Taxonomy
''Wallemia sebi'' is currently recognized as a species of the genus '' Wallemia'', which is first introduced by Johan-Olsen in 1887 for a single species '' W.ichthyophaga'' Johan-Olsen. A large number of synonyms were used before it was classified in ''Wallemia'', including ''Torula epizoa'' Corda, ''Sporendonema epizoum'' Corda, ''Sporendonema sebi'' Fr., and ''Sporotrichum navale'' Joly. The most commonly used synonyms is ''S. sebi'', which was named to refer to the fact that the conidia areHistory
The earliest synonym of ''W. sebi'' recorded is ''Torula epizoa'' Corda, which is originated from salty meant in Belgium in 1829. In 1832, Fries synonymized ''Torula epizoa'' Corda as ''Sporendonema sebi'' that describe tasteless solid fat extracted from animal fat. ''Sporendonema sebi'' was commonly used in literatures until in 1977 when von Arx synonymized genus ''Sporendonema'' and '' Wallemia''. ''Wallemia sebi'' then becomes a popular ''Wallemia'' species and frequently cited in studies. Frank and Hess studies the ''Sporendonema epizoum'' (synonym of W. sebi) that grow on dried salted fish and suggested it to beMicromorphology
''Wallemia sebi'' has transparent hyphae, that are usually 1.5–2.5 µm wide, forming a compactGrowth media
''Wallemia sebi'' can grow slowly on specialized fungal media with low water activity without additional solutes. On agar, ''W. sebi'' forms small brown colonies with a fine velvety texture, that have long rows of spores that may round up and become free at maturity. The colonies usually can grow to 2-2.5 millimeters, and sometimes to 4 to 5 millimeters in diameter. ''Wallemia sebi'' typically grow on MEA, MY50G, W-4 and W-10 agar. On MEA, the ''W. sebi'' colonies grow to 3-6 millimeters in diameter. The colonies formed are usually compact and powdery, and are rust brown to purplish-brown in color. The punctiform colonies are typically spreading deeply into MEA agars. On MY50G, the colonies can grow up to 12 millimeters with yellowish-brown color. The powdery colonies are formed due to the strong sporulation. On W-4 agar, the colonies can grow to 4-8 micrometer in diameter. The exudates can be observed on W-10 agar and they are present as yellow droplets. The shape of colonies in all agars is typically domed with or without short marginal spreading area. The marginal area can be shaggy or irregular with white color or similar color as the colony.Genome
The genome of ''Wallemia sebi'' was published in 2012. After the redefinition of the species in 2015 it was discovered that the sequenced strain belongs to a new species, '' W. mellicola'', and not ''W. sebi''.Secondary metabolite and toxicity
''Wallemia sebi'' produces secondary metabolic compounds like walleminol, walleminone, wallemia A and C, and azasteroid UCA1064-B A newly conducted study also observes a light yellow oil-like metabolite that produced by ''W. sebi'' called wallimidione (1-benzylhexahydroimidazo ,5-alphapyridine-3,5-dione), and it might be the most toxic of all metabolic productions. The first toxic compound found in ''W. sebi'' was isolated and named walleminol A by Wood et al. in 1990 in their study on toxic metabolite of ''W. sebi''. They suggested that walleminol A causes toxic effects in range of in vitro systems such as mammalian cell lines, protozoa and brine shrimp. The toxin contains two hydroxyl groups, four methyl groups, and two or three ring structures in the molecule. TheImpact on food
''Wallemia sebi'' invade food with lowImpact on built environment
Building material
Fungal growth often need adequate temperatures, nutrient substances, and some level of moisture. The requirements may vary between species. Like other xerophilic fungi, ''Wallemia sebi'' would grow on surfaces that are damp rather than wet. Since the indoor environments that is suitable for human habitation often satisfy the growth requirement for ''W. sebi'', ''W.sebi'' would be observed in building wallpaper if the water activity is not controlled as low. The finishing material and moisture level of constructions is critical in terms of fungal growth prevention. Poor moisture control (e.g. fail to dry material in constructions) will result in the growth ofHouse dust
''Wallemia sebi'' is abundant in settled dust in home, it has been first reported in Japan by Sakamoto ''et al.'' in 1989. It was also detected in house dust in Canada, USA and western Europe. The potential of fungi in indoor sources to cause asthma is not well documented, but ''W. sebi'' is one of the indoor fungi that has been found to cause allergic sensitization.Health effect
The health effect of chronic exposure to airborne fungi in indoor environment is known to be associated with both allergens and inflammatory compounds. Exposure to ''Wallemia sebi'' is suspected to cause allergic sensitization. One study found twenty percent of children between age of 3 to 14 express IgE sensitization to ''W. sebi''. There are also reports suggest the increase the risk of respiratory symptoms, asthma exasperation, hypersensitivity pneumonitis, rhinosinusitis, bronchitis and respiratory infections associate the exposure of building and house fungi, including ''W.sebi''.References
{{Taxonbar, from=Q10719179 Wallemiales Fungi described in 1829