11.9
生物劣化
生物劣化とは、微生物、特に菌類によって引き起こされる材料の望ましくない変質を指し、有機基質(紙、木材、繊維)と無機質(石、漆喰、ガラス)の両方を損傷させます。非生物的腐敗とは異なり、生物劣化は物理的な破壊や化学的分解を引き起こす生物学的活動によって引き起こされます。
物理的な劣化は、菌糸が孔隙や亀裂、…
生物劣化とは、古代の紙、木材、石、骨などの材料が、特に菌類などの生物的活動によって引き起こされる望ましくない変化のことです。
真菌の生物劣化は物理的および化学的なメカニズムの両方を含みます。
物理的には、菌糸が基質物質に浸透し、定着し、バイオピット、亀裂、繊維分離、表面侵食を引き起こします。
化学的には、菌類はセルラーゼやリグニナーゼなどの酵素を分泌し、木材や紙の構造ポリマーをより単純な分子に分解し、それを吸収して食物として利用します。
骨のような鉱物豊富な化石では、菌類が放出する有機酸がpHを下げ、鉱物を溶かして二次クラストを形成し、物質を弱めます。
さらに、メラニンなどの真菌色素や鉱物副産物も素材に染色を加えます。
予防戦略は、真菌の成長を支える環境条件を最小限に抑えることに重点を置いています。
これには湿度や温度の管理、ほこりの蓄積減少、水への直接曝露の防止が含まれます。
抗真菌処理や抗菌コーティングでさらなる損傷を防ぐことができます。
View the full transcript and gain access to JoVE Core videos
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.