Aspergillus sydowii - the boundaries of habitats
Habitats play a decisive role not only in mycology, but in biology as a whole, and more specifically in the field of ecology. A habitat describes the possible habitat of organisms with both essential and obligate characteristics. Habitats can be described in any number of specific ways - from broad distinctions such as terrestrial or aquatic, to detailed conditions for individual species such as pH value or oxygen availability.
The preferred habitat is always a result of the physiological characteristics of a species, in interaction with biotic and abiotic factors. This knowledge is used specifically in the interpretation of microbiological laboratory data: Escherichia coli, for example, is interpreted as a direct indication of fecal contamination due to its preferred occurrence in the intestinal tract of mammals.
A change of habitat with consequences
Aspergillus sydowii is an interesting case of a species that, triggered by a change of habitat, simultaneously assumes a different biological function/biological niche. In the terrestrial environment, Aspergillus sydowii is considered a saprophyte, i.e. a decomposer of complex organic substances. In the marine habitat, however, the species becomes a parasite of corals of the genus Gorgonia. The spores of Aspergillus sydowii are probably introduced from the terrestrial environment via soil erosion and reach the sea, where they can infect the algae. An infection is systemic and can lead to tissue degeneration and malfunctioning of the polyps, as well as the death of the adult coral.
Picture 1) Front of an Aspergillus sydowii pure culture on DG18 agar. Incubated for seven days at 25 °C. Morphological identification is usually based on the detection of the round heads and the characteristic Delft blue color. Some culture media manufacturers may add a slight brown tint to this color due to other trace elements. A small amount of aerial mycelium is formed in the center. The white ring around the colony is caused by immature spore carriers.
Picture 2) Front of an Aspergillus sydowii pure culture incubated for seven days on MEA agar. The colony has significantly more water available on MEA, which causes the grooves already described for Cladosporium to form in the agar (the withdrawal of water causes the agar to shrink and form grooves). Aspergillus sydowii forms typical exudate droplets on MEA agar, the exact composition of which can vary. Lipids and sugars as well as other secondary metabolites (e.g. mycotoxins) are deposited.
Industrial use: Enzyme production
In the industrial sector, Aspergillus sydowii is used among other things in the enzyme production of cellulases and xylanases, i.e. the components of wood. Both cellulose and xylose are complex organic carbon compounds whose decomposition provides a raw material for use in other biotechnological processes.
Taxonomy:
Aspergillus sydowii was first described by Bainier & Sartory in 1913 as Sterigmatocystis sydowii, but was given its current name by Thom & Church in 1926 as part of a re-evaluation of the genus Aspergillus (source mycobank.org as of 05.2025). In addition to the core species, three further variations are now known: var. achlamydosporus, var. agrae and var. major.
For a long time, the species Aspergillus sydowii, within the group of Aspergillus section Versicolores, which comprises up to 17 species, was considered the only species that could be reliably differentiated from the others on the basis of morphological data. The reason for this is the characteristic Delft blue of the mature conidiospores in combination with the amber-colored exudates. However, new physiological and molecular data from 2022 suggest that there are only four species within the Versicolores section. These include Aspergillus versicolor, Asp. creber, Asp. sydowii and Asp. subversicolor. Whether these can be better distinguished morphologically from each other still needs to be clarified. Above all, it must be sufficiently clarified what is possible in routine analysis and what would be theoretically feasible.
Routine analysis:
In routine analysis, the species Aspergillus sydowii is certainly one of the more pleasant fungi in laboratory work. The characteristic coloration in combination with the comparatively large heads and the clearly defined colony structure make identification possible even on heavily overgrown culture media (> 80 CFU/plate). It is astonishing that all representatives of the Versicolores section are able to assert themselves at least a little, even under high competitive pressure. Even under competitive pressure, e.g. from Trichoderma or Cladosporium, individual heads are often still visible. Nevertheless, the detection of individual heads is not sufficient for reliable species identification.
The mold species Aspergillus sydowii is distributed worldwide and has been detected to date in a variety of habitats and on a wide range of substrates. In addition to the indoor damage relevant here, this also includes food, medical equipment, hypersaline, marine and terrestrial habitats. But beware, detection is now often carried out using molecular methods, which, however, do not initially allow any conclusions to be drawn about how well a mold species can live in the respective environment.
Indoor relevance: Moisture as the key
However, Aspergillus sydowii does play an important and well-known role in the field of microbial indoor damage. With a described aW value of approx. 0.8, the species and also the entire Versicolores section is one of the classic moisture indicators in indoor spaces (mold guide from the Federal Environment Agency). This means that an increased detection of Aspergillus sydowii is often directly related to damp material. The aW value of 0.8 indicates that with a preferred relative humidity of 80%, the surface/material must not be dripping wet. Thanks to its highly airborne conidiospores, Aspergillus sydowii is one of the species regularly detected in both impaction samples and material samples. The frequent detection of Aspergillus sydowii in ventilation systems also indicates that the species has no problem with draughts.
Medical relevance
According to TRBA 460 (2016:07), the mold species Aspergillus sydowii is classified in biological risk group 1. However, TRBA 460 refers to a deviating risk for humans after organ donation, as well as a high allergenic potential. According to the Atlas of Clinical Fungi (4th Ed. 2020), Aspergillus sydowii is occasionally found in connection with a clinical prevalence. Infection of organs has been detected in very rare cases, especially in immunosuppressed people. Due to the immense spore production and their easy air mobility, allergic effects cannot be ruled out in the case of a large Aspergillus sydowii infestation.
Light microscope image
Light microscope image of Aspergillus sydowii at 400x magnification (plus subsequent digital magnification). A vesicle-bearing head can be seen (right in the picture) and a spore carrier with a reduced vesicle (slightly further left in the picture). The spore chains, some of which are very long, are distributed throughout the picture. These are very unstable structures that disintegrate quickly and their detection in microscopic samples can indicate a spore source in the immediate vicinity. Tip: In the case of a very heavy Aspergillus infestation, it may be worth taking two adhesive specimens from the same spot, as there is a risk that the first specimen will only have spores on the adhesive strip.4
Scanning electron microscope image
Scanning electron microscope image of Aspergillus sydowii sputtered with gold at approx. 2741x magnification. Scale bar and on the right of the image indicates 20µm. In the center of the image is the vesicle with biseriate phialides at the end of which the conidiospores are formed, but which are missing in the image shown due to the preparation. Significantly smaller above and typical for the section Aspergillus versicolores is a penicillium-like spore carrier without vesicles. Here, the phialides stand on a greatly reduced vesicle, so that it appears that this is completely missing. As a direct consequence, the entire spore carrier is significantly smaller and contains far fewer phialides.
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