Much of ocean life lives away from sunlight, the planet’s main source of energy. Are microorganisms that live between 1,000 and 4,000 meters deep and that, in addition to the lack of light, have to adapt to the unique characteristics of high pressure Y low temperature of that ecosystem. Although they play a fundamental role in the biogeochemical cycles of the planet, a large part of these microbial species has not yet been characterized.
63% of these genes cannot be associated with any known function and will surely be important for the functioning of the deep ocean ecosystem
Now, a new study led by researchers from the Institut de Ciències del Mar (ICM-CSIC) has described hundreds of new microbial genomes and has revealed the great metabolic versatility of the deep ocean microbiome through the analysis of metagenomes collected at 4,000 meters during the Malaspina Expedition of the year 2010, whose objective was to study the microorganisms of great depth of the tropical and subtropical latitudes of the main oceans of the Earth.
Until now, it had been assumed that these microorganisms, most bacteria Y arches, were mainly heterotrophic, and depended on organic matter exported from the sunlit layer through sinking particles (fecal zooplankton granules, phytoplankton aggregates, etc.). However, the production of complex organic molecules from CO₂ in the absence of light (chemolithoautotrophy) had also been considered as a possible strategy that supports the high respiratory activity observed in the deepest and darkest ocean.
Instead, published work now suggests that the mixed strategy, that is, the mixotrophy, which refers to the ability to use different sources of energy and carbon to function as an autotroph or heterotroph, is common among bacteria and archaea.
“By analyzing 58 microbial metagenomes from the bathypelagic ocean (mostly 4,000 m deep), we have been able to build the Malaspina Gene DataBase, which includes more than 600,000 genes that are unique to these microbial communities and have not been observed before. ”, Explains the ICM researcher and lead author of the study Silvia G. Acinas, which adds that 63% of these genes cannot be associated with any known function and will surely be important for the functioning of the deep ocean ecosystem.
Unknown bacteria and archaea
“With these metagenomes we have reconstructed 317 deep ocean microbial genomes that include a notable taxonomic novelty, with more than 68% of bacterial genomes and more than 58% of archaea genomes belonging to species not yet described”, he highlights Pablo Sanchez, another of the ICM researchers who participated in the study. In his opinion, “these resources are unique for the scientific community to be able to test other hypotheses about the functioning of the deep ocean.”
These resources are unique so that the scientific community can test other hypotheses about the functioning of the deep ocean.
Pablo Sánchez, ICM researcher
The study, published in the journal Communications Biology, also reveals new genomes of chemolytoautotrophic and myxotrophic prokaryotes, as well as diazotrophic bacteria, that is, microbes capable of fixing nitrogen, but that are not cyanobacteria. Interestingly, some of these nitrogen-fixing genomes also have the genetic potential for autotrophy, and this strategy has not been reported before in the deep ocean.
In this sense, the also ICM researcher and coordinator of the Malaspina microbiology part, Josep M. Gasol, points out that “microbial communities that live freely in the water column (free-living microbes) are metabolically different from those that are mostly associated with particles (microbes attached to particles) in this unexplored ecosystem, regardless of their biogeography ”.
Acinas, SG, et al (2021). “Deep ocean metagenomes provide insight into the metabolic architecture of bathypelagic microbial communities”. Communications Biology, 4 (1), 1-15.
Rights: Creative Commons.