Mould, a type of fungus, is an essential component of our natural environment. However, mould is often associated with negative connotations due to its potential biodeterioration and damage of archive collection materials. The understanding of the ecology of mould is crucial for understanding its role, how it grows and how it can impact our collections.
- Diversity of mould: Mould encompasses a diverse group of fungi, with over 100,000 known species, and many more yet to be identified. These species vary in form and structure, reproductive strategies, and ecological niches. The incredible diversity of mould species allows mould to inhabit multiple different environments. They can be found in virtually every habitat, including forests, soils, freshwater, marine environments, and even indoor settings.
- Heterotrophic nature and nutrient cycling: Moulds are heterotrophic organisms, meaning they lack chlorophyll and cannot derive energy from sunlight like plants do. Instead, they obtain their energy through alternative means, such as the decomposition of organic materials. Moulds are decomposers, which means they break down organic matter such as dead plants, animals, and other organic materials. To do this, they secrete enzymes from the tips of their threads called hyphae. These digestive enzymes break down complex organic compounds into simpler forms, releasing essential nutrients back into the ecosystem, which mould uses as food. This is known as nutrient cycling.
- Mould growth and mycelium formation: Moulds grow through the repeated division and elongation of their hyphae, creating long and branching chains. As the hyphae continue to grow and intertwine, they form a network of threads known as a mycelium. This mycelium extends through the substrate, enabling the mould to extract nutrients efficiently.
- Formation and dispersal of spores: Some hyphal branches of moulds extend above the substrate and produce specialised structures called spores. These spores have a protective coat that shields them from harsh environmental conditions. Their small size allows for easy dispersal, either through touch or diffusion. Spores act as the reproductive units of moulds, enabling them to colonise new habitats with fewer competing organisms.
- Reproduction and adaptability: Moulds primarily reproduce asexually, but certain species can also undergo sexual reproduction under suitable conditions. This adaptability allows moulds to employ various reproductive strategies, increasing their chances of survival and successful colonisation. Moulds have an impressive adaptability to a wide range of environmental conditions. They can tolerate extreme temperatures, pH levels, and moisture variations. This adaptability enables moulds to colonise diverse habitats and thrive in environments that are inhospitable to other organisms. It is this resilience that allows moulds to fulfil their ecological roles in decomposition, nutrient cycling, and symbiotic relationships.
- States of existence: Moulds can exist in three states: active, dormant, and dead. During the active state, mould colonies form and actively reproduce, utilising available resources. In the dormant state, growth-supporting conditions are unfavourable, leading to a temporary cessation of reproduction until suitable conditions return. Eventually, mould colonies reach the end of their lifespan, resulting in a dead state where they do not regenerate, even if conditions become favourable.
The ecology of mould is closely linked to the degradation of archive collection materials, such as paper and cellulose-based items. Understanding how moulds interact with these materials is crucial for preserving and protecting cultural heritage. These are the ecological aspects of mould related to the biodeterioration of collection materials:
- Opportunistic moulds and material pathogens: Moulds can attack collection materials in two ways: opportunistic moulds that grow when suitable conditions and substrates are available, and ‘material pathogens’ that specifically target certain substrates. This means that some mould species are generalists, while others have a preference for specific materials.
- Cellulosic material preference: Approximately 180 known species of mould have a preference for consuming cellulosic material. Cellulose, a major component of paper, provides a valuable source of nutrients for these moulds.
- Enzymatic digestion: Moulds gain the energy required for growth and reproduction through enzymatic digestion of paper components. Small molecules can be digested by the moulds by breaking down cell walls.
- Water accumulation and relative humidity (RH): When fungi attack paper, they can liberate water during the degradation process. As a result, a mould colony can accumulate enough water to support its growth independently of the surrounding relative humidity (RH). Therefore, high RH alone may not always be an accurate indicator of mould growth.
- Water activity (aW): Water activity, denoted by aW, measures the amount of free water an organism requires for growth and is expressed as a value between 0 and 1. Higher values indicate an increased likelihood of mould growth. Monitoring and controlling the water activity of the environment can help prevent mould proliferation on collection materials.
- Discolouration: Mould growth on paper can result in visible discolouration. This can occur in two ways: pigments produced by fungi may be absorbed into the paper, or the metabolic products of the fungi may chemically react with the paper, producing a noticeable colour change.
- Impact on paper structure: The visible mycelium, or fungal threads, that grow on the surface of a document do not tell the whole story. Moulds can penetrate the paper’s fibre structure by growing down into its depths, potentially causing structural damage that is not immediately visible.
Understanding the ecology of mould in relation to the degradation of collection materials is crucial for implementing effective preventive measures and conservation strategies. Maintaining proper environmental conditions, including controlling moisture levels and implementing appropriate storage and handling practices, can help mitigate the risk of mould growth and protect valuable cultural heritage materials from biodeterioration.