( a ) Close-up photo of a lichen . ( b ) Lichen on a tree trunk . ( c ) Lichen and moss on a tree . Figure 4 : Lichens on trees ( Source : Daniel & Nicholas , 2013 ).
Figure 5 : Cross section of foliose lichen ( Source : Lichen , n . d .).
obligate anaerobes found in environments that are low in oxygen , such as water and soil . The archaea related to the nitrogen cycle produces inorganic acid , which then damages heritage buildings ( Meng et al ., 2017 ).
Fungi can cause decay of heritage buildings through pigmentation and patterns of colonisation ( Sterflinger & Piñar , 2013 ). Wood decay fungi can be in one of three categories : soft rot , white and brown fungi . Details of the difference between these fungi types are shown in Figure 3 . Soft rot fungi secrete cellulase from their hyphae . This is an enzyme that breaks down cellulose in timber , causing the formation of microscopic cavities inside the timber . Most types of white rot fungi break down the lignin in wood while leaving the lighter-coloured cellulose untouched . This causes
the timber to become moist and soft , while its colour becomes white or yellow . Brown-rot fungi break down hemicellulose in timber , the by-product of which produces hydrogen peroxide ( H 2
O 2
) which in turn breaks down cellulose in timber . The small molecule size of H 2
O 2 causes it to diffuse rapidly through the timber , causing decay even in places where the fungal hyphae do not penetrate . The decay causes the timber to shrink and become brown , later cracking into roughly cubical pieces .
Despite looking like a plant , a lichen is a composite organism of algae or cyanobacteria and multiple fungi species . The vegetative part of a lichen , which causes it to look like a plant , is called a thallus . Pictures of lichen are shown in Figure 4 , while a cross-section of a foliose lichen is shown in Figure 5 . Biodeterioration caused by
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