Bacterial Communities from Deep Hydrothermal Systems: The Southern Gulf of California as an Example of Primeval Environments

Abstract

Deep hydrothermal systems result from the magmatic and tectonic activity of the ocean floor. This deep extreme biosphere represents a unique oasis of life driven by sulfur-based chemosynthesis instead of photosynthesis. The organisms inhabiting these systems are adapted to cope with harsh environmental conditions such as the absence of sunlight, high temperatures and hydrostatic pressures, and elevated concentrations of hydrogen sulfide, as well as high concentrations of heavy metals. Therefore, this biome is different from any other environment on modern Earth. As expected from such conditions, chemoautotrophic prokaryotes are the leading primary producers at the base of the food web considered as an analog to the oldest signs of life on Earth. Herein, we discuss prokaryotic diversity and community structure from the newly discovered hydrothermal systems in the Alarcón Rise (AR), the Pescadero Basin (PB), and the Pescadero Transform Fault (PTF) at the mouth of the Gulf of California, Mexico, using 16S rRNA gene amplicon Illumina sequencing. Despite the spatial proximity of the studied vent systems (<100 km), they differ considerably in their physical, chemical, geological settings, and biotic characteristics. Our results indicated that beta prokaryotic diversity is associated to the sampling source, suggesting a strong effect of environmental conditions in shaping microbial distribution. The most abundant phyla were Proteobacteria, Bacteroidetes, Actinobacteria, Chloroflexi, and Epsilonbacteraeota. Also, we found evidence on the oxidation of methane as a prevalent process in PB and PTF, since methylotrophic bacteria and Atribacteria were abundant, in contrast to AR basalt-hosted system. Bacteria associated with the sulfur cycle, in particular sulfur compounds reducing and sulfur compounds oxidizing bacteria predominated in all samples, confirming the importance of sulfur supporting vent communities. It is possible that vent systems played a significant role in the origins of life on Earth. Hence, they represent useful models when searching for life elsewhere in the universe.