Hells Bells speleothems - Microbial ecology of cenote El Zapote

Extraordinary, subaqueous bell-shaped calcite formations, so-called Hells Bells, were discovered in the cenote El Zapote in southeastern Mexico. This study focused on the central question of whether microbial metabolic activity is significantly involved in the subaqueous growth of Hells Bells speleothems. Therefore, the microbial diversity was analyzed throughout the complex water column of the cenote, which comprises a freshwater zone, a redoxcline and a halocline that turns into saltwater in the deeper part of the cenote. Additionally, we aimed on the identification of the microbial key players and their metabolic activity in the redoxcline, a 1-2 m thick zone of steep counter-gradients of oxidized and reduced chemical species where the speleothems still grow. The microbial diversity of the different sub-biotopes of El Zapote was determined via 16S rRNA-based amplicon sequencing. For the microbial community in the redoxcline, a metagenomic and -transcriptomic profiling was conducted.