipid bodies, move rapidly in healthy germ tubes. These bodies disappear immediately after any cellular perturbation. Cells prepared with cryo-techniques had superior preservation compared to those that had been processed with traditional chemical protocols. For example, cryo-prepared samples displayed two cell-wall layers, at least three vesicle types near the tip and three distinct cytoplasmic zones were noted. We did not detect a Spitzenkörper with either LM or TEM techniques and the tip organization of Gigaspora germ tubes appeared to be similar to hyphae in zygomycetous fungi. This observation was supported by a phylogenetic analysis of microscopic characters of hyphal tips from members of five fungal phyla. Our work emphasizes the sensitive nature of cellular organization, and the need for as little manipulation as possible to observe germ tube structure accurately.

Comparisons of AM fungal spore communities with the same hosts but different soil chemistries over local and geographic scales.

Arbuscular mycorrhizal (AM) fungi are ubiquitous and ecologically important microbes in grasslands. Both the host plant species and soil properties have been suggested as potentially important factors structuring AM fungal communities based on studies within local field sites. However, characterizations of the communities in relation to both host plant identity and soil properties in natural plant communities across both local and broader geographic scales are rare. We examined the AM fungal spore communities associated with the same C(4) grasses in two Eastern serpentine grasslands, where soils have elevated heavy metals, and two Iowa tallgrass prairie sites. We compared AM fungal spore communities among host plants within each site, looked for correlations between fungal communities and local soil properties, and then compared communities among sites. Spore communities did not vary with host plant species or correlate with local soil chemical properties at any site. They did not differ between the two serpentine sites or between the two prairie sites, despite geographic separation, but they did differ between serpentine and prairie. Soil characteristics are suggested as a driving force because spore communities were strongly correlated with soil properties when data from all four sites are considered, but climatic differences might also play a role.

Evidence for ecological matching of whole AM fungal communities to the local plant-soil environment.

The range of ecological roles exhibited by arbuscular mycorrhizal (AM) fungi depends on functional differences among naturally occurring local assemblages of AM species. While functional differences have been demonstrated among AM fungal species and among geographic isolates of the same species, almost nothing is known about functional differences among whole communities of naturally occurring AM fungi. In the greenhouse, we reciprocally transplanted whole AM fungal communities between plant-soil systems representing a serpentine grassland and a tallgrass prairie, using as hosts two grasses common to both systems. For Sorghastrum nutans, native fungi consistently enhanced plant growth more than fungi switched from the alternate system. For Schizachyrium scoparium, foreign and native fungi promoted plant growth similarly in both the serpentine and prairie systems. Thus, the use of foreign inoculum in restoration could change the relative performance, and potentially the competitive abilities, of co-occurring plant species. Moving AM fungal inocula into foreign environments also caused changes in the taxonomic composition of the resultant spore communities, demonstrating their response to environmental influences. These results provide strong evidence for functional differences among naturally occurring AM communities and suggest that a particular AM fungal community may be better matched ecologically to its local habitat than communities taken from other locations.

Plant-soil feedback: testing the generality with the same grasses in serpentine and prairie soils.

Plants can alter soil properties in ways that feed back to affect plant performance. The extent that plant-soil feedback affects co-occurring plant species differentially will determine its impact on plant community structure. Whether feedback operates consistently across similar plant communities is little studied. Here, the same grasses from two eastern U.S. serpentine grasslands and two midwestern tallgrass prairie remnants were examined for plant-soil feedback in parallel greenhouse experiments. Native soils were homogenized and cultured (trained) for a year with each of the four grasses. Feedback was evaluated by examining biomass variation in a second generation of (tester) plants grown in the trained soils. Biomass was lower in soils trained by conspecifics compared to soils trained by heterospecifics in seven of 15 possible cases; biomass was greater in conspecific soils in one other. Sorghastrum nutans exhibited lower biomass in conspecific soils for all four grasslands, so feedback may be characteristic of this species. Three cases from the Hayden prairie site were explained by trainer species having similar effects across all tester species so the relative performance of the different species was little affected; plants were generally larger in soils trained by Andropogon gerardii and smaller in soils trained by S. nutans. Differences among sites in the incidence of feedback were independent of serpentine or prairie soils. To explore the causes of the feedback, several soil factors were measured as a function of trainer species: nutrients and pH, arbuscular mycorrhizal (AM) spore communities, root colonization by AM fungi and putative pathogens, and functional diversity in bacterial communities as indicated by carbon substrate utilization. Only variation in nutrients was consistent with any patterns of feedback, and this could explain the greater biomass in soils trained by A. gerardii at Hayden. Feedback at Nottingham (one of the serpentine sites) differed, most notably for A. gerardii, from that of similar past studies that used different experimental protocols. To understand the consequences of feedback for plant community structure, it is important to consider how multiple species respond to the same plant-induced soil variation as well as differences in the feedback detected between greenhouse and field settings.