Abstract
Deep-sea ecosystems represent the largest and most remote biome of the biosphere. They play a fundamental role in global biogeochemical cycles and their functions allow existence of life on our planet. In the last 20 years enormous progress has been made in the investigation of deep-sea microbes, but the knowledge of the microbial ecology of the soft bottoms (representing >90% of the deep-sea floor surface) is still very limited. Deep-sea sediments host the largest fractions of Bacteria, Archaea and viruses on Earth, and potentially, a high diversity. At the same time, available results from metagenomics suggest that a large fraction of microbial taxa is completely unknown to science. Estimating the diversity of deep-sea benthic microbes and understanding their functions are some of the challenges of absolute priority, not only for deep-sea microbial ecology, but also for the entire research field of life sciences. The achievement of these goals, given the importance of the deep-sea microbial life for the functioning of the global biosphere, will open new perspectives for the comprehension of adaptation processes to the impact of global changes.
Highlights
Reviewed by: Takuro Nunoura, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Japan Brett J
Current estimates indicate that only 5% of the deep oceans has been explored in detail so far, and that less than 0.001% has been sampled and described in detail in terms of biodiversity (Snelgrove, 1999; Danovaro, 2010; Danovaro et al, 2014)
Most of the interest from scientists has been focused on habitats of deep-sea environments such as hydrothermal vents, cold seeps, and subsurface sediments where life conditions are even more extreme. Since such habitats contribute for a likely negligible fraction to entire deep-sea floor, this overview will focus on the knowledge on the ecology of benthic bacteria, archaea, and viruses of deep-sea “soft bottoms.”
Summary
Researchers have documented life everywhere in the deep sea, including the deepest trenches with active metabolic life from −2 to >150◦C, and microbial life even in sediments at 10,000 m depth and at 1000 m below the seafloor (Jørgensen and Boetius, 2007) In these benthic ecosystems, biomass is generally dominated by microbes belonging to the domains of Bacteria and Archaea, and by unicellular eukaryotes, which are fundamentally important for C cycling and nutrient regeneration and are vital for sustaining oceanic production (Middelburg and Meysman, 2007; Danovaro et al, 2014). The shunt of most of the heterotrophic carbon production into organic detritus due to viral lysis is a crucial process for sustaining the high prokaryotic biomass of deep-sea ecosystems and provides an important contribution to prokaryotic metabolism, allowing the deep-sea ecosystems to cope with the severe organic resource limitation (Danovaro et al, 2008b).
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