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 to damage archive collection materials. Understanding how mould grows and spreads is crucial for understanding 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. 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 indoor settings.
How Mould Grows
Moulds are decomposers, which means they break down organic matter such as dead plants, animals, and other organic materials. They do this by releasing enzymes to break down organic compounds into simpler forms.
Moulds grow through the repeated cell division , which creates long and branching chains. As these chains continue to grow and intertwine, they form a network of threads known as a mycelium. This mycelium extends through whatever material the mould is growing on , enabling it to extract nutrients efficiently.
How Mould Spreads
Some 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.
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.
Active, Dormant and Dead Mould
Moulds can exist in three states: active, inactive 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 biology 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 in relation to the deterioration of collection materials:
Mould Food Sources
Moulds can attack collection materials in two ways: opportunistic moulds that grow when suitable conditions and surfaces are available, and ’material pathogens‘ that specifically target certain surfaces. This means that some mould species are generalists, while others have a preference for specific materials.
Approximately 180 known species of mould have a preference for consuming materials made from, or containing, cellulose. A major component of paper, cellulose provides a valuable source of nutrients for these moulds.
Moulds gain the energy required for growth and reproduction by digesting paper components with the aid of enzymes. Small molecules can be digested by the moulds as they break down cell walls.
Mould and Water
When moulds attacks 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, denoted by a moisture meter, measures the amount of water available for supporting microbial 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 growth on collection materials.
Visible Effects of Mould
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 substances released by the mould as a result of its metabolism may chemically react with the paper, producing a noticeable colour change.
The visible mycelium 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 biology 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 deterioration.