Alternaria tenuissima
Species of fungus
From Wikipedia, the free encyclopedia
Alternaria tenuissima is a saprophytic fungus and opportunistic plant pathogen. It is cosmopolitan in distribution, and can colonize a wide range of plant hosts.[1] Colonies of A. tenuissima produce chains on agar growth media.[1] The fungus often forms concentric ring patterns on infected plant leaves.[2] This species produces the allergen Alt a 1, one of the most important outdoor seasonal fungal allergens associated with allergy and asthma provocation.[3] In rare circumstances, this species is also known to infect immunosuppressed humans and animals.[4]
| Alternaria tenuissima | |
|---|---|
Scientific classification  | |
| Kingdom: | Fungi |
| Division: | Ascomycota |
| Class: | Dothideomycetes |
| Order: | Pleosporales |
| Family: | Pleosporaceae |
| Genus: | Alternaria |
| Species: | A. tenuissima |
| Binomial name | |
| Alternaria tenuissima Samuel Paul Wiltshire (1933) | |
| Synonyms | |
| |
Growth and morphology
Unlike many other species of Alternaria, the conidiophores of A. tenuissima can develop in darkness after the colony has been exposed to light even very briefly; however its growth is more robust with longer periods of light exposure.[5] After 5–7 days in culture, colonies of A. tenuissima reach a diameter of 5 cm on PCA or V-8 agar (vegetable juice agar).[1] Colonies grown on PCA are brown in colour with a loose, cottony texture and bearing golden-brown conidia in chains.[1] Conidia are on the areas of the colony that receive the most light exposure, forming concentric sporulating rings of uncrowded conidial chains growing from branching hyphae on PCA.[1] Sporulation tends to be much more crowded in colonies grown on V-8 agar.[1] Simple unbranched and branched conidial chains of moderate length as well as solitary conidia are interspersed across the colony especially areas that receive little light.[1]
The light, golden-brown colour of the conidia, and their tendency to taper into long beaks, distinguish A. tenuissima from similar species notably A. alternata which produces dark brown conidia with short beaks.[4] Conidia of A. tenuissima also grow individually or in short chains[6] of 2-5 units,[1] while A. alternata tends to grow in longer chains.[7] Alternaria tenuissima conidia are smooth-walled[6] and have a median and subconstricting transverse septum.[1] Colonies of A. tenuissima on natural substrates (e.g., plant leaves) often develop a concentric, ringed pattern.[2]
Physiology
Alternaria tenuissima is a saprophyte, living on dead matter.[8] It produces the mycotoxins alternariol (AOH), alternariol methyl ester (AME), altenuene (ALT), altertoxin (ATX), and tenuazonic acid (TA), that are variously involved pathogenicity and interference competition.[8] Mycotoxins of this species are optimally produced at 25 °C.[9]
Habitat and ecology
Alternaria tenuissima is a cosmopolitan species, common on an array of various plant hosts in many countries spanning a range of environmental conditions.[10] It often colonizes blueberries,[11] tomatoes, grapevine, and strawberries.[7] It has also been found on several cereal grain species.[8] Optimal growth occurs between 25–30 °C (77–86 °F).[12] Although A. tenuissima is normally an opportunistic pathogen of plants, rare cases of skin infections in immunocompromised people have been reported.[13][14]
Medical significance
Cutaneous and subcutaneous alternariosis is a skin or tissue infection caused by members of the genus Alternaria, most commonly A. alternata and A. tenuissima.[4] Because of the inability of A. tenuissima to invade healthy host tissue, alternariosis tends to be restricted to people with abrogated cellular immunity and occasionally the elderly.[4] Complication following organ transplantion, Cushing's syndrome and immunosuppressive therapies are some of the typical settings in which alternariosis has been reported.[4] Alternariosis appears on the skin as red pustules that may produce ulcers over time.[4] Alternaria tenuissima is a prolific producer of the allergen Alt a 1.[15] Exposure to this protein can induce an allergic reaction in sensitized individuals by reacting with circulating IgE antibody.[3] Exposure to Alt a 1 has been associated with asthmatic exacerbation.[16] Alternaria tenuissima also produces the mycotoxin tenuazonic acid[17] which has received attention as a candidate antitumor medication.[18]