Five-Year Monitoring of Bacterial Communities in Dripping Water from the Heshang Cave in Central China: Implication for Paleoclimate Reconstruction and Ecological Functions

Abstract

Microbial lipids in stalagmites are increasingly used to reconstruct the paleoclimate change, necessitating the investigations on microbial communities in dripping waters. A pilot molecular survey was conducted on bacterial communities of dripping waters at two sites (1D and 3D) in Heshang Cave of Hubei province in central China for a period of 2008 to 2013. The samples were subjected to genome DNA extraction, 16S rRNA gene amplification, clone library construction and phylogenetic analysis to explore the seasonal variation of bacterial communities and their association with environmental factors including regional air temperature， precipitation, cave temperature, pH, conductivity and dripping rate of the water samples. Seasonal variations were clearly observed in components and diversities of bacterial communities at both sites. Bacterial community was dominated by Gammaproteobacteria in autumn and winter, whereasDownloaded by [FU Berlin] at 04:42 04 July 2015 ACCEPTED MANUSCRIPT ACCEPTED MANUSCRIPT 2Betaproteobacteria became dominant in samples collected in summer and spring. Among the environmental factors investigated, regional air temperature was found to have a strong impact on bacterial communities indicated by cluster and redundancy analysis. Moreover the bacterial biodiversity was observed to increase with the temperature rising. Bacteria identified in dripping water were either oligotrophs or able to acquire nutrients from minerals under oligotrophic conditions. They may also be able to induce calcite precipitation in cave systems. Our data shed light on the potential of microbes used as a tool for the reconstruction of paleo-temperature as well as on the ecological functions of bacterial communities in oligotrophic caves.

The Relationship between pH and Bacterial Communities in a Single Karst Ecosystem and Its Implication for Soil Acidification

“…Actinobacteria dominated the weathered cave wall communities in Heshang Cave, and this phylum is commonly found in cave environments, such as the weathered rocks of the Buda thermal Karst System (Borsodi et al, 2012), Grotta dei Cervi in Italy (Groth et al, 2001) and other cave walls (Mulec et al, 2012a,b). Proteobacteria, specifically Gammaproteobacteria and Betaproteobacteria, are the most abundant bacteria in the drip waters, including the ones in Heshang Cave (Yun et al, 2016). …”

“…The annual average temperature is ∼16.5°C and average annual rainfall is ∼1118 mm. Most of the precipitation (∼70%) occurs in April to September (Hu et al, 2008a; Yun et al, 2016). Vegetation consists of dense forests of subtropical tress and shrub, and corn and other vegetable crops are grown on the mountains.…”

“…DW3 was in the twilight zone, and DW1 and DW2 were in the dark zone ( Figure 1D ). Drip water samples were collected with 10 L sterile plastic bottles and sterile funnels, and the others were collected aseptically with 50 ml sterile plastic centrifuge tubes (Corning), as described previously (Yun et al, 2016). All samples were transported to the geomicrobiology laboratory in China University of Geosciences (Wuhan) under refrigeration within 24 h of collection.…”

“…pH of drip water was measured in situ with a multiparameter water quality detector (HACH, Loveland, CO, USA) (Yun et al, 2016). Solid samples were pre-frozen at -80°C for an hour and then freeze-dried (ALPHA 1-2 LD, Christ, Germany) for 48 h to remove water.…”

“…To test the hypothesis, we investigated the correlation between environmental factors, especially pH, and microbial communities in a full karst ecosystem, from the surface soils overlying the cave system and from various habitats within the cave, including epikarstic drip waters that link the surface to subsurface ( Figure 1B ). Although microbial communities have been separately investigated from drip waters in caves (Liu et al, 2010; Yun et al, 2016), cave sediments (Man et al, 2015; Wu et al, 2015), weathered rocks in caves (Ward et al, 2009; Man et al, 2015), soils overlying cave systems (Castro et al, 2010; Ortiz et al, 2014), and bat guano (Man et al, 2015), no systematic evaluation of the communities throughout a karst system has been conducted previously. The results from this study provide an assessment of bacterial communities in central China karst and reveal the potential consequence of acidification on bacterial community composition in the karst habitats.…”