Higher diversity and abundance of ammonia-oxidizing archaea than bacteria detected at the Bayon Temple of Angkor Thom in Cambodia

Abstract

Ammonia-oxidizing archaea (AOA) and bacteria (AOB) are two groups of the ammonia-oxidizing microorganisms responsible for conversion of ammonia to nitrite, producing acidity and damaging building materials, including valuable cultural heritage stone structures. In this study, the molecular biomarker of amoA gene of archaea and bacteria was applied in polymerase chain reaction (PCR) amplification and quantitative real-time (RT) PCR (qPCR) to detect the abundance of AOA and AOB at 4 locations (Pond, Entrance, Gallery and Central Tower) of Bayon temple at Angkor Thom, Cambodia. The results showed that both AOA and AOB were positively detected at all locations and the diversity index suggested that AOA were more diverse than AOB. Sequences of AOA were mainly distributed in Group I.1b and few clustered in Group I.1a and Group I.1a-associated, while AOB were all closely related to β-proteobacteria (Nitrosospira). Based on the qPCR results, AOA outnumbered AOB clearly, the gene copy numbers of AOA amoA gene ranged from 1.35 × 106 to 2.52 × 108 copies per gram of dry materials, while, in comparison, AOB amoA gene copy numbers from 6.54 × 105 to 4.52 × 106 copies per gram of dry materials. In addition, the abundance of amoA gene from galleries was the highest than other locations. At gallery section, gene abundance, NH4+ and NO3− agreed well with the intensity of biofilm development. Based on the community and abundance analysis, nitrogen cycling plays an important role in contributing to deterioration of sandstone monuments at Angkor Thom in Cambodia under tropical climate.