Convergent Community Assembly among Globally Separated Acidic Cave Biofilms

Area of Science:

• Microbial Ecology
• Biogeography
• Extremophile Biology

Background:

• Acidophilic microorganisms inhabit extreme environments, offering insights into geographic influences on microbial distribution.
• Snottites in sulfidic caves represent unique, isolated habitats for studying microbial community assembly.
• Previous research indicated geographic structuring of specific acidophile populations, like Acidithiobacillus.

Purpose of the Study:

• To investigate the structure and diversity of microbial communities in extremely acidic snottites.
• To understand the role of geography in the community assembly of acidophiles in isolated cave ecosystems.
• To explore colonization histories and dispersal limitations of extremophiles in subsurface environments.

Main Methods:

• Analysis of 26 snottite samples from four sulfidic caves in Italy and Mexico.
• Utilized 16S rRNA gene cloning for microbial community profiling.
• Employed fluorescence in situ hybridization (FISH) for cell enumeration and identification.

Main Results:

• All samples exhibited low biodiversity, dominated by sulfur-oxidizing bacteria (Acidithiobacillus).
• Archaea (Thermoplasmatales) and other bacteria (Acidimicrobium, Ferrimicrobium) were present in varying proportions.
• Microbial populations of the same genera showed significant genetic divergence (95-98% 16S rRNA similarity) between continents, suggesting distinct evolutionary trajectories.

Conclusions:

• Community assembly in these sulfidic caves is characterized by stochastic colonization from local sources, followed by strong environmental selection for acid tolerance.
• Dispersal restrictions play a crucial role in maintaining the divergence of microbial populations within and among caves.
• Geographic isolation significantly influences the biogeography and genetic diversity of extremophilic microbial communities in subsurface environments.