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] The species belongs to the group of dematiaceous hyphomycetes.[5]

Curvularia inaequalis
Scientific classification
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)

History and taxonomy

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] Curvularia species 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] It was later renamed as Curvularia inaequalis, by Karl Boedijin.[6] During his taxonomic organization and grouping of the Curvularia species, Boedijin recognized a similarity between the conidia of C. inaequalis and of the ‘lunata’ Curvularia group.[6] Recognition of the three-septate curved conidia motivated the introduction of the now popularized name.[6]

Growth and morphology

The species’ spore producing cells take on a model of sympodial growth.[6] Conidia grow through successive apices which end in a terminal porospore.[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]

C. 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 Curvularia lunata and Curvularia geniculate.[2] Instead, sequencing of nuclear rRNA internal transcribed spacer regions (ITS) can be done to achieve accurate identification.[2]

Physiology

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 vandium 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 B-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 toxicology

Plant pathology and toxicology

C. inaequalis is known to cause leaf spot, also known as Leaf Bligh.[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 Buffalograss.[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 pathology

C. 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.

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References
  1. Ayoubi, Najmeh; Soleimani, Mohammad Javad; Zare, Rasoul; Zafari, Doustmorad (1 August 2017). "First report of Curvularia inaequalis and C. spicifera causing leaf blight and fruit rot of strawberry in Iran". Nova Hedwigia. 105 (1): 75–85. doi:10.1127/nova_hedwigia/2017/0402.
  2. Pimentel, J. D.; Mahadevan, K.; Woodgyer, A.; Sigler, L.; Gibas, C.; Harris, O. C.; Lupino, M.; Athan, E. (4 August 2005). "Peritonitis Due to Curvularia inaequalis in an Elderly Patient Undergoing Peritoneal Dialysis and a Review of Six Cases of Peritonitis Associated with Other Curvularia species". Journal of Clinical Microbiology. 43 (8): 4288–4292. doi:10.1128/JCM.43.8.4288-4292.2005. PMID 16082004.
  3. Sivanesan, A. (1987). Graminicolous species of bipolaris, curvularia, drechslera, exserohilum and their teleomorphs. England: C.A.B International. ISBN 0851985874.
  4. Moubasher, A.H.; Zeinab, Soliman; Abdel-Sater, M.A. (2018). "Contribution to the mycobiota of Egypt: 25 new records and interesting fungal taxa from citrus and grapevine plantations". Journal of Basic & Applied Mycology (Egypt). 9: 43.
  5. Messerschmidt, A.; Wever, R. (9 January 1996). "X-ray structure of a vanadium-containing enzyme: chloroperoxidase from the fungus Curvularia inaequalis". Proceedings of the National Academy of Sciences. 93 (1): 392–396. doi:10.1073/pnas.93.1.392. PMC 40244. PMID 8552646.
  6. Kendrick, W. B.; Cole, G. T. (October 1968). "Conidium ontogeny in hyphomycetes. The sympodulae of Beauveria and Curvularia". Canadian Journal of Botany. 46 (10): 1297–1301. doi:10.1139/b68-172.
  7. Shear, Cornelius Lott; Stevens, Neil Everett; Bain, Henry F. (1931). Fungous diseases of the cultivated cranberry. Champaign, Illinois: United States Department of Agriculture. pp. 1–58.
  8. Nagy, P.; Fischl, G. (May 2004). "Effect of static magnetic field on growth and sporulation of some plant pathogenic fungi". Bioelectromagnetics. 25 (4): 316–318. doi:10.1002/bem.20015. PMID 15114642.
  9. Laurila, Heikki O.; Nevalainen, Helena; Mikinen, Veijo (February 1985). "Production of protoplasts from the fungi Curvularia inaequalis and Trichoderma reesei". Applied Microbiology and Biotechnology. 21 (3–4): 210–212. doi:10.1007/BF00295124.
  10. Amaradasa, B. S.; Amundsen, K. (February 2014). "First Report of Curvularia inaequalis and Bipolaris spicifera Causing Leaf Blight of Buffalograss in Nebraska". Plant Disease. 98 (2): 279. doi:10.1094/PDIS-05-13-0487-PDN. PMID 30708754.
  11. Lesk, Arthur (2012). Introduction to genomics (2nd ed.). United Kingdom: Oxford University Press. p. 339. ISBN 978-0199564354.
  12. van Schijndel, Johannes W.P.M.; Vollenbroek, Esther G.M.; Wever, Ron (February 1993). "The chloroperoxidase from the fungus Curvularia inaequalis; a novel vanadium enzyme". Biochimica et Biophysica Acta (BBA) - Protein Structure and Molecular Enzymology. 1161 (2): 249–256. doi:10.1016/0167-4838(93)90221-C.
  13. Barnett, Philip; Kruitbosch, Danny L; Hemrika, Wieger; Dekker, Henk L; Wever, Ron (May 1997). "The regulation of the vanadium chloroperoxidase from Curvularia inaequalis". Biochimica et Biophysica Acta (BBA) - Gene Structure and Expression. 1352 (1): 73–84. doi:10.1016/S0167-4781(96)00238-2. PMID 9177485.
  14. Pang, Yan-Wei; Zhang, Ling-Jian; Fang, Jia-Shuang; Liu, Qian-Feng; Zhang, Hui; Xiang, Wen-Sheng; Wang, Ji-Dong; Wang, Xiang-Jing (23 January 2013). "Two new antitumor constituents from a soil fungus Curvularia inaequalis (strain HS-FG-257)". The Journal of Antibiotics. 66 (5): 287–289. doi:10.1038/ja.2012.128. PMID 23340662.
  15. Kim, Jin-Cheol; Choi, Gyung Ja; Kim, Heung Tae; Kim, Hyun-Ju; Cho, Kwang Yun (June 2000). "Pathogenicity and Pyrenocine Production of Curvularia inaequalis Isolated from Zoysia Grass". Plant Disease. 84 (6): 684–688. doi:10.1094/PDIS.2000.84.6.684. PMID 30841112.
  16. Posteraro, B.; Posteraro, E.; Sorda, M.; Torelli, R.; De Corso, E. (2010). "Eosinophilic fungal rhinosinusitis due to the unusual pathogen Curvularia inaequalis". Mycoses. 53 (1): 84–88. doi:10.1111/j.1439-0507.2008.01671.x. PMID 19207840.
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