Unraveling of microbial colonizers driving biodeterioration divergence of brick heritage of the Nanjing Ming City Wall, a UNESCO World Heritage Site of China

Abstract

Historical buildings are an essential representative of UNESCO World Heritage, but they can also harbour microbial threats due to long-term exposure to an open environment. Given the dynamics of outdoor environmental parameters, microbial communities shape diverse functions that can lead to divergence in the biodeterioration of historical buildings, posing a significant challenge to heritage conservation. Here, we investigate the physicochemical characteristics of the biodeteriorated brick heritage of the Nanjing Ming City Wall, unravel the correlations between microbial communities and physicochemical parameters, and explore the key taxa that drive the biodeterioration divergence. Despite being sampled in the same area, physicochemical analysis indicated a significant divergence in the deterioration of the brick heritage. Microbial structures suggested that the predominant phyla are Acidobacteriota, Cyanobacteria, Gemmatimonadota, Proteobacteria, Chloroflexi, and Actinobacteriota, highlighting Acidobacteriota and Chloroflexi as the key players that shape the divergence in biodeterioration. Moreover, the correlations between microbial communities and physicochemical parameters confirmed that members of Acidobacteriota and Chloroflexi contribute to the biodeterioration divergence, probably through denitrification and nitrification. Given that the biodeteriorated bricks are situated in the same environment, we claim that the in-situ microenvironment that microbial colonizers might shape could, in turn, affect biodeterioration. Our findings will advance knowledge of the microbiomes that drive the biodeterioration dynamics of brick heritage and provide a basis for diagnosing microbial biodeterioration of outdoor stone heritage.