Fungalpedia – Note 3254, Aphelidiomycota

 

Aphelidiomycota Tedersoo, Sanchez-Ramirez, Kõljalg, Bahram, M. Döring, Schigel, T.W. May, M. Ryberg & Abarenkov, Fungal Diversity 90: 147 (2018).

Citation when using this data: Wijayawardene NN et al. 2024 – Fungalpedia.

Index Fungorum, Faceoffungi, MycoBank, GenBank, Fig 1.

Classification: Aphelidiomyceta, Fungi.

Amoeboid endobiotic parasites of algae. Dispersal amoeboid zoospores attach to a new host cell and encyst (either sessile on the substrate or producing a stalk; “apophyse”; Gromov 2000). Amoeboid body penetrates the host’s cell through a cyst stalk. The intracellular amoeba engulfs the contents of the host’s cell, forming food vacuoles that transport food into the central digestive vacuole. An excretory body is formed in the digestive vacuole. The amoeboid trophont grows into a plasmodium, which totally replaces the cytoplasm of a host cell; the multinuclear plasmodium develops into an unwalled sporangium and divides into uninucleate amoeboid zoospores. Intracellular resting spores are present (Karpov et al. 2014a).

Life modes and distribution: parasites of algae

Notes: The aphelids are a small group of intracellular parasites of algae, including three freshwater genera, Aphelidium (Zopf) Gromov (Fig. 1), Amoeboaphelidium Scherff., Paraphelidium Karpov et al. and a marine genus, Pseudaphelidium Schweikert & Schnepf (Schweikert and Schnepf 1996, 1997; Gromov 2000; Karpov et al. 2017a). 

Only the asexual part of the life cycle is known for aphelids: amoeboid zoospore attaches to the host algae, and involves a flagellum and encysts. A cyst germinates and penetrates the host cell wall with an infection tube and injects the cyst contents into the host. The parasite becomes the intracellular phagotrophic amoeba which engulfs the host cytoplasm with pseudopodia and forms a central digestive vacuole containing a red residual body. The parasite grows forming an endobiotic multinucleate plasmodium with the residual body in a large central vacuole while it consumes the whole cytoplasm of the host cell. The mature plasmodium then divides into a number of uninucleated cells. After maturation, the amoeboid zoospores are released from the empty host cell through the hole made earlier by the infection tube and infect other algae. 

All known aphelids can produce multiple infections, thus, the trophonts from different strains/populations may fuse to each other during the development of plasmodium which can possess more than one sort of nuclei (Tcvetkova et al. 2023). 

The phylogenetic position of the aphelids became clear after five genes sequencing of Amoeboaphelidium protococcorum (Karpov et al. 2013). Subsequently, Letcher et al. (2013) confirmed this result on the base of SSU gene sequence of Am. occidentale. The aphelids grouped with Rozella and microsporidia forming a cluster sister to Fungi, which was called the super phylum Opisthosporidia a year later (Karpov et al. 2014a). The rank of the aphelids has been raised from the class Aphelidae (Gromov 2000) to the phylum Aphelida (Karpov et al. 2014a). The position of the aphelids on ribosomal trees was not stable. It varied from sister group to Fungi+(Rozella+Microsporidia) (Corsaro et al. 2014, 2019), to Rozella+Microsporidia (in most published trees), and to the Fungi (Tedersoo et al. 2018). Many mycologists included aphelids in the Fungi based predominantly on their life cycle, which superficially resembles those of zoosporic fungi, and on the monophyly of the cluster including Fungi and Opisthosporidia (James et al. 2013). The subsequent outline by Wijayawardene et al. (2020a) followed Tedersoo et al. (2018) and listed Aphelidiomycota as a distinct phylum in the fungal clade.

Intensive study of the aphelids during last decade gave more knowledge based on the light microscopic and ultrastructural observations, and molecular phylogeny including genomics. A new genus Paraphelidium with two species was described (Karpov et al. 2017a, b), several new species in Aphelidium (Letcher et al. 2017; Tcvetkova et al. 2019; Seto et al. 2020, 2022) and Amoeboaphelidium (Letcher et al. 2015) were added based on morphological and molecular data. Genomes of two (Mikhailov et al. 2022) and transcriptomes of four aphelid species (Torruella et al. 2018; Galindo et al. 2022) were assembled, and a multigene phylogeny unambiguously showed a sister position of the Aphelida and fungi.

Karpov et al. (2014a, b) believe that phylum Aphelidiomycota (=Aphelida) having a phagotrophic cellular mode of nutrition does not belong to the kingdom Fungi with the totally saprotrophic cellular mode of nutrition. From this view, the original phylum name Aphelida (Karpov et al. 2014a) has to be retained. We temporarily accept the layout of the present paper dealing with Fungi sensu lato, which also includes here the phagotrophic rozellids and follows the taxonomy by Tedersoo et al. (2018). 

Currently, the phylum consists of one subphylum (Aphelidiomycotina) and one class (Aphelidiomycetes).

Type genus: Aphelidium Zopf 1885.

Other accepted species: Species Fungorum – search Aphelidiomycota.

 

 

Figure 1 – Light microscopic images of three stages of life cycle of Aphelidium spp. life cycle. Modified after: Karpov et al. (2014b) (e,f,g), 2020 (a,b,h), Tcvetkova et al. (2019) (c,d). a-e – zoospores of Aph. insulamus (a,b), Aph. arduennense (c,d) and Aph. melosirae (e); a,c,e Swimming zoospores. b,d Crawling zoospores with simple filopodia (f) and branching filopodia (bf). f Plasmodium of Aph. melosirae in the host cell with central digestive vacuole (cv) containing residual body (rb). g Rounded resting spore (rs) of Aph. melosirae. h elongated resting spore (rs) of Aph. insulamus. Scale bars: a-e = 3 µm, f-h = 10 µm. 

 

References

Corsaro D, Walochnik J, Venditti D, Steinmann J et al. 2014 – Microsporidia-like parasites of amoebae belong to the early fungal lineage Rozellomycota. Parasitol Res 113:1909–1918.

Corsaro D, Wylezich C, Venditti D, Michel R et al. 2019 – Filling gaps in the microsporidian tree: rDNA phylogeny of Chytridiopsis typographi (Microsporidia: Chytridiopsida). Parasitol Research 118:169–180.

Gromov BV. 2000 – Algal parasites of the genera Aphelidium, Amoeboaphelidium and Pseudoaphelidium from the Cienkovski’s ‘‘Monadea’’ group as representatives of a new class. Zool Zh 79:517–525 (in Russian)

Karpov SA, Mamkaeva MA, Aleoshin VV, Nassonova E et al. 2014a – Morphology, phylogeny, and ecology of the aphelids (Aphelidea, Opisthokonta) and proposal for the new superphylum Opisthosporidia. Front. Microbiol. 5:112.

Karpov SA, Mikhailov KV, Mirzaeva GS, Mirabdullaev IM et al. 2013 – Obligately phagotrophic aphelids turned out to branch with the earliest diverging fungi. Protist 164:195–205.

Karpov SA, Torruella G, Moreira D, Mamkaeva MA et al. 2017b – Molecular phylogeny of Paraphelidium letcheri sp. nov. (Aphelida, Opisthosporidia). J Eukaryot Microbiol 5:573–578. 

Letcher PM, Longcore JE, Quandt CA, da Silva Leite D et al. 2017 – Morphological, molecular, and ultrastructural characterization of Rozella rhizoclosmatii, a new species in Cryptomycota. Fungal Biol 121:1–10.

Letcher PM, Lopez S, Schmieder R, Lee PA et al. 2013 – Characterization of Amoeboaphelidium protococcarum, an algal parasite new to the Cryptomycota isolated from an outdoor algal pond used for the production of biofuel. PLoS ONE 8(2):e56232.

Letcher PM, Powell MJ, Lopez S, Lee PA, McBride RC. 2015 – A new isolate of Amoeboaphelidium protococcarum, and Amoeboaphelidium occidentale, a new species in phylum Aphelida (Opisthosporidia). Mycologia 107(3):522–531.

Mikhailov KV, Karpov SA, Letcher PM, Lee PA et al. 2022 – Genomic analysis reveals cryptic diversity in aphelids and sheds light on the emergence of Fungi. Curr Biol 32 (21):4607–4619.

Schweikert M, Schnepf E. 1996 – Pseudaphelidium drebesii, genet specnov (incerta sedis), a Parasite of the Marine Centric Diatom Thalassiosira punctigera. Archiv für Protistenkunde. 147(1):11–17.

Schweikert M, Schnepf E. 1997 – Electron microscopical observations on Pseudaphelidium drebesii Schweikert and Schnepf, a parasite of the centric diatom Thalassiosira punctigera. Protoplasma 199:113–123.

Seto K, Matsuzawa T, Kuno H, Kagami M. 2020 –Morphology, ultrastructure, and molecular phylogeny of Aphelidium collabens sp. nov. (Aphelida), a parasitoid of a green alga Coccomyxa sp. Protist 171(3):125728. 

Seto K, Nakada T, Tanabe Y, Yoshida M et al. 2022 – Aphelidium parallelum sp. nov., a new aphelid parasitic on selenastracean green algae. Mycologia 114(3):544–555.

Tcvetkova VS, Pozdnyakov IR, Seliuk AO, Zorina NA et al. 2023 – Vegetative cell fusion and a new stage in the life cycle of the Aphelida (Opisthosporidia). Journal of Eukaryot Microbiol 70: e012977.

Tcvetkova VS, Zorina NA, Mamkaeva MA, Karpov SA. 2019 – Molecular phylogeny of Aphelidium arduennense sp. nov.-new representative of Aphelida (Opisthosporidia). Protistol 13(4):192–198.

Tedersoo L, Sánchez-Ramírez S, Kõljalg U, Bahram M et al. 2018 – High-level classification of the Fungi and a tool for evolutionary ecological analyses. Fungal Divers 90:135–159.

Torruella G, Grau-Bove X, Moreira D, Karpov SA et al. 2018 – Global transcriptome analysis of the aphelid Paraphelidium tribonemae supports the phagotrophic origin of fungi. Communications biology 1:231.

Wijayawardene NN, Hyde KD, Al-Ani LKT, Tedersoo L et al. 2020a – Outline of Fungi and fungus-like taxa. Mycosphere 11:1060–1456.

 

Entry by

Nalin N. Wijayawardene, Center for Yunnan Plateau Biological Resources Protection and Utilization, College of Biological Resource and Food Engineering, Qujing Normal University, Qujing, Yunnan 655011, P.R. China, Tropical Microbiology Research Foundation, 96/N/10, Meemanagoda Road, 10230 Pannipitiya, Sri Lanka, Department of Bioprocess Technology, Faculty of Technology, Rajarata University, Sri Lanka

 

Published online 25 September 2026

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