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Microscopic and Macroscopic Morphology of Curvularia clavata

Fernando Perez,Daniela Garcia Gonzales ,Erick Carranza,Bryan Ortiz
10.17966/JMI.2024.29.4.205 Epub 2025 January 03

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Abstract



Keywords



Curvularia clavata Dematiaceous fungi Morph- ology



Curvularia clavata is a dematiaceous, saprophytic, hetero- trophic fungus that is widely distributed in tropical and subtropical environments. Taxonomically, it belongs to the phylum Ascomycota, class Dothideomycetes, order Pleosporales, family Pleosporaceae, and is grouped in the genus Curvularia along with >232 species1,2. In humans, C. clavata is primarily associated with skin infections, such as phaeo- hyphomycosis, and sinusitis. In exceptional cases, it has been reported as a causative agent of invasive cerebritis2,3. In addition, in agro-industrial fields, it is reported as a plant pathogen, causing leaf spots, seed discoloration, and wilting in seedlings of crops such as Curcuma longa, Jatropha spp., Ananas comosus, and Zea mays2.

Curvularia clavata colonies have rapid growth; during the first 3 days, they show white colonies that later turn gray. On the fifth day, the colonies started turning olive green, and over time, they became black with a velvet-like texture and a fluffy center (Fig. 1A). The reverse side colonies are dark brown, with visible grooves and a clear halo at the periphery, without pigment production (Fig. 1B). Their optimal growth temperature is 20~25℃3. The conidia are smooth, either straight or curved, and have a claviform shape. Some cells are bigger than others and are colored pale to dark brown; apical and basal cells are both generally lighter. Their size ranges from 3~27 × 7~13.5 μm (Fig. 1C). The macrosiphon- ated mycelium with pigmented and segmented thick-wall hyphae are branched, pale to dark brown, with a diameter of 1.5~3.5 μm. Conidiophores can appear as isolated or in groups; commonly macronematous, they can also be observed as semi/mononematous. These conidiophores can be straight or curved, with cell walls thicker than vegetative hyphae, generally lighter at the top, and 34~102.5 × 2.5~5.5 μm2. Conidiogenous cells have smooth walls and can be in terminal or intercalary positions, proliferating sympodially. Their shape is subcylindrical or slightly swollen, being 5.5~17 × 4~6 μm2 (Fig. 1D).

For a more accurate description, molecular identification was performed by amplifying and sequencing the ribosomal internal transcribed spacer region. A sequence was deposited in GenBank under accession number PP373713.1.

Figure 1. (A) Front colony morphology of Curvularia clavata after 10 days of incubation on Sabouraud agar at 25℃. (B) Reverse colony morphology of Curvularia clavata after 5 days of incubation on Sabouraud agar at 25℃. (C) Conidia are smooth; either straight or curved with a claviform shape (lactophenol cotton blue, × 40). (D) A macrosiphonated mycelium with pigmented and segmented hyphae with thick, branched walls and color varying from pale to dark brown (lactophenol cotton blue, × 40).


References


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