Structure and Diversity of the Bacterial Communities in the Acid and Thermophilic Crater-Lake of the Volcano El Chichon, Mexico

El Chichon is an active volcano located in the Chiapas Volcanic Arc characterized by high temperatures, low pH, and large heavy metal concentrations. High temperatures are known to affect microorganisms, so the bacterial community structure was investigated in crater-lake sediment at a 'low' 50 degrees C and a 'high' 92 degrees C by sequencing the 16S rRNA bacterial gene. Most metal concentrations, and bacterial richness, and diversity indexes were higher at 50 degrees C than at 92 degrees C. Fifteen phyla were found in the sediment at 50 degrees C dominated by Actinobacteria (33.1%), Proteobacteria (29.1%) and Acidobacteria (20.1%). Nine phyla dominated by Firmicutes (52.7%, mostly Alicyclobacillus and Sulfobacillus) and Proteobacteria (44.8%, mostly Bradyrhizobium, Methylobacterium, Sediminibacterium) were detected in the sediment at 92 degrees C. The predictive functional profiling indicated metabolic pathways related to amino acid metabolism, membrane transport, replication, and repair as the most important. It was found that although a large number of bacterial groups were well adapted to 92 degrees C, the higher temperature reduced strongly, the bacterial diversity and species richness in the El Chichon volcano crater-lake system, and altered the bacterial community structure and their functionality.