Bacterial Succession on Sinking Particles in the Ocean's Interior

Abstract

Sinking particles formed in the photic zone and moving vertically through the water column are a main mechanism for nutrient transport to the deep ocean, and a key component of the biological carbon pump. The particles appear to be processed by a microbial community substantially different from the surrounding waters. Single cell genomics and metagenomics were employed to describe the succession of dominant bacterial groups during particle processing. Sinking particles were extracted from sediment traps at Station Aloha in the North Pacific Subtropical Gyre (NPSG) during two different trap deployments conducted in July and August 2012. The microbial communities in poisoned vs. live sediment traps differed significantly from one another, consistent with prior observations by Fontanez et al. (2015). Partial genomes from these communities were sequenced from cells belonging to the genus Arcobacter (commensalists potentially associated with protists such as Radiolaria), and Vibrio campbellii (a group previously reported to be associated with crustacea). These bacteria were found in the particle-associated communities at specific depths in both trap deployments, presumably due to their specific host-associations. Partial genomes were also sequenced from cells belonging to Idiomarina and Kangiella that were enriched in live traps over a broad depth range, that represented a motile copiotroph and a putatively non-motile algicidal saprophyte, respectively. Planktonic bacterial cells most likely caught in the wake of the particles belonging to Actinomarina and the SAR11 clade were also sequenced. Our results suggest that similar groups of eukaryote-associated bacteria are consistently found on sinking particles at different times, and that particle remineralization involves specific, reproducible bacterial succession events in oligotrophic ocean waters.

Metabolite composition of sinking particles reflects a changing microbial community and differential metabolite degradation

“…Here we show that the metabolite composition of sinking particles throughout the western South Atlantic gyre, equatorial region, and tropical North Atlantic was relatively constant and showed no relationship to the metabolite composition of suspended particles in the euphotic zone or to differences in the numerical contribution of diatom or coccolithophore cells to the overall particle flux. The observation that the metabolite composition of sinking particles differed from that of suspended particles was consistent with the observation that microbial community composition also differs on sinking particles from the community in seawater (Fontanez et al 2015;Thiele et al 2015;Pelve et al 2017). This may be related to differences in community composition and metabolic strategies associated with sinking particles such as the possible utilization of proline and glycine betaine as osmolytes on sinking particles.…”

“…Similar bacterial communities on sinking particles could lead to similar metabolite compositions, particularly if the metabolic pathways associated with organic matter degradation produce a characteristic profile of metabolic intermediates. This composition could be dynamic reflecting a succession process as the particles are transformed on their downward transport through the water column (Pelve et al 2017). We expect that the metabolite composition of the sinking particles along the transect is shaped by the removal of metabolites through microbial respiration, the production of molecules from the breakdown of larger molecules derived from the sinking particle organic matter pool, and production of molecules associated with the physiological requirements of the sinking particle-associated microbial community.…”

Copepods promote bacterial community changes in surrounding seawater through farming and nutrient enrichment

“…The zoosphere-associated bacteria are among the most commonly reported bacteria in copepods (Shoemaker and Moisander, 2015;Datta et al, 2018). These groups are also regularly reported from oceanic particle-associating bacterial communities (López-Pérez et al, 2016;Pelve et al, 2017). Yet, it is challenging to make quantitative estimates about the importance of substrate-associated bacteria given the transient nature of the associations.…”

Summer comes to the Southern Ocean: how phytoplankton shape bacterioplankton communities far into the deep dark sea

“…The second question was about the fate of the bloom and its potential impact on the mesopelagic bacterial community structure. The sedimenting flux of detritus is known to be an important factor structuring bacterioplanktonic communities below the euphotic zone (Pelve et al 2017), and most of the ocean's surface-generated organic matter undergoes recycling in the mesopelagic ocean (Buesseler et al 2007, Buesseler and Boyd 2009, Giering et al 2014. Carbon budgets suggest, and measurements confirm, that significant mesopelagic bacterial activity occurs in the ASP (Ducklow et al 2015, Williams et al 2016) below the bloom.…”

“…The sedimenting flux of detritus is known to be an important factor structuring bacterioplanktonic communities below the euphotic zone (Pelve et al. ), and most of the ocean's surface‐generated organic matter undergoes recycling in the mesopelagic ocean (Buesseler et al. , Buesseler and Boyd , Giering et al.…”