The invasive fungi comprise Ascomycetes, Aspergillus, Penicillium, Chrysosporium, and Cladosporium etc. Some of these organisms form rusty-red spots and black layers. Also, fungi produce acids and enzyme that dissolve and degrade stones, wood, and canvas, as well as colouring pigments, oil binders, ink and glue.
Green algae, lichens, and cyanobacteria (Eucapsis, Scytonema, Leptolyngbya, and Fischerella) produce large dark green stains in a humid environment. Similarly to fungi, they release organic solvents that deteriorate museum artifacts.
Various bacteria (Bacillus, Pseudomonas, Staphylococcus, Micromonospora, and Virgibacillus) modify inorganic components, produce organic acids and enzymes that cause discolouration and lead to the formation of spots.