Biodeterioration of limestone: role of bacterial biofilms and possible intervention strategies

<p>Limestone built heritage is at risk from the effects of biofilms, a microbial communityencapsulated in a matrix of sugars, protein and extracellular DNA. Although biofilm research hasbeen carried out in Mediterranean regions, few studies cover temperate Northern Europeclimates, or the UK. This study concentrates on bacterial colonisation of Lincoln limestone, ahighly vulnerable building material, and identifies the species, their role in biodeterioration andthe efficacy of biocides against them.As part of this study the core species which comprise the bacterial component of the limestonemicrobiome have been characterised for the first time; this has allowed the identification of noncore species which are significantly associated with damaged and undamaged surfaces.Four mechanisms of biodeterioration have been identified, one previously unidentified, andisolated species have been characterised as to whether they are biodeteriorative and themechanisms of biodeterioration that they employ. Two species, Curtobacterium flaccumfaciensand Solibacillus silvestris, have been characterised as producing biofilm matrix which activelycauses biomechanical damage to the oolitic limestone structure as opposed to the passiveenhancement of physical weathering which has been previously associated with biofilm matrix.Species capable of biodeterioration have also been shown to be present on both damaged andundamaged surfaces, something which has not been previously investigated.Environmental sampling, species identification and characterisation of species forbiodeterioration have all combined to identify markers of biodeterioration, ie both physicalmarkers and biomarkers. Specifically, a surface pH of 5.5 or lower and the presence of B.licheniformis is indicative of biodeterioration with a proportionally higher level of M. luteus whencomparing damaged and undamaged stone.Finally this study brings the literature on conservation methods up to date by testing biocideswhich are in current usage, as many biocides in the literature are discontinued. This study is alsothe first in the field to show their efficacy against biofilm encapsulated bacteria and theirpropensity for chemically disrupting the biofilm matrix.</p>