''Aureobasidium pullulans'' is a ubiquitous and generalistic black, yeast-like fungus that can be found in different environments (e.g. soil, water, air and limestone). It is well known as a naturally occurring

epiphyte An epiphyte is an organism that grows on the surface of a plant and derives its moisture and nutrients from the air, rain, water (in marine environments) or from debris accumulating around it. The plants on which epiphytes grow are called phoroph ...

endophyte An endophyte is an endosymbiont, often a bacterium or fungus, that lives within a plant for at least part of its life cycle without causing apparent disease. Endophytes are ubiquitous and have been found in all species of plants studied to date; h ...

of a wide range of plant species (e.g.

apple An apple is an edible fruit produced by an apple tree (''Malus domestica''). Apple trees are cultivated worldwide and are the most widely grown species in the genus '' Malus''. The tree originated in Central Asia, where its wild ancest ...

grape A grape is a fruit, botanically a berry, of the deciduous woody vines of the flowering plant genus '' Vitis''. Grapes are a non- climacteric type of fruit, generally occurring in clusters. The cultivation of grapes began perhaps 8,000 years a ...

, cucumber, green beans, cabbage) without causing any symptoms of disease. ''A. pullulans'' has a high importance in

biotechnology Biotechnology is the integration of natural sciences and engineering sciences in order to achieve the application of organisms, cells, parts thereof and molecular analogues for products and services. The term ''biotechnology'' was first used ...

for the production of different enzymes, siderophores and pullulan. Furthermore, ''A. pullulans'' is used in biological control of plant diseases, especially storage diseases. Chronic human exposure to ''A. pullulans'' via humidifiers or air conditioners can lead to hypersensitivity pneumonitis (extrinsic allergic alveolitis) or " humidifier lung". This condition is characterized acutely by

dyspnea Shortness of breath (SOB), also medically known as dyspnea (in AmE) or dyspnoea (in BrE), is an uncomfortable feeling of not being able to breathe well enough. The American Thoracic Society defines it as "a subjective experience of breathing di ...

, cough, fever, chest infiltrates, and acute inflammatory reaction. The condition can also be chronic, and

lymphocyte A lymphocyte is a type of white blood cell (leukocyte) in the immune system of most vertebrates. Lymphocytes include natural killer cells (which function in cell-mediated, cytotoxic innate immunity), T cells (for cell-mediated, cytotoxic a ...

-mediated. The chronic condition is characterized radiographically by reticulonodular infiltrates in the lung, with apical sparing. The strains causing infections in humans were reclassified to '' A. melanogenum''. ''A. pullulans'' can be cultivated on

potato The potato is a starchy food, a tuber of the plant ''Solanum tuberosum'' and is a root vegetable native to the Americas. The plant is a perennial in the nightshade family Solanaceae. Wild potato species can be found from the southern Uni ...

dextrose Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, usin ...

agar Agar ( or ), or agar-agar, is a jelly-like substance consisting of polysaccharides obtained from the cell walls of some species of red algae, primarily from ogonori (''Gracilaria'') and "tengusa" (''Gelidiaceae''). As found in nature, agar i ...

, where it produces smooth, faint pink, yeast-like colonies covered with a slimy mass of spores. Older colonies change to black due to

chlamydospore A chlamydospore is the thick-walled large resting spore of several kinds of fungi, including Ascomycota such as '' Candida'', Basidiomycota such as '' Panus'', and various Mortierellales species. It is the life-stage which survives in unfavourable ...

production. Primary

conidia A conidium ( ; ), sometimes termed an asexual chlamydospore or chlamydoconidium (), is an asexual, non- motile spore of a fungus. The word ''conidium'' comes from the Ancient Greek word for dust, ('). They are also called mitospores due to t ...

are

hyaline A hyaline substance is one with a glassy appearance. The word is derived from el, ὑάλινος, translit=hyálinos, lit=transparent, and el, ὕαλος, translit=hýalos, lit=crystal, glass, label=none. Histopathology Hyaline cartilage is ...

, smooth, ellipsoidal, one-celled, and variable in shape and size; secondary conidia are smaller.

Conidiophores A conidium ( ; ), sometimes termed an asexual chlamydospore or chlamydoconidium (), is an asexual, non-motile spore of a fungus. The word ''conidium'' comes from the Ancient Greek word for dust, ('). They are also called mitospores due to ...

are undifferentiated,

intercalary Intercalation may refer to: *Intercalation (chemistry), insertion of a molecule (or ion) into layered solids such as graphite *Intercalation (timekeeping), insertion of a leap day, week or month into some calendar years to make the calendar follo ...

or terminal, or arising as short lateral branches. Endoconidia are produced in an intercalary cell and released into a neighboring empty cell.

Hypha A hypha (; ) is a long, branching, filamentous structure of a fungus, oomycete, or actinobacterium. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium. Structure A hypha consists of one or ...

e are hyaline, smooth, and thinwalled, with transverse

septa The Southeastern Pennsylvania Transportation Authority (SEPTA) is a regional public transportation authority that operates bus, rapid transit, commuter rail, light rail, and electric trolleybus services for nearly 4 million people in five c ...

. The fungus grows at 10–35 °C with optimum growth at 30 °C. ''A. pullulans'' is notable for its

phenotypic plasticity Phenotypic plasticity refers to some of the changes in an organism's behavior, morphology and physiology in response to a unique environment. Fundamental to the way in which organisms cope with environmental variation, phenotypic plasticity encompa ...

. Colony morphology may be affected by carbon source, colony age, temperature, light and substrate, with colonies ranging from homogeneous to sectored, yeast-like to filamentous growth, and from small to large. These changes, potentially influenced by

epigenetic In biology, epigenetics is the study of stable phenotypic changes (known as ''marks'') that do not involve alterations in the DNA sequence. The Greek prefix '' epi-'' ( "over, outside of, around") in ''epigenetics'' implies features that are ...

factors, and the particular developmental sequences that the colonies proceed through may be observed with the

naked eye Naked eye, also called bare eye or unaided eye, is the practice of engaging in visual perception unaided by a magnifying, light-collecting optical instrument, such as a telescope or microscope, or eye protection. Vision corrected to norma ...

. Besides these morphological plasticity ''A. pullulans'' is also adaptable to various stressful conditions: hypersaline, acidic and alkaline, cold, and oligotrophic. Therefore, it is considered to be polyextremotolerant. The morphology-based taxonomy of the species is complicated by the large morphological variability between strains and even within a single strain. Based on molecular analyses, four varieties of the species ''A. pullulans'' were recognised: var. ''pullulans'' from substrates with low water activity and the

phyllosphere In microbiology, the phyllosphere is the total above-ground surface of a plant when viewed as a habitat for microorganisms. The phyllosphere can be further subdivided into the caulosphere (stems), phylloplane (leaves), anthosphere (flowers), an ...

and a variety of other habitats; var. ''melanogenum ''from aquatic habitats; var. ''subglaciale'' from

glacial A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate betwe ...

habitats; and var. ''namibiae'', which was described on the basis of only one strain isolated from

dolomitic Dolomite () is an anhydrous carbonate mineral composed of calcium magnesium carbonate, ideally The term is also used for a sedimentary carbonate rock composed mostly of the mineral dolomite. An alternative name sometimes used for the dolomitic ...

marble Marble is a metamorphic rock composed of recrystallized carbonate minerals, most commonly calcite or dolomite. Marble is typically not foliated (layered), although there are exceptions. In geology, the term ''marble'' refers to metamorphose ...

Namibia Namibia (, ), officially the Republic of Namibia, is a country in Southern Africa. Its western border is the Atlantic Ocean. It shares land borders with Zambia and Angola to the north, Botswana to the east and South Africa to the south and ea ...

. However, when the genome sequences of these varieties became available, the differences between them were considered as too large to be accommodated in a single species. Therefore, the varieties were reclassified as new species: ''A. pullulans'', '' A. melanogenum'', '' A. subglaciale'', and '' A. namibiae''. The genome of ''A. pullulans'' ''s. str.'' contains large numbers of genes of gene families that can be linked to the nutritional versatility of the species and its stress tolerance. The genome also contains a homothallic mating-type locus. Further genome sequencing of fifty ''A. pullulans'' ''s. str.'' strains showed that the population of the species is homogeneous, with high levels of recombination and good dispersal. The species ''A. pullulans'' was thus recognised as a true generalist, able to inhabit a wide variety of habitats with no specialization to any of these habitats at the genomic level. Despite the presence in the genome of a putative mating locus, and the observation of high recombination rates, no sexual cycle has yet been reported in this organism. Due to the relatively recent redefinition of the species, most published work does not yet distinguish between the new species belonging to the previously recognised ''A. pullulans'' species complex. It is therefore not clear to what extent this knowledge is valid for ''A. pullulans'' ''s. str.'' and what should be attributed to the three new species. __NOTOC__

References

External links

Genome Page on Mycocosm
{{Taxonbar, from=Q147300 Fungi described in 1884 Yeasts Dothideales Nepenthes infauna Epiphytes Fungal plant pathogens and diseases Apple tree diseases Fungal grape diseases Vegetable diseases

See also

References

Further reading

External links