Abstract
Investigating the distribution of hydrogen-producing bacteria (HPB) is of great significance to understanding the source of biological hydrogen production in geothermal environments. Here, we explored the compositions of HPB populations in the sediments of hot springs from the Daggyai, Quzhuomu, Quseyongba, and Moluojiang geothermal zones on the Tibetan Plateau, with the use of Illumina MiSeq high-throughput sequencing of 16S rRNA genes and hydA genes. In the present study, the hydA genes were successfully amplified from the hot springs with a temperature of 46–87°C. The hydA gene phylogenetic analysis showed that the top three phyla of the HPB populations were Bacteroidetes (14.48%), Spirochaetes (14.12%), and Thermotogae (10.45%), while Proteobacteria were absent in the top 10 of the HPB populations, although Proteobacteria were dominant in the 16S rRNA gene sequences. Canonical correspondence analysis results indicate that the HPB community structure in the studied Tibetan hot springs was correlated with various environmental factors, such as temperature, pH, and elevation. The HPB community structure also showed a spatial distribution pattern; samples from the same area showed similar community structures. Furthermore, one HPB isolate affiliated with Firmicutes was obtained and demonstrated the capacity of hydrogen production. These results are important for us to understand the distribution and function of HPB in hot springs.
Highlights
Studying microbial distribution and function in geothermal environments is of great significance to the understanding of life evolution and the biogeochemical cycle of elements in high-temperature environments
For dissolved organic carbon (DOC) analysis, 25 ml of hot spring water was collected by a sterile 50-ml syringe and filtered through pre-combusted (450◦C, 4 h) GF/F filters (0.7-mm pore size, Whatman, Buckinghamshire, United Kingdom), and the resulting filtrate was collected into pre-combusted brown glass bottles with the addition of concentrated phosphoric acid [final concentration 0.2% (v/v)]
The hydrogen-producing bacteria (HPB) populations in the Tibetan hot spring samples were mainly composed of species affiliated with Bacteroidetes and Spirochaetales, similar to the dominant species in neutral high-temperature oil wells (Liu et al, 2016), but different from the dominant species in acidic hot springs in Yellowstone National Park (YNP) (Boyd et al, 2010)
Summary
Studying microbial distribution and function in geothermal environments is of great significance to the understanding of life evolution and the biogeochemical cycle of elements in high-temperature environments. Geothermal environments are characterized by high temperature, oligotrophic conditions, low dissolved oxygen, and high concentrations of hydrogen gas (Xu and Glansdorff, 2002; Konhauser et al, 2003; Zgonnik, 2020). Hydrogen can serve as one electron donor for microorganisms in geothermal environments (Lindsay et al, 2018; Gregory et al, 2019). The abiotic formation of hydrogen such as the interaction between water and crustal iron minerals has been reported in hydrothermal fluids (Lindsay et al, 2019). Less attention has been given to the biotic formation of hydrogen in geothermal environments
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