Hyperthermophilic Anaerobic Nitrate-Dependent Fe(II) Oxidization by Tibetan Hot Spring Microbiota and the Formation of Fe Minerals

Abstract

Fe(II) in geothermal fluids was among the most important electron and energy sources for extremophiles and early life, and microbial oxidation of Fe(II) in turn contributed to the global Fe deposits such as banded iron formation (BIF). However, information was rare on Fe(II) bio-oxidation and consequent mineral formation in geothermal systems. In the present study, we investigated the anaerobic nitrate-depending Fe(II) oxidation (ANDFO) in the Tibetan hot springs with temperature ranging 52–86°C. ANDFO cultivation was established by inoculating sediments from the studied hot springs. Positive ANDFO reaction was observed in the cultures from three high-temperature hot springs (>80°C). Phylogenetic analysis showed that bacteria in the three obtained ANDFO cultures were mainly affiliated with phyla of Betaproteobacteria, Alphaproteobacteria, and Firmicutes. In the obtained ANDFO cultures, ferrous iron oxidation occurred with nitrate reduction, accompanied with the formation of magnetite and/or siderite, which could be finished within one week. The resulting euhedral magnetite was at the micrometer scale, which was larger in size and showed better crystallinity than its counterparts (usually <1 µm) formed by chemical reactions. Thus, it can be concluded that ANDFO bacteria and denitrifiers played important roles in the magnetite and siderite precipitation in the studied Tibetan hot springs. The coupling between Fe(II) oxidation and nitrate reduction mediated by thermophiles might provide a new mechanism for euhedral magnetite and siderite deposition in BIFs during the Precambrian period.

Keywords:

• Anaerobic nitrate-dependent Fe(II)-oxidation (ANDFO)
• BIFs
• hot springs
• magnetite
• Tibetan Plateau

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Special Foundation for Basic Research Program of China Ministry of Science & Technology (MOST) (No. 2015FY110100), the National Natural Science Foundation of China (Nos. 41422208, 41502318, and 41521001), the Key Project of International Cooperation of China Ministry of Science and Technology (No. 2013DFA31980), the 111 Program (State Administration of Foreign Experts Affairs & the Ministry of Education of China, Grant B18049), the cooperation foundation from Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, CAS (KLMM20170101), and the Fundamental Research Funds for the China Central Universities, China University of Geosciences (Wuhan).