Biochemical reactions and mechanisms involved in the biodeterioration of stone world cultural heritage under the tropical climate conditions

The World Cultural Heritage stone monuments/temples suffer from severe deterioration from weathering caused by a combination of physical, chemical and biological forces. Current knowledge on biodeterioration of these stone monuments has been improving because of the suite of research techniques available. Previous investigations were mainly carried out with culture-dependent methods to isolate and describe a small number of microorganisms from selective sites. Now, the culture-independent method of Next Generation Sequencing technologies is readily available at an affordable cost to obtain a much more deeper information of the microbial community of many sites more quickly. Since flora, fauna and microorganisms are members of the complex community on stone monuments in tropical regions, the fundamental scientific question remains to be the biochemical mechanisms involved for the destruction to allow a better and fundamental understanding of the interactions between the inorganic materials and the colonizing biota. More importantly, the biochemical processes shall be given more attention under the local environmental conditions, especially the tropical climate. Organic acids and inorganic acids (sulfuric and nitric), produced by colonizing biota are known biochemical processes and mechanisms contributing to the attack of stone. Lichens, cyanobacteria, fungi and bacteria are ubiquitously detected on surfaces of stone monuments of Angkor, Maya and Inca. Sulfur cycle and the oxidation are known major contributing factor to the destruction of stone. Recently, ammonia-oxidizing archaea are found more abundant than ammonia-oxidizing bacteria on the Angkor monuments in Cambodia. In addition, the mobility of solutes into and out of the stone is also involved to the damage of sandstone under the influence of water regime and climate conditions. The available information on the specific biochemical mechanisms by the microbiota on stone provides important insights into the biochemical reactions involved and also the protective measures against biodeterioration of the world cultural heritage effectively.