Hadal biosphere: Insight into the microbial ecosystem in the deepest ocean on Earth

Abstract

Hadal oceans at water depths below 6,000 m are the least-explored aquatic biosphere. The Challenger Deep, located in the western equatorial Pacific, with a water depth of ∼11 km, is the deepest ocean on Earth. Microbial communities associated with waters from the sea surface to the trench bottom (0 ∼10,257 m) in the Challenger Deep were analyzed, and unprecedented trench microbial communities were identified in the hadal waters (6,000 ∼10,257 m) that were distinct from the abyssal microbial communities. The potentially chemolithotrophic populations were less abundant in the hadal water than those in the upper abyssal waters. The emerging members of chemolithotrophic nitrifiers in the hadal water that likely adapt to the higher flux of electron donors were also different from those in the abyssal waters that adapt to the lower flux of electron donors. Species-level niche separation in most of the dominant taxa was also found between the hadal and abyssal microbial communities. Considering the geomorphology and the isolated hydrotopographical nature of the Mariana Trench, we hypothesized that the distinct hadal microbial ecosystem was driven by the endogenous recycling of organic matter in the hadal waters associated with the trench geomorphology.hadal | trench | niche separation | nitrification | Challenger Deep

Ammonium and nitrite oxidation at nanomolar oxygen concentrations in oxygen minimum zone waters

“…S1): Nitrosopumilus, Nitrosopelagicus water column A, unaffiliated water column B, and marine benthic group B (38)(39)(40). The most abundant thaumarchaeal phylotype observed was affiliated with the Nitrosopumilus cluster, a group that contains cultivated, ammonium-oxidizing representatives (39) and has been observed in a wide array of marine environments (41,42). The Thaumarchaeota observed here displayed close relationships to those observed in permanent and seasonally anoxic OMZs and anoxic basins, such as the eastern tropical South Pacific and Saanich Inlet, respectively (43,44) (Fig.…”

Global diversity and biogeography of deep-sea pelagic prokaryotes

“…In addition, physical transport processes, such as advection, have been proved to act as ecological drivers of marine bacterial communities (Wilkins et al, 2013) but the effect of the deep ocean's floor morphology over the composition of microbial communities was only explored in few locations such as the Walvis Ridge or the Challanger Deep (Schauer et al, 2010;Nunoura et al, 2015). Here we test, at a global scale, the possibility that submarine mountains that divide the deep ocean into deep-oceanic basins may act as 'ecological barriers' for prokaryotic communities: either by (i) imposing a reduced dispersion between basins or (ii) by compartmentalizing the bathypelagic ocean into contrasting environments that exert an ecological selection on the prokaryotes that inhabit it.…”

Perspectives on the Terrestrial Organic Matter Transport and Burial along the Land-Deep Sea Continuum: Caveats in Our Understanding of Biogeochemical Processes and Future Needs

“…Nonetheless and importantly, C (and N) dynamics in this dark world remain completely elusive. Until today, relatively little is heard about the biogeochemistry of hadal trenches (e.g., Glud et al, 2013;Nunoura et al, 2015). These studies believed that patterns of food supply in hadal environments are affected by the physical topography, as the steep slope of trenches facilitate a downward transport and subsequent accumulation of POC along the trench axis, making the supply of nutrients to trench systems fundamentally distinct to that on the flat neighboring abyssal ecosystems.…”

“…Furthermore, compared to abyssal plains, a faster attenuation of oxygen (O 2 ) concentration and high rates of microbial C turnover in sediments have been noted at Challenger Deep due to an intensified O 2 consumption within trench sediments (Glud et al, 2013). Since the hadal microbial ecosystem is distinct and driven by the endogenous recycling of OM (Nunoura et al, 2015), tracking the pulsed sources of OM to these ecosystems would provide new insights into the biogeochemical cycles of C and N and other nutrient-like elements.…”