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Bacteria and archaea regulate particulate organic matter export in suspended and sinking marine particle fractions
Dithugoe, Choaro D.; Bezuidt, Keoagile Ignatius Oliver; Cavan, Emma L.; Froneman, William P.; Thomalla, Sandy J.; Makhalanyane, Thulani P.
The biological carbon pump (BCP) in the Southern Ocean is driven by
phytoplankton productivity and is a significant organic matter sink. However, the role
of particle-attached (PA) and free-living (FL) prokaryotes (bacteria and archaea) and their
diversity in influencing the efficiency of the BCP is still unclear. To investigate this, we
analyzed the metagenomes linked to suspended and sinking marine particles from the
Sub-Antarctic Southern Ocean Time Series (SOTS) by deploying a Marine Snow Catcher
(MSC), obtaining suspended and sinking particulate material, determining organic carbon
and nitrogen flux, and constructing metagenome-assembled genomes (MAGs). The
suspended and sinking particle-pools were dominated by bacteria with the potential to
degrade organic carbon. Bacterial communities associated with the sinking fraction had
more genes related to the degradation of complex organic carbon than those in the
suspended fraction. Archaea had the potential to drive nitrogen metabolism via nitrite
and ammonia oxidation, altering organic nitrogen concentration. The data revealed several
pathways for chemoautotrophy and the secretion of recalcitrant dissolved organic
carbon (RDOC) from CO2, with bacteria and archaea potentially sequestering particulate
organic matter (POM) via the production of RDOC. These findings provide insights into
the diversity and function of prokaryotes in suspended and sinking particles and their
role in organic carbon/nitrogen export in the Southern Ocean.
IMPORTANCE : The biological carbon pump is crucial for the export of particulate organic
matter in the ocean. Recent studies on marine microbes have shown the profound influence
of bacteria and archaea as regulators of particulate organic matter export. Yet, despite
the importance of the Southern Ocean as a carbon sink, we lack comparable
insights regarding microbial contributions. This study provides the first insights regarding
prokaryotic contributions to particulate organic matter export in the Southern Ocean.
We reveal evidence that prokaryotic communities in suspended and sinking particle fractions
harbor widespread genomic potential for mediating particulate organic matter
export. The results substantially enhance our understanding of the role played by microorganisms
in regulating particulate organic matter export in suspended and sinking marine
fractions in the Southern Ocean.