Bacterial Composition of a Geothermal Site in Central Mexico

Abstract

Bacteria is the most diverse group of cellular organisms on earth. Next-generation gene sequencing technologies allow us to cost-effectively and accurately estimate the diversity of bacteria in multiple samples. Bacterial composition is affected by environmental conditions. Once these conditions are changed, complex bacterial populations will differ from the original composition for a long period of time, thus giving us a larger timeframe to identify environmental changes than water quality analysis alone. Here, we used 16s rRNA sequencing to identify the bacterial composition for two geothermal springs in the zone of Acoculco, Mexico during the rain and dry seasons of 2018. Overall, 91.8% of sequences were assigned at the Phylum level, 67.4% to genus and 30.8% to species. During both seasons, proteobacteria was the dominant phylum (Dry: 44%, Rain: 57%), followed by Firmicutes (Dry: 14%, Rain: 9%) and Actinobacteria (Dry: 11%, Rain: 9%). Cyanobacteria represented 11% of identified species during the dry season, but only 1% during the wet season. Four Phyla (Verrucomicrobia, Nitrospirae, Chlorobi and Thermosulfobacteria) were only found during the wet season. Physicochemical analysis indicates acid superficial waters with temperatures of 20.0 ºC to 31.8 ºC for Los Azufres springs, meanwhile, basic waters where found for La Alcaparroza with range of temperatures 18.0 ºC to 14.7 ºC. Dissolve oxygen were slightly different between ponds and seasons from both geothermal springs, meanwhile, total dissolve salt and conductivity different between seasons and springs. As result of a high bacterial activities in spring waters, high content of nitrite and low concentration of phosphorus compounds were found. A total of 20 chemical elements were determinate in springs waters, high sulfur and iron content were found in Acoculco springs with ranges of 36.7 to 358 mg/L and 102.0 to 12110 mg/L respectively, representing an acid-sulfuric waters with iron clusters expressions. This result agrees with Tello-Hinojosa (1994), Rocha-Lopez (2006) and Viggiano-Guerra (2011) studies, were presence of pyrite rocks were dominant and acid-sulfuric waters where found in the Acoculco area.