The diversity of microbes and prediction of their functions in karst caves under the influence of human tourism activities—a case study of Zhijin Cave in Southwest China

Abstract

Microorganisms, sensitive to the surrounding environment changes, show how the cave environment can be impacted by human activities. Zhijin Cave, featured with the most well-developed karst landform in China, has been open to tourists for more than 30 years. This study explored the microbial diversity in a karst cave and the impacts of tourism activities on the microbial communities and the community structures of bacteria and archaea in three niches in Zhijin Cave, including the mixture of bacteria and cyanobacteria on the rock wall, the aquatic sediments, and the surface sediments, using 16S rRNA high-throughput sequencing technology. It was found that Actinobacteriota and Proteobacteria were the dominant bacteria in the cave and Crenarchaeota and Thermoplasmatota were the dominant archaea. The correlation between microorganisms and environmental variables in the cave showed that archaea were more affected by pH and ORP than bacteria and F − , Cl − , NO 3 − , and SO 4 2− were all positively relevant to the distribution of most bacteria and archaea in the cave. PICRUSt's prediction of microbial functions also indicated that abundance of the bacteria's functions was higher than that of the archaea. The intention of this study was to improve the understanding, development, and protection of microbial resources in caves.

Archaea and their interactions with bacteria in a karst ecosystem

“…The proteins related to ATP binding, such as iron (III) transport system ATP-binding protein [EC: 3.6.3.30], branched-chain amino acid transport system ATP-binding protein, and putative spermidine/putrescine transport system ATP-binding protein, were dominant in DW samples (Figure 5C). Overall, Thaumarchaeota and Crenarchaeota were reported to be dominant in karst niches, such as weathered rocks, sediments within the cave and soils outside the cave (Ai et al, 2022), which were consistent with our results mainly dominated by Thaumarchaeota, with a relative abundance ranging from 0.23 ± 0.14% to 21.69 ± 8.88% (Figure 1D; Supplementary Table 2). Thaumarchaeota might associate with the acidic environment due to their dominance in the acidic cave with a pH value ranging from 4.97 to 6.88 (Barton et al, 2014).…”

“…The sediments in the dark zone of the Heshang Cave were covered with bat guano, the dominance of Euryarchaeota in our cave was consistent with previous studies. Simultaneously, high Shannon indices of archaea and bacteria were observed in the Heshang Cave ecosystem (Figures 1A,B) compared with the previous reports (Ai et al, 2022;Xiao et al, 2022). SD was dominant by Rokubacteria (24.22 ± 5.99%) and GAL15 (13.03 ± 4.29%) (Figure 1D, Supplementary Table 2).…”

Temperature and Moisture Gradients Drive the Shifts of the Bacterial Microbiomes in 1000-Year-Old Mausoleums

“…The exquisite frescoes are located in the back room of the Qinling Mausoleum, which attracted larger numbers of visitors to the back room due to interest in the frescoes. The difference may have been caused by the tourist activity [13,44,45]. Therefore, it can be assumed that the tourism-related activity could have promoted the shifts in the microbial community diversity in the back room of the Qinling Mausoleum.…”

“…In this study, a significant increase of Cyanobacteria was found in the back room of the Qinling Mausoleum. It should be noted that the colonized Cyanobacteria could cause aesthetic, physical and chemical damages to historical relics [19,44,51]. Fourthly, inspiration from numerous visitors has raised the CO 2 concentration levels inside the tomb [44,54], intensifying the corrosion of the walls and facilitating microbial proliferation that could accelerate biodeterioration [49,55].…”

“…It should be noted that the colonized Cyanobacteria could cause aesthetic, physical and chemical damages to historical relics [19,44,51]. Fourthly, inspiration from numerous visitors has raised the CO 2 concentration levels inside the tomb [44,54], intensifying the corrosion of the walls and facilitating microbial proliferation that could accelerate biodeterioration [49,55]. Therefore, although the development and involvement of cultural relics in the tourism industry is beneficial for the local economy, tourism-related activity could bring additional 'non-native' microbial resources that may inevitably damage the 'skins' of the ancient relics due to their uniqueness in the area's metabolic habits.…”