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Fungi are a diverse group of eukaryotic organismsrepresenting evolutionary lines that are distinct fromthose of plants or animals. More than 80,000 species offungi have been described; however, most mycologistsbelieve at least 1.5 million species of fungi exist. Themajority of fungi reproduce by means of spores thatare adapted for airborne dispersal. As a result, airbornefungal spores are an ever-present part of the environ-ment and can be found both outdoors and indoors. Thespores of many fungi are well-recognized allergens. Inaddition, some fungi are known to cause human infec-tions, and some produce mycotoxins.

February 2004 J ALLERGY CLIN IMMUNOL

Estelle Levetin, PhD, Guest Editor

An atlas of fungal spores

From the Faculty of Biological Science, The University of Tulsa, Tulsa,Okla.

Received for publication September 23, 2003; revised September 23,2003; accepted for publication September 25, 2003.

Reprint requests: Estelle Levetin, PhD, Department of BiologicalScience, The University of Tulsa, 600 S College, Tulsa, OK 74104.

J Allergy Clin Immunol 2004;113:366-8.0091-6749/$30.00© 2004 American Association of Allergy, Asthma and Immunologydoi:10.1016/j.jaci.2003.09.049

FIG 1. Fall air sample from Tulsa, Oklahoma, showscomponents of the dry air spora that dominate theatmosphere during warm, dry, and windy weather.Spores of many fungi are included in this category;however, this image only shows conidia ofCladosporium, Alternaria, Pithomyces, andCurvularia species and smut teliospores. A ragweedpollen grain is also visible in the lower portion of thephoto. All of the spores visible in this image areknown allergens.

FIG 2. Conidia from Cladosporium species are themost abundant airborne spores in many parts of theworld, occurring both indoors and outdoors. Hourlyatmospheric concentrations of these spores in excessof 200,000 spores/m3 have been registered duringhigh winds. Species of Cladosporium normally existas saprobes or weak plant pathogens and are readilyisolated from leaf surfaces. The spores are known tobe allergenic, and there have been some reports ofCladosporium species infections in immune-com-prised individuals. The lightly pigmented spores areproduced in branching chains and show refractiveattachment scars. The ornamented spores ofCladosporium herbarum in this air sample photo areall nonseptate (single celled); however, otherCladosporium spores can have 1 to 3 cells andsmooth walls. In the older allergy literature, somespecies of Cladosporium were called Hormodendrum.

FIG 3. Alternaria species are characterized by largemulticellular spores with both transverse and longitu-dinal septa (cross-walls) and a distinct beak. Thesedeeply pigmented conidia are produced in chains, andat the tip of the beak, there is usually a refractiveattachment scar. They are frequently the second mostabundant spore type in the dry air spora. Species ofAlternaria are pathogenic to a number of crop plantsbut also occur as saprobes on a variety of organic sub-strates, including indoor substrates. Alternaria conidiaare allergenic and have been associated with severeasthma. Infections in immune-compromised patientshave been reported.

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FIG 5. Aspergillus niger is one of the commonspecies of Aspergillus, a genus characterized by glo-bose heads of conidia. In nature this genus is wide-spread, typically occurring in the soil. VariousAspergillus species are a major cause of decay ofagricultural crops in the field and in storage, andmany species are also common in contaminatedindoor environments. Aspergillus conidia are aller-genic, and several species (especially Aspergillusfumigatus) cause aspergillosis in immune-compro-mised individuals. In addition, many species ofAspergillus are known to produce mycotoxins.

FIG 6. This scanning electron micrograph of a conidi-al head of Aspergillus niger shows developing coni-dia produced by phialides (visible beneath thespores). Individual conidia are approximately 3 to 4µm in diameter and ornamented with irregular wartsand ridges. Long chains of conidia are normally pro-duced, but only short chains are visible in this youngconidial head.

FIG 7. Ganoderma applanatum basidiocarps (fruitingbodies) growing from the base of a tree. Species ofGanoderma are wood-decay fungi attacking both liv-ing and dead hardwoods and conifers. This genus,which has a worldwide distribution, is easily distin-guished from other bracket fungi by the uniquespores (see Fig 8). A closely related species,Ganoderma lucidum, is widely used in Chineseherbal medicine to treat everything from cardiovas-cular disease to Alzheimer’s disease to asthma.

FIG 4. Conidia from Curvularia species are often pre-sent in the outdoor air. The distinctive thick-walledspores are pigmented and normally have 3 or 4transverse septa. The end cells are frequently lighterin color, and the spores are typically curved becauseof the asymmetric enlargement of the central cell. Aprotuberant basal attachment structure is visible onmost spores. Curvularia species occur as saprobesand plant pathogens causing leaf-spot disease onvarious crops. Spores are allergenic and have beenincreasingly implicated in allergic fungal sinusitis.

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FIG 8. Ganoderma spores are the most distinctivebasidiospores in the atmosphere, with a golden innerwall and a transparent, smooth outer wall. Interwallconnections and a prominent germ pore with a trun-cated apex are also characteristic features. In someparts of the world, these basidiospores are the domi-nant component of the air spora for several monthsof each year. Allergenicity of Ganoderma speciesbasidiospores along with basidiospores from otherfungi have been reported in numerous clinical stud-ies.

FIG 9. Fungal contamination on ceiling tiles in aschool bathroom resulted from a plumbing leak onthe floor above. Samples from the tiles showed thatthe contamination was entirely Stachybotrys char-tarum. This species is commonly found indoors onwet materials containing cellulose, such as wall-board, ceiling tiles, wicker, straw, cardboard, andpaper. It has been shown to be allergenic, althoughlittle research has been done on the allergens. Also,some strains of Stachybotrys are well known to pro-duce potent mycotoxins. There has been a great dealof recent controversy and concern about the possiblehealth effects caused by this fungus.

FIG 10. An air sample from a water-damaged homeshowed fungal spores at a concentration of morethan 1 million spores per cubic meter. Visible in thisfigure are Penicillium/Aspergillus-type conidia (small,colorless, ornamented, globose spores),Stachybotrys conidia (black cylindrical spores),Cladosporium sphaerospermum conidia (pigmentedsubglobose spores at upper left), and a singleChaetomium species ascospore (lemon-shapedspore at lower right).

The author wishes to thank Richard Portman for hisassistance with the scanning electron microscope.