Abstract
The distribution and succession of microbial communities along the dispersion path of hydrothermal plumes has not been well investigated. In this study, we collected several types of samples from the Longqi hydrothermal field located on the Southwest Indian Ridge, including hydrothermal plumes at different stages of formation, a suite of water column samples across the non-buoyant hydrothermal plumes above this field, and a background seawater column approximately 350 km away from the hydrothermal field. Using CH4 concentration anomalies, three non-buoyant plume samples between 2,535 m and 2,735 m were identified within the water column. Microbial community compositions within these plumes and background seawater samples were examined based on the 16S rRNA genes and revealed significant variations and successions in community composition between different portions of the hydrothermal plumes. Near the vent orifice, representing the initial stage of plume formation, microbial populations were characterized by abundant and diverse putative vent-associated communities including (hyper)thermophiles such as Aquificaceae and Hydrogenothermaceae within the phylum Aquificae, and some epsilonproteobacterial chemolithoautotrophs such as Sulfurovum, Sulfurimonas, and Caminibacter. By contrast, in the rising buoyant plumes and adjacent seawaters, most vent-associated microbial taxa were still present but made only minor contributions to community composition. Some microbial taxa that are common in seawater columns such as alphaproteobacterial Sphingomonadaceae and SAR11 clade, deltaproteobacterial SAR324 clade, and gammaproteobacterial Pseudomonas, together with Sulfurimonas and SUP05 clade, became predominant. Members within the Sulfurimonas and SUP05 clade flourished with considerable abundance in the non-buoyant plumes, although these plumes were mainly composed of alphaproteobacterial Rhodobacteraceae, gammaproteobacterial Alteromonadaceae and Saccharospirillaceae putatively derived from the surrounding ambient seawater. We also analyzed archaeal components in the initial discharge and rising buoyant plume stages, with both primarily consisting of thaumarchaeal Nitrosopumilales and euryarchaeal Marine Group II. Our results indicated that being characteristic microbial lineages within the hydrothermal plumes of the Southwest Indian Ridge, both Sulfurimonas and SUP05 clade display a common and abundant distribution across the plume path. However, out of these clades, Sulfurimonas is more abundant and widespread.
Highlights
Hydrothermal plumes, the result of mixing of hot, anoxic hydrothermal fluid and cold, oxygenated seawater, commonly occur at mid-ocean ridges worldwide and exert an important influence on ocean chemistry and microbiology on a global scale (Elderfield and Schultz, 1996; Jackson et al, 2010; Anantharaman et al, 2016)
One ridge section is located between the Indomed and Gallieni transform faults of the Southwest Indian Ridge (SWIR) from 49◦E to 53◦E where six hydrothermal fields have been found, while the other section lies on the SWIR between the Melville transform fault and Rodriguez triple junction (RTJ) from 63◦E to 64◦E where two hydrothermal fields were discovered (Tao et al, 2012, 2014)
In addition to the non-buoyant plumes above Longqi vent field, members of Sulfurimonas and SUP05 clade were detected in the CTD01 water column samples (Figure 5) which we considered as normal background seawater, free of influence from hydrothermal activity
Summary
Hydrothermal plumes, the result of mixing of hot, anoxic hydrothermal fluid and cold, oxygenated seawater, commonly occur at mid-ocean ridges worldwide and exert an important influence on ocean chemistry and microbiology on a global scale (Elderfield and Schultz, 1996; Jackson et al, 2010; Anantharaman et al, 2016). Metagenomics analysis showed that oxidation of reduced sulfur species constitutes the most abundant and diverse chemolithotrophic energy metabolism in the Eastern Lau Spreading Center hydrothermal plumes (Anantharaman et al, 2016). These studies are insightful and microbiomes have received a great amount of attention in recent years, plume microbiology remains poorly understood. Hydrothermal plumes are widely distributed throughout the global mid-ocean ridge system, many of them are still unexplored from the perspective of microbiology, especially at ultraslow spreading ridges (German et al, 2010; Li J. et al, 2016)
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