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Curvularia inaequalis
Curvularia inaequalis is a plant saprobe[1] that resides in temperate and subtropical environments.[2] It is commonly found in the soils of forage grasses and grains.[3] The species has been observed in a broad distribution of countries including Turkey, France, Canada, The United States, Japan and India.[4] This species is dematiaceous and a hyphomycete.[5] History and taxonomyThe Curvularia genus can be identified by its spiral borne phaeophragmospores, which contain both hyaline end cells and disproportionately large cells.[6] They possess conidia with differing curvature and number of septa.[6] C. inaequalis was first described in 1907 by ecologist Cornelius Lott Shear.[7] The fungus was isolated from diseased New Jersey cranberry pulp[7] and termed Helminthosporium inaequale.[6] Later, during Karl Boedijin's taxonomic organization and grouping of this genus, he recognized a similarity between them and H. inaequale.[6] He recognized a morphological similarity between its conidia and those of the lunata group within Curvularia, and so renamed it C. inaequalis.[6] Recognition of the three-septate curved conidia motivated the introduction of the now popularized name.[6] Growth and morphologyThe species' spore producing cells take on a model of sympodial growth.[6] Conidia grow through successive apices which end in a terminal prospore.[6] Growth can be affected by static magnetic fields with field flux densities.[8] Under these conditions, the number of conidia are able to increase by a minimum of 68 percent.[8] Curvularia inaequalis is a filamentous fungus, with 3 to 12 densely packed filaments.[7] The species is mostly brown in appearance, with pale brown end cells.[2][7] Conidia themselves, consist of 3-5 cells with thick cell walls and a larger central cell.[7][2] The diameter of the conidia ranges from 10 to 30 micrometers and have a slight leading curvature.[9][10] Overall the appearance of the species is described as looking "cottony" with clear branching cells.[2][7] The species can be difficult to identify due to its similar appearance to both C. and geniculate.[2] Instead, sequencing of nuclear rRNA internal transcribed spacer regions (ITS) can be done to achieve accurate identification.[2] PhysiologyThe optimal growth temperature for the species is 30°C.[7] It is able to produce a multitude of chemical products with enzymatic properties. One enzyme produced is chloroperoxidase, which can catalyze halogenation reactions.[11] Chloroperoxidase secreted from C. inaequalis contains vanadium active site.[5] The presence of the vanadium substrate vanadate is essential for the function of chloroperoxidase.[12] The compound glucose however, acts as an inhibitor for both enzyme function and production.[13] In its active form, the enzyme is able to then produce hypochlorous acid, a strong oxidizing agent.[5] It has been theorized that C. inaequalis utilizes chloroperoxidase and hypochlorous acid in combination to penetrate the host's cell wall.[5] Other significant compounds produced include of B-galactosidase, 4-hydroxyradianthin and Curvularone A. The species is able to produce large amounts of β-galactosidase, which can hydrolyze lactose in acid whey.[9] C. inaequalis also contains 4-hydroxyradianthin and Curvularone A compounds which have been identified as potential anti-tumor agents.[14] Pathology and toxicologyPlant pathology and toxicologyCurvularia inaequalis is known to cause leaf spot, also known as Leaf Blight.[10][15] Symptoms of infection by C. inaequalis include the combination of oval shaped dark brown patches and leaf tip dieback.[10] The infection slowly spreads causes necrosis until it has covered the entirety of the leaf.[10] It results in the thinning of grass vegetation such as Zoysia-, Bent-, Bermuda- and Buffalo- grasses.[10][15] Blighting is believed to be caused by two C. inaequalis mycotoxins, Pyrenocines A and B.[15] Pyrenocines A is the more potent of the two, stunting growth and causing necrosis in vegetation.[15] Both cause leaf tip die back in turf grass and leaf leakage of electrolytes in Bermuda grass.[15] Human pathologyCurvularia inaequalis is typically a rare human pathogen.[2] There are however, recorded medical cases that mention infection by the species. One such case is of an Eosinophilic fungal rhinosinusitis in an immunocompromised male.[16] Endoscopic sinus surgery was required to remove a large polyposis.[16] C. inaequalis was found to have grown favorably in the eosinophilic mucus.[16] Oral itraconazole and other corticosteroids successfully were administered to prevent reinfection.[16] Another case of C. inaequalis causing disease includes peritonitis in an elderly patient.[2] It is suggested that contraction of the fungus occurs due to contact with soils.[2] Furthermore, a case of recorded aerosolized C. inaequalis in one Canadian home supports airborne movement of spores as an important mode of transfer.[2] While many cases of infection due to soil contact with the genus Curvularia, connection with the specific species has not yet been confirmed.[2] Further studies are required to determine its human pathogen potential. References
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