Oxidative Weathering and Microbial Diversity of an Inactive Seafloor Hydrothermal Sulfide Chimney.

Jiangtao Li,Guojie Cui,Jiamei Cui,Huaiyang Zhou,Bingbing Wei,Yong Wang,Qunhui Yang,Zijun Wu

doi:10.3389/fmicb.2017.01378

Abstract

When its hydrothermal supply ceases, hydrothermal sulfide chimneys become inactive and commonly experience oxidative weathering on the seafloor. However, little is known about the oxidative weathering of inactive sulfide chimneys, nor about associated microbial community structures and their succession during this weathering process. In this work, an inactive sulfide chimney and a young chimney in the early sulfate stage of formation were collected from the Main Endeavor Field of the Juan de Fuca Ridge. To assess oxidative weathering, the ultrastructures of secondary alteration products accumulating on the chimney surface were examined and the presence of possible Fe-oxidizing bacteria (FeOB) was investigated. The results of ultrastructure observation revealed that FeOB-associated ultrastructures with indicative morphologies were abundantly present. Iron oxidizers primarily consisted of members closely related to Gallionella spp. and Mariprofundus spp., indicating Fe-oxidizing species likely promote the oxidative weathering of inactive sulfide chimneys. Abiotic accumulation of Fe-rich substances further indicates that oxidative weathering is a complex, dynamic process, alternately controlled by FeOB and by abiotic oxidization. Although hydrothermal fluid flow had ceased, inactive chimneys still accommodate an abundant and diverse microbiome whose microbial composition and metabolic potential dramatically differ from their counterparts at active vents. Bacterial lineages within current inactive chimney are dominated by members of α-, δ-, and γ-Proteobacteria and they are deduced to be closely involved in a diverse set of geochemical processes including iron oxidation, nitrogen fixation, ammonia oxidation and denitrification. At last, by examining microbial communities within hydrothermal chimneys at different formation stages, a general microbial community succession can be deduced from early formation stages of a sulfate chimney to actively mature sulfide structures, and then to the final inactive altered sulfide chimney. Our findings provide valuable insights into the microbe-involved oxidative weathering process and into microbial succession occurring at inactive hydrothermal sulfide chimney after high-temperature hydrothermal fluids have ceased venting.

Highlights

Hydrothermal sulfide chimneys, typical products of seafloor hydrothermal activity, encompass a variety of complex and dynamic environments where hot, reductive hydrothermal fluid interacts with cold, oxygenated seawater
It was inferred from X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) analyses that JDF1, derived from yellowish substrates of the outermost surfaces of inactive chimney walls, mainly consisted of amorphous Fe oxyhydroxides
XRD recognizable minerals in JDF1 most likely came from the underlying mineral assemblages when we scratched the thin surfaces to sample (Figure 1)

Summary

Introduction

Hydrothermal sulfide chimneys, typical products of seafloor hydrothermal activity, encompass a variety of complex and dynamic environments where hot, reductive hydrothermal fluid interacts with cold, oxygenated seawater. As one of the most productive ecosystems on Earth (Polz and Cavanaugh, 1995), active sulfide chimneys accommodate numerous unique microbial populations that obtain primary metabolic energy via chemosynthesis using a series of reactions made possible by the presence of intense chemical disequilibria between hydrothermal fluid and seawater. Sylvan et al (2012) revealed that a clear shift occurs from the dominant ε-Proteobacteria and Aquificae in active sulfides to bacterial communities dominated by α-, β-, γ-, δ-Proteobacteria and Bacteroidetes in inactive hydrothermal sulfides, indicating that inactive chimneys are remarkably distinct microbial habitats. Compared with numerous explorations of active hydrothermal structures, there have been few studies focusing on inactive chimneys and the process of microbial succession after active venting ceases. It has been suggested that minerals of inactive chimneys serve as critical energy sources to support the metabolic growth of various chemolithoautotrophs (McCollom, 2000; Edwards et al, 2003a), little is known about the extent to which microbial communities associated with quiescent chimneys continue to utilize those energy sources

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Conclusion