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Curvularia pallescens
Scientific classification
Domain:	Eukaryota
Kingdom:	Fungi
Division:	Ascomycota
Class:	Dothideomycetes
Order:	Pleosporales
Family:	Pleosporaceae
Genus:	Curvularia
Species:	C. pallescens
Binomial name
	Curvularia pallescens; Boedijn (1933)
Synonyms
	Cochliobolus pallescens (Tsuda & Ueyama) Sivan. (1987); Pseudocochliobolus pallescens Tsuda & Ueyama (1983);

Curvularia pallescens is a soil fungus,^[1] that commonly grows on crops found in tropical regions.^[2]^[3] The conidia of the fungus are distinguishable from those of related species due to their lack of curvature.^[4]^[5] C. pallescens has been reported to cause infection in plants,^[6] and in immunocompetent individuals.^[1]^[4]^[7] This species is the anamorph of Cochliobolus pallescens.^[8]

Morphology

The colonies of C. pallescens differ in morphology depending on the growth medium used. On Czapek Yeast Extract Agar (CYA), colonies of C. pallescens are 50-65mm in diameter.^[5] On Malt Extract Agar (MEA), the colonies are fuzzy in texture, and pale grey to grey in colour. On the reverse side, they appear brown to dark brown. The colonies rapidly cover the entire Petri dish.^[5] On G25N, the colonies of C. pallescens are 3–6 mm in diameter, and appear grey and brown in colour. On Dichloran Chloramphenicol Malt Agar (DCMA), the colonies are 50–65 mm in diameter, and pale brownish-grey in colour. Lastly, colonies of C. pallescens grown on Phenylethyl Alcohol Agar (PEA) appear woolly at the centre.^[9] The conidiophores of C. pallescens are rarely branched, and are brown in colour.^[9] They can appear slightly bent at the apices, but otherwise they are predominately straight. The dimensions of the conidiophore vary, especially concerning its length. They can be up to 6μm wide.^[9] The conidia of C. pallescens are rugby or gridiron football- to bean-shaped, and are less curved than those of related species.^[5] They appear smooth in texture, and pale-brown to brown in colour.^[10] The three septa within each conidium give rise to four cells. The third cell from the base appears swollen in comparison to the surrounding cells. The dimensions of the conidia are 18-25 x 9-12 μm.^[5]

Cochliobolus pallescens is the teleomorphic form of Curvularia pallescens.^[8] It produces spherical ascomata that are black in colour.^[11] On the surface of the ascomata, there are protruding colourless necks from which the ascospores emerge.^[11] Ascospores are produced within cylindrical asci.^[11] The ascospores are colourless, and are either straight or slightly curved. Each ascospore contains 6-13 septa.^[11]

Ecology and growth

Curvularia pallescens is commonly found in tropical regions,^[2]^[3] such as India.^[12]^[13]^[5] They usually grow on unharvested crops (i.e., crops that have not been dried or stored),^[13] such as grass, rice, wheat, maize,^[13] and sorghum.^[5] Optimal growth occurs at 25-30 °C,^[14] and at an a_w of 0.976.^[13] The minimum a_w for growth is 0.89. Germination occurs at 0.855 a_w but does not result in the establishment of colonies.^[13] Sulphur and phosphorus are macronutrients involved in the production of DNA, RNA and proteins in fungal species.^[15] It has been reported that C. pallescens is able to grow and sporulate in the absence of both.^[15] Magnesium sulphide and tripotassium phosphate support the growth and sporulation of C. pallescens whereas, ammonium sulphate and ammonium phosphate do not.^[15]

Physiology

Curvularia pallescens acts as a biological reducing agent of AgNO₃, resulting in the production of silver nanoparticles (Ag NPs).^[16] This is considered a green method of Ag NP synthesis, unlike other methods that use chemical agents.^[16] Silver nanoparticles have widespread applications in industries such as healthcare, environmental health and drug-gene delivery.^[17] Curvularia pallescens has been reported to produce several secondary metabolites—particularly, isolates from spirostaphylotrichines and curvupallides. These two groups of secondary metabolites are structurally similar.^[18] Isolates of spirostaphylotrichines (i.e., C and D) were found to be phytotoxins whereas, the curvupallide isolates showed no phytotoxic activity. Despite the limited genome sequencing of this fungus,^[12] C. pallescens has been found to produce several enzymes with differing immunological and physiological functions in humans. These enzymes include BRN-1, vacuolar protease, fructose-bisphosphate aldolase, mannitol-1-phosphate 5-dehydrogenase, formate dehydrogenase, pyruvate decarboxylase, transketolase, peroxidase, catalase, phosphogluconate dehydrogenase and 14-3-3 protein.^[12] These proteins give C. pallescens its allergenic potential in humans. They have also been reported as allergens of other fungal species, and of species outside the kingdom Fungi.^[12]

Infection and disease

Curvularia pallescens has been reported to cause subcutaneous,^[4]^[7] pulmonary, and cerebral lesions,^[19]^[1] in immunocompetent individuals. It is thought that lesions arise as the result of inhalation of soils containing C. pallescens.^[1] The human pathogenic potential of C. pallescens stems from its viability and functionality at the normal human body temperature (37 °C),^[4] and its ability to disseminate.^[9] In addition to human infection, there have been multiple reported cases of leaf spots caused by C. pallescens, in crops. In particular, infections have occurred in bamboos (such as Bambusa vulgaris, Dendrocalamus longispathus and Thyrsostachys oliveri),^[20] sugarcanes, and grasses (such as Imperata arundinacea and Eleusine coracana).^[21] The severity of disease and the appearance of the spots differ between species. In B. vulgaris, the leaf spots appear circular or irregular in shape with a greyish-black centre and yellow perimeter.^[20] In sugarcane, the leaf spots appear elliptical in shape and light brown in colour.^[21] In I. arundinacea and E. coracana, the leaf spots appear irregular in shape and brown to black in colour.^[21] Curvularia pallescens invades the host organism via the stomata or proceeding damage. Infection arises as the result of the propagation of hyphae within the host, causing the host cell to rupture. This results in the spotty appearance on the leaf. Over time, the spots combine to form necrotic zones at the leaf tips causing dehydration in those areas.^[20] The leaf spots can be controlled by fungicide sprays, such as Mancozeb (0.1%). In addition to leaf spots, infection can result in: the hindrance of germination, inhibited growth of seedlings and mature crops of lesser quality (e.g., fewer grains produced, and the grains that are produced are damaged).^[14]

References

^ ^a ^b ^c ^d Friedman, Allan D.; Campos, Joseph M.; Rorke, Lucy B.; Bruce, Derek A.; Arbeter, Allan M. (September 1981). "Fatal recurrent Curvularia brain abscess". The Journal of Pediatrics. 99 (3): 413–415. doi:10.1016/S0022-3476(81)80331-9. PMID 7264797.
^ ^a ^b Ellis, M.B. (1971). Dematiaceous Hyphomycetes (1st ed.). England: CABI Publishing. ISBN 978-0851980270.
^ ^a ^b Farr, David F.; Bills, Gerald F.; Chamuris, George P.; Rossman, Amy Y. (1989). Fungi on Plants and Plant Products in the United States (2nd ed.). St. Paul, Minn.: APS Press. p. 1252. ISBN 0890540993.
^ ^a ^b ^c ^d Agrawal, Abha; Singh, S. M. (July 1995). "Two cases of cutaneous phaeohyphomycosis caused by". Mycoses. 38 (7–8): 301–303. doi:10.1111/j.1439-0507.1995.tb00412.x. PMID 8559194.
^ ^a ^b ^c ^d ^e ^f ^g Pitt, J.I.; Hocking, A.D. (1999). Fungi and Food Spoilage (2nd ed.). Gaithersburg, Md.: Aspen Publications. ISBN 0834213060.
^ "UAMH Centre for Global Microfungal Biodiversity". www.uamh.ca.
^ ^a ^b Berg, Daniel; Garcia, Julian A; Schell, Wiley A; Perfect, John R; Murray, John C (February 1995). "Cutaneous infection caused by Curvularia pallescens: A case report and review of the spectrum of disease". Journal of the American Academy of Dermatology. 32 (2): 375–378. doi:10.1016/0190-9622(95)90408-5. PMID 7829744.
^ ^a ^b "Curvularia pallescens". www.westerdijkinstitute.nl.
^ ^a ^b ^c ^d De Hoog, G. S.; Guarro, J.; Gene, J.; Figueras, M. J. (2001). Atlas of Clinical Fungi (2nd ed.). Netherlands: Amer Society for Microbiology. ISBN 9070351439.
^ Rippon, John Willard (1988). Medical mycology: the pathogenic fungi and the pathogenic actinomycetes (3rd ed.). Philadelphia, PA: Saunders. ISBN 978-0721624440.
^ ^a ^b ^c ^d Navi, S. S.; Bandyopadhyay, R; Hall, A. J.; Bramel-cox, Paula (1999). A pictorial guide for the identification of mold fungi on sorghum grain. International Crops Research Institute for the Semi-arid Tropics. p. 68. ISBN 978-92-9066-416-1.
^ ^a ^b ^c ^d Dey, Debarati; Saha, Bodhisattwa; Sircar, Gaurab; Ghosal, Kavita; Bhattacharya, Swati Gupta (July 2016). "Mass spectrometry-based identification of allergens from Curvularia pallescens, a prevalent aerospore in India". Biochimica et Biophysica Acta (BBA) - Proteins and Proteomics. 1864 (7): 869–879. doi:10.1016/j.bbapap.2016.03.012. PMID 27003473.
^ ^a ^b ^c ^d ^e Hocking, Ailsa D.; Miscamble, Beverly F.; Pitt, J.I. (January 1994). "Water relations of Alternaria alternata, Cladosporium cladosporioides, Cladosporium sphaerospermum, Curvularia lunata and Curvularia pallescens". Mycological Research. 98 (1): 91–94. doi:10.1016/S0953-7562(09)80344-4.
^ ^a ^b Almaguer, Michel; Rojas, Teresa Irene; Dobal, Vladimir; Batista, Amado; Aira, María Jesús (5 April 2012). "Effect of temperature on growth and germination of conidia in Curvularia and Bipolaris species isolated from the air". Aerobiologia. 29 (1): 13–20. doi:10.1007/s10453-012-9257-z.
^ ^a ^b ^c Bais, B. S.; Singh, S. B.; Singh, D. R.; Singh, D. V. (September 1972). "Sulphur and phosphorus requirements of Curvularia pallescens Boed". Mycopathologia et Mycologia Applicata. 47 (4): 363–368. doi:10.1007/BF02052347. PMID 4672786.
^ ^a ^b Elgorban, Abdallah M.; El-Samawaty, Abd El-Rahim M.; Abd-Elkader, Omar H.; Yassin, Mohamed A.; Sayed, Shaban R.M.; Khan, Mujeeb; Farooq Adil, Syed (November 2017). "Bioengineered silver nanoparticles using Curvularia pallescens and its fungicidal activity against Cladosporium fulvum". Saudi Journal of Biological Sciences. 24 (7): 1522–1528. doi:10.1016/j.sjbs.2016.09.019. PMC 6169509. PMID 30294221.
^ Siddiqi, Khwaja Salahuddin; Husen, Azamal; Rao, Rifaqat A. K. (16 February 2018). "A review on biosynthesis of silver nanoparticles and their biocidal properties". Journal of Nanobiotechnology. 16 (1): 14. doi:10.1186/s12951-018-0334-5. PMC 5815253. PMID 29452593.
^ Abraham, Wolf-Rainer; Meyer, Holger; Abate, Dawit (April 1995). "Curvupallides, a new class of alkaloids from the fungus Curvularia pallescens". Tetrahedron. 51 (17): 4947–4952. doi:10.1016/0040-4020(95)98692-B.
^ Lampert, Richard P.; Hutto, Jack H.; Donnelly, William H.; Shulman, Stanford T. (October 1977). "Pulmonary and cerebral mycetoma caused by Curvularia pallescens". The Journal of Pediatrics. 91 (4): 603–605. doi:10.1016/S0022-3476(77)80511-8. PMID 561837.
^ ^a ^b ^c Mohanan, C. (1997). Diseases of bamboos in Asia : an illustrated manual. International Network for Bamboo and Rattan, International Development Research Centre. pp. 41–42. ISBN 978-81-86247-20-4.
^ ^a ^b ^c Rao, G. P.; Singh, S. P.; Singh, Mathuresh (January 1992). "Two new alternative hosts of the leaf spot causing fungus of sugarcane". Tropical Pest Management. 38 (2): 218. doi:10.1080/09670879209371688.