A Biofilm forms when certain microorganisms adhere to a surface in a moist environment and begin to reproduce.Biofilm formation on surfaces usually starts with phototrophic organisms (algae, cyanobacteria) which use carbon dioxide (CO2) from the atmosphere and sunlight as their carbon and energy source.
Heterotrophic organisms (most bacteria and all fungi) need some organic source for their growth, and this is provided by the metabolites of phototrophic organisms or by airborne deposition. The biofilm community is therefore sometimes formed by a single microbial species, but in nature biofilms almost always consist of mixtures of many species of bacteria, as well as fungi, algae, yeasts, protozoa, and other microorganisms, along with non-living debris and corrosion products.
All biofilm forming microorganisms may cause biodeterioration and degrade stone or render mechanically, chemically and aesthetically through the metabolic activities and biomineralization process in these biofilms.
It is apparent that some species, in particular pigment-producing fungi (Alternaria, Penicillium, Aspergillus), can lead to deterioration of appearance which, even after removal of the species itself, can be difficult to remove.
Other species such as algae and lichens are also very brightly coloured and can rapidly develop and spoil the appearance of surfaces
moss & lichen
Hence, the major period of concern for spread is limited the high sporulation period. Quaternary Ammonium Compounds (DDAC) are not effective at killing spores due to the spores having a thickened cell wall. However, as the spores begin to germinate, they produce protonema which are thread-like filaments which grow and colonise the substrate on which they have established.
The protonema have thin cell walls and it is at this stage that the DDAC is able to penetrate protonema and disrupt the cells, killing the organism prior to it becoming established on surfaces. In addition to the effectiveness against moss, AlgoClear® Pro is an extremely effective algaecide and will be effective at reducing these species colonising most surfaces.
The genus Trentepohlia would not, at first glance, be taken as a green alga. Free-living species are mostly yellow to bright orange or red-brown in colour, due to the orange pigment, haematochrome (β-carotene), which usually hides the green of the chlorophyll. The genus is terrestrial and is often found in Europe on rocks, walls and tree bark. Where they are found on buildings, they can cause severe mechanical degradation and deterioration.
Fabio Rindi and Michael D. Guiry (2002) have identified five species of the genera Trentepohlia and Printzina in urban habitats in Western Ireland: Trentepohlia abietina (Flotow) Hansgirg, T.aurea (Linnaeus) Martius, T. iolithus (Linnaeus) Wallroth, T.cf.umbrina (Kützing) Bornet, and Printzina lagenifera (Hildebrandt) Thompson et Wujek. These species formed perennial populations on a variety of substrata. Of the species identified, T.aurea and T.iolithus were found on old concrete and cement walls; in particular, the latter species formed characteristic, extensive, deep-red patches on many buildings.
Western Ireland is a cold temperate area with high levels of rainfall and humidity. This area therefore supports a high level of rich and diversified algal flora. Trentepholia have been identified as one of the most common species to be isolated from walls and buildings in this region (Rindi, Guiry 2002).