A pellicle (also Kahmpilz ) is a biofilm of microorganisms , the at border crossings of media (. Eg surfaces is water or stones) accumulating the air. It is mainly formed by yeasts ( cold yeast ) and oxygen-dependent bacteria , whereby they are also formed from several species together. Non-polar substances located on the cell surface are particularly suitable for attachment to a gas / liquid interface . Many bacteria that form dead skin have an apolar surface layer. Instead, other bacteria have filamentous appendages ( pili ) made up of proteins with an apolar surface.
In the past, mushrooms were also known as mycodérma (slimy skin). Historical names are Mycoderma reell , Mycoderma aceti ( mother of vinegar or vinegar kahm , also Ulvina aceti or Bacillus aceti ), Mycoderma cerevisiae ( beer pot fungus , also: Saccharomyces Mycoderma Rees ), Mycoderma vini ( wine mushroom or florist yeast ) and Candida mycoderma .
When attached to the interface with the air, living beings can favorably absorb both nutrients from the liquid and oxygen from the air for an oxidative energy metabolism . This is an advantage compared to living beings that hover or swim in a liquid and are surrounded by it: In their case, the speed of their energy metabolism is limited by the lower oxygen concentration in the liquid. This effect is used by the communities of the surface membrane in water, the Neuston and Pleuston .
In the aquarium hobby
In the aquarium hobby , scum skin is perceived as a nuisance because it prevents optimal gas exchange. The cause is often a high concentration of nutrients due to overcrowding in the tank or too much feed.
The formation of the scum skin can be prevented by strong surface movement, which tears the scum skin open and thus prevents a closed scum skin. The scum can also be soaked up with newspaper that is briefly placed on the surface of the water. It is better to install a surface skimmer that draws the surface water into a filter . The microorganisms of the skin then break down superfluous nutrients in the filter.
In the production of biotic vinegar
In biotic vinegar production, the ethanol from an aqueous, dilute ethanol solution (e.g. wine ) is oxidized to acetic acid by acetic acid bacteria with oxygen . There are several ways to make this process happen quickly. An old process that is rarely used today is the so-called Orleans process , in which wine is stored in open barrels that are only partially filled until the wine has turned into vinegar. At the wine / air interface, a skin of acetic acid bacteria forms because the conditions there are favorable for ethanol oxidation: ethanol and nutrients from below from the liquid phase, oxygen from above from the air. Some of the acetic acid bacteria secrete cellulose fibers and in this way a relatively solid blanket is formed. Scum skins or masses of acetic acid bacteria in the vinegar are called mother-of-vinegar .
In the wine-making can film-forming yeasts (in viticulture and comb yeast called) cause damage. Film-forming yeasts are aerobic yeasts , the alcohol and organic acids, that is components of the wine, metabolize. They can form at the interface between wine and air.
At most, the flor yeasts , which also form on the surface of the wine, are desirable .
- ↑ a b Mycodérma . In: Meyers Großes Konversations-Lexikon . 6th edition. Volume 14, Bibliographisches Institut, Leipzig / Vienna 1908, p. 337 .