AIC's 44th Annual Meeting

The temples of Angkor monuments including Angkor Thom and Bayon in Cambodia and surrounding countries were constructed with sandstone exclusively. They show severely deterioration caused by physical, chemical and biological processes and, among them, the active growth of microorganisms on the sandstone surfaces leading to biodeterioration cannot be ignored, but knowledge on the microbial community and composition of the biofilms on the sandstone is not available from this region. This study investigated the microbial community diversity by examining the fresh and old microbial biofilms of the sandstone bas-relief wall surfaces of the Bayon Temple by analysis of 16S and 18S rRNA gene-PCR amplified sequences. A comparison of the microbial communities between the fresh and old biofilms showed that the bacterial community of old and fresh biofilms was very similar, but the eukaryotic communities were distinctly different between them. This information illustrates the dynamic formation and succession of microbial communities on sandstone in tropic region. Because biofilms are detrimental to the bas-reliefs engraved on the surface of sandstone, information about the microbial community is indispensable to control biofilm colonization. Non-destructive sampling of biofilm revealed novel bacterial groups of predominantly Rubrobacter in salmon pink biofilm, Cyanobacteria in chrome green biofilm, Cyanobacteria and Chloroflexi in signal violet biofilm, Chloroflexi in black gray biofilm, and Deinococcus-Thermus, Cyanobacteria, and Rubrobacter in blue green biofilm. Serial peeling-off of a thick biofilm by layers over depths with adhesive sheets revealed a stratified structure: the blue–green biofilm associated with serious deterioration was very rich in Cyanobacteria near the surface and Chloroflexi in deep layer below. Nitrate ion concentrations were high in the blue–green biofilm. The characteristic distribution of bacteria at different biofilm depths provides valuable information on not only the biofilm formation process but also the sandstone weathering process in the tropics. Ammonia-oxidizing archaea (AOA) amoA gene was amplified and investigated from Bayon temple, Angkor Thom. The results confirmed the detection of three large clusters, namely the Soil/sediment, the Nitrososphaera gargensis, and the Water column/sediment. Our sequences obtained fell into all three clusters and most of the clones were in the Soil/sediment cluster. The diversity of AOA amoA gene in Bayon, Cambodia was relatively high, indicating their contribution to production of nitrate from ammonia. AOB amoA gene-based PCR primer failed to generate any target DNA fragment bands after PCR amplification. AOB 16S rRNA gene was then introduced to amplify and detect AOB existence and abundance, but no AOB species were detected. AOB in all of the three samples from Bayon were below the detection limits. The information collective suggest that microorganisms are widely present on surface of sandstone temples and they are responsible for the different colors on surface; their activity is responsible for biodeterioration through nutrient cycling.