Etude de la diversité des algues et des cyanobactéries colonisant les revêtements de façade en France et recherche des facteurs favorisant leur implantation

Abstract : Building façades sometimes show green, red or blackish developments of biological origin. That kind of stainings create aesthetic damages of the building envelope and can induce, with time, a degradation of the colonised façade coating leading to high renovation costs. Biocide products incorporated into the coatings are actually a common way to fight against biological contamination. However, European regulations tend to restrict their use, which involves the need for development of effective and durable coatings, respecting the environment.
Microscopic algae and cyanobacteria forming façade biofilms are little known in France. So the first approach of this project consisted in sampling colonised façade coatings around France to identify constitutive micro-organisms. 22 algae species and 25 cyanobacteria species were identified in the 71 samples analysed, algae being dominant on all kinds of materials.
The factors favouring micro-organisms settlement and development were then investigated. A statistical treatment of environmental data gathered during the sampling campaign showed the importance of climatic factors leading to humidity on façades, factors favouring spores dissemination, as wind or vegetation proximity, as well as the importance of the nature of the colonised substrate. This last observation was deepened thanks to the use of a bench allowing simultaneous evaluation of different coating materials regarding their colonisation by algae and cyanobacteria strains isolated from façades. Factors such as porosity, roughness and surface pH of the materials showed to influence micro-organisms colonisation.
In parallel, in order to consider the development of materials disfavouring micro-organisms settlement, the adhesion mechanisms of a set of algae on model surfaces were investigated in a parallel plate flow chamber. The adhesion extent was weaker on hydrophilic surfaces. Experiments also showed that hydrophobic and electrostatic interactions were initiated during the adhesion process.
Finally, extracellular polymers produced by a selection of micro-organisms were analysed. They were of polysaccharide nature, anionic and more or less hydrophobic depending on the secreting strains. The adsorption of a polymer extracted from a strain of Klebsormidium flaccidum, the dominant alga on façades in France, was more important and stronger on hydrophobic surfaces rather than on hydrophilic ones. Furthermore, an enzymatic degradation of the same polymer tended to reduce the adhesion of K. flaccidum on hydrophobic surfaces. These observations confirmed the hypothesis by which extracellular polymers intervene during the contact phase of the micro-organism with the surface, and then during the adhesion consolidation, by initiating hydrophobic and probably electrostatic interactions.
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Submitted on : Sunday, November 18, 2007 - 3:05:47 PM
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Hélène Barberousse. Etude de la diversité des algues et des cyanobactéries colonisant les revêtements de façade en France et recherche des facteurs favorisant leur implantation. Ecologie, Environnement. Museum national d'histoire naturelle - MNHN PARIS, 2006. Français. ⟨tel-00188566⟩

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