Hadal zone microbial communities
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Hadal zone microbial communities are the groups of microorganisms which reside within hadal zones, which consist of many individual deep oceanic trenches found around the world.[1]
The environmental conditions of the trench environments select for the microbe communities. Generally, the environmental properties of the hadal zone are similar to the abyssal; temperature varies between different trenches, as do salinity and nutrients.[2] A unique characteristic of these hadal zones is the large abundance and accumulation of particulate organic matter in these trenches. These high concentrations correspond directly to high microbial productivity.[3] The physical bathymetry of the trenches is also critical to understandings of microbial communities as this influences the distribution of organic matter.[4] Microbes play a great role in the cycling of this organic matter and other nutrients within the hadal zone.[5]
Hadal zone microbial communities are highly diverse, and include bacteria, archaea as well as viruses. Hadal zone bacterial sediment communities are much more abundant than adjacent abyssal communities thus implicating the importance of distinguishing these two microbial communities.[6] Archaeal microbes also make up a substantial portion of hadal microbial communities and are in fact found to be the most abundant within hadal sediments.[6] Although viral communities have been found to be in a greater amount than nearby abyssal zones, a large proportion of viral genomes are unknown and thus suggest a large gap in viral knowledge within hadal zones.[7]
As the microbial community composition in the hadal zones is incredibly diverse, so is their metabolic potential. The accumulation of organic matter results in the hadal zone being a metabolically rich environment.[8] The most dominant form of metabolism utilized by hadal zone microbes is heterotrophic microbial metabolism.[9] Other forms of dominant metabolism include fermentation,[10] anammox,[11] denitrification,[12] sulfate reductive metabolism,[12] as well as chemolithotrophic pathways such as sulfur oxidation, iron oxidation, nitrification and carbon fixation.[10] Surprisingly, despite the low oxygen conditions, aerobic metabolic potential has also been identified.[10] No phototrophic lifestyles have been found within hadal zone microbes.[9]
With 37 hadal trenches around the globe, the importance of understanding hadal microbial communities and community composition can not be overstated.[13] However, a deep understanding of the microbial ecosystem in the hadal zone still remains largely uncharacterized. It remains one of the least studied and explored microbial habitats due to difficulties with sampling.[14] Exploring the hadal zone and its communities can shed light on the dark biosphere[15] as well as possible aid scientists in exploring oceans even beyond Earth.[16]