Bacterial Populations (First Record) at Two Shallow Hydrothermal Vents of the Mexican Pacific West Coast

Abstract

Thermophilic and metal-oxidizing bacteria were identified in shallow hydrothermal vents on the western Mexican coast. The role of these bacteria in biomineralization processes observed in the vents is explained, and the effect of the vents on biodiversity of prokaryotes is discussed. Research was done at two shallow hydrothermal vent sites: Bahía Concepción (BC) in the Baja California Peninsula and Punta Mita (PM), on the central Pacific coast. Temperature at the sediments proximal to the vents was similar, but the redox potentials (0.5 V in BC and −0.3 V in PM) and pH (6.2 in BC and as low as 4.5 in PM) differed. The composition of the discharged water ranged from nearly seawater to lower-salinity fluids, and the gas phase was mainly CO₂ at BC and N₂ and CH₄ at PM. The study focuses on the biogeochemical processes related to the different species of bacteria present in the studied sites, which are involved in the anaerobic oxidation of methane (AOM), seawater sulfate reduction, and metal oxidation. The detected bacterial lineages represented typical deep vent species, which disproves a previous hypothesis that proposed that different consortia were populating deep and shallow hydrothermal vents. The results obtained here show that the main parameter affecting the bacterial groups present in shallow vents was the redox potential: gamma-, delta-, and epsilon proteobacteria as well as Bacteriodetes are present under the oxidizing conditions of BC, and Thermotogae, Aquificae, and Planctomycetes are present in PM. Sunlight abundance favored the prevalence of halophilic and Chlorofleaxae bacteria in both areas.

Keywords:

• marine sediments
• phylogenetic analysis
• shallow hydrothermal vent ecology

Acknowledgments

The development of this work would have not been possible without the valuable assistance of Ana Lilia Tirado-Chamú in sample processing. The authors are indebted to one anonymous reviewer, whose suggestions greatly improved the manuscript.

Funding

Funding was provided by the projects FONCICYT 94482 and IMPULSA IV. Additional support was provided by RENIECYT CONACyT 2249 (Support for Comprehensive Training PhDs in Science). Alejandro Estradas was supported by scholarships from the Earth Sciences−CONACyT graduate program and the project CONACyT 51127.