The active microbes and biochemical processes contributing to deterioration of Angkor sandstone monuments under the tropical climate in Cambodia – A review

•Available water is an important factor for microbial biofilm and protection of Angkor monuments.•The active microbes and the metabolic processes are foci of research and protection.•Biochemical processes of nitrogen and sulfur cycles are fundamental to the understanding biodeterioration.•Sulfur and ammonia oxidizing organisms can be used as indicators for warning.