11.9
Biodétérioration
La biodétérioration fait référence à l’altération indésirable des matériaux causée par des micro-organismes — en particulier des champignons — qui end…
La biodétérioration est l’altération indésirable de matériaux — tels que les papiers anciens, le bois, la pierre et les os — causée par l’activité biologique des microbes, en particulier les champignons.
La biodétérioration fongique implique à la fois des mécanismes physiques et chimiques.
Physiquement, les hyphes fongiques pénètrent et colonisent le matériau du substrat, provoquant des biopits, des fissures, la séparation des fibres et l’érosion de la surface.
Chimiquement, les champignons sécrètent des enzymes telles que les cellulases et les ligninases qui dégradent les polymères structurels du bois ou du papier en molécules plus simples, qu’ils absorbent comme nourriture.
Sur les fossiles riches en minéraux, comme les os, les acides organiques libérés par les champignons abaissent le pH et dissolvent les minéraux pour former des croûtes secondaires, affaiblissant ainsi la matière.
De plus, des pigments fongiques, tels que les mélanines, ainsi que des sous-produits minéraux, colorent les matériaux.
Les stratégies préventives visent à minimiser les conditions environnementales favorisant la croissance fongique.
Cela inclut le contrôle de l’humidité et de la température, la réduction des dépôts de poussière et la prévention de l’exposition directe à l’eau.
Les traitements antifongiques ou les revêtements antimicrobiens protecteurs peuvent prévenir d’autres dommages.
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Q1: What causes biodeterioration of historical materials?
Biodeterioration is the undesirable alteration of materials like ancient papers, wood, stone, and bone caused by biological activity, especially fungi. Fungi damage materials through both physical mechanisms—such as hyphal penetration causing biopitting and fiber separation—and chemical mechanisms involving enzyme secretion and organic acid production that degrade structural polymers and dissolve minerals.
Q2: How do fungal enzymes break down organic materials?
Fungi secrete hydrolytic enzymes including cellulases and ligninases that degrade structural polymers in wood and paper into simpler molecules, which fungi then absorb as food. These enzymes break down cellulose, lignin, and other organic polymers, causing progressive weakening and decomposition of the substrate material.
Q3: What role do organic acids play in fungal biodeterioration?
Fungi excrete organic acids such as oxalic and citric acid that lower pH and dissolve minerals in bone and fossil materials. On mineral-rich substrates, these acids form secondary crusts and weaken structural integrity. Additionally, siderophores released by fungi solubilize metals, further altering the substrate composition and microbial ecology.
Q4: How do fungal biofilms enhance material deterioration?
Fungi commonly exist within biofilms containing bacteria, algae, or lichens that enhance microbial adhesion and protect organisms from environmental stress. These biofilms support cooperative metabolism, resulting in layered and progressive deterioration. The complex community structure accelerates both physical and chemical damage to substrates.
Q5: What environmental factors support fungal growth on materials?
High humidity, elevated temperature, dust buildup, and direct water exposure create conditions favoring fungal colonization. Preventive strategies focus on controlling these environmental factors to minimize biodeterioration. Reducing moisture and maintaining stable temperature are critical for protecting vulnerable materials from fungal attack.
Q6: How can antifungal treatments prevent biodeterioration?
Antifungal treatments and protective antimicrobial coatings prevent further fungal damage once colonization occurs. When biodeterioration is detected, identification via microscopy or DNA-based tools guides targeted antifungal applications. Combined with environmental control measures, these treatments help preserve historical and culturally significant materials.
Q7: What staining effects do fungal pigments cause on materials?
Fungal pigments such as melanins and quinones penetrate deeply into porous materials, causing often irreversible staining. These pigments, along with mineral byproducts from fungal metabolism, discolor substrates. Biomineralization processes, where fungi precipitate minerals like calcium oxalate crusts, further contribute to visible damage and material weakening.