The genus Wallemia is xerophilic. Three species of Wallemia have been identified. These are W. ichthyophaga, W. sebi, and W. muriae. Wallemia sebi is the most well known species. It has been isolated from air, soil, dried food (causing spoilage) and salt. Since the species within the genus Wallemia have been recognized only recently, little is known about their mechanisms of adaptation to low water activity substrates.
Wallemia sebi has a world-wide distribution. It is common in indoor environments and has been isolated from jams, dates, bread, cakes, salted beans and fish, bacon, fruits, soil, hay, and textiles. It is also common in agricultural environments where it is suspected to be one of the causes of farmer’s lung disease and other human allergies.
Wallemia sebi produces extremely tiny spores (even smaller than spores of some species of Penicillium or Aspergillus) that are reported to be highly allergenic. Their small size would certainly allow for efficient invasion of the respiratory system. Some strains of Wallemia produce the mycotoxins walleminol and walleminon and may cause subcutaneous infections and allergic reactions (farmer’s lung disease) in humans.
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Polona Zalar, G. Sybren de Hoog, Hans-Josef Schroers, John Michael Frank and Nina Gunde-Cimerman (2005). Taxonomy and phylogeny of the xerophilic genus Wallemia (Wallemiomycetes and Wallemiales, cl. et ord. nov.). Antonie van Leeuwenhoek (2005) 87:311–328.
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