More wide occurrence and dominance of ammonia-oxidizing archaea than bacteria at three Angkor sandstone temples of Bayon, Phnom Krom and Wat Athvea in Cambodia

- Cultural heritage in Southeast Asia suffers from severe damage due to multiple reasons.
- Acid production is an important process contributing to the deterioration of cultural heritage.
- Ammonia-oxidizing archaea were more abundant then bacteria on sandstone temples in tropical Asia.
- Protective measures should include inactivation of functional microbial groups in biofilms on sandstone.

The Angkor monuments of Khmer civilization in Cambodia are suffering from serious deterioration by physical and chemical mechanisms as well as biological attack. The objectives of this study were to analyze the community of ammonia-oxidizing microorganisms as a biodeteriogen and the environmental factors contributing to biodeterioration of these sandstone monuments. A total of 34 samples were taken from three different temples in Siem Reap of Cambodia, including Phnom Krom, Wat Athvea, and Bayon of Angkor Thom. Our results showed that ammonia-oxidizing archaea (AOA) were detectable in 30 samples of all three sites, while ammonia-oxidizing bacteria (AOB) were detected in only 10 samples by polymer-chain reaction (PCR) amplification of the ammonia monooxygenase subunit A gene, amoA. Community analysis by constructing AOA and AOB clone libraries of the amoA gene revealed that the AOA community composition were more complex than that of AOB and related to at least three groups, Nitrosopumilus sp. from Group I.1a, Nitrosotalea sp. from Group I.1a-associated, and Nitrosophaera sp. from Group I.1b. AOB sequences obtained from samples in this study were clustered with the Nitrosospira lineage. Besides the higher diversity of AOA than AOB observed, AOA were also detected much higher abundance than AOB in majority of the samples based on the quantitative real-time PCR analysis. AOA and AOB had positive correlation with the sample pH values among the environmental variables analyzed in this study. Acidity may interact with minerals causing dissolution and crystallization regulated through wet and drying cycle. Overall, AOA were the dominating members over AOB in the nitrifying community and may play an important role in the biodeterioration of the monument sandstones via nitrogen cycling.

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