Curvularia inaequalis

Curvularia inaequalis
Scientific classification
Domain:	Eukaryota
Kingdom:	Fungi
Division:	Ascomycota
Class:	Dothideomycetes
Order:	Pleosporales
Family:	Pleosporaceae
Genus:	Curvularia
Species:	C. inaequalis
Binomial name
Curvularia inaequalis (Shear) Boedijn (1907)
Synonyms
Helminthosporium inaequale Shear (1907) Acrothecium arenarium Moreau & V. Moreau (1941)

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]

The 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]

The 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]

The 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]

Curvularia 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]

Curvularia 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.