Biodeterioration of archaeological sites and historic buildings is a major concern for conservators, archaeologists, and scientists involved in preservation of the world's cultural heritage. The Maya archaeological sites in southern Mexico, some of the most important cultural artifacts in the Western Hemisphere, are constructed of limestone. High temperature and humidity have resulted in substantial microbial growth on stone surfaces at many of the sites. Despite the porous nature of limestone and the common occurrence of endolithic microorganisms in many habitats, little is known about the microbial flora living inside the stone. We found a large endolithic bacterial community in limestone from the interior of the Maya archaeological site Ek' Balam. Analysis of 16S rDNA clones demonstrated disparate communities (endolithic: >80% Actinobacteria, Acidobacteria, and Low GC Firmicutes; epilithic: >50% Proteobacteria). The presence of differing epilithic and endolithic bacterial communities may be a significant factor for conservation of stone cultural heritage materials and quantitative prediction of carbonate weathering.

Force-volume microscopy (FVM) was used to study the interfacial and adhesive forces affecting primary bacterial attachment to surfaces. Forces were measured for titanium surfaces immersed either in cation-enriched (CE) solutions of yeast extract amended with phosphate buffer or in control solutions lacking the cation enrichment. The FVM measurements demonstrated that regions of elevated interfacial repulsion covered 72(±2)% of the surfaces immersed in CE solutions, compared to 26(±2)% for immersion in control solutions. Parallel collection of scanning electron micrographs demonstrated that surface densities of attached Pseudomonas aeruginosa were approximately 0.62(±1.3)×10 6 cells cm −2 compared to 8.7(±0.8)×10 6 cells cm −2 for surfaces immersed in the CE and control solutions, respectively. Interfacial repulsion indicated by FVM measurements therefore served as a predictor of bacterial attachment. Another factor influencing bacterial attachment was the adhesion force. FVM measurements indicated that the upper fifth percentile of surface adhesion was 1784(±40) pN for surfaces immersed in the CE solution compared to 2284(±40) pN for the control solutions. The more extensive regions of elevated interfacial repulsion as well as of decreased surface adhesion provide an explanation for the lower density of attached cells observed for the surfaces immersed in the CE compared to the control solutions. The conclusion is that FVM is a sensitive and informative technique that can be used to measure and explain interactions between microorganisms and surfaces.