The percentage of living bacterial cells related to organic carbon release from senescent oceanic phytoplankton

Abstract

Abstract. Bacteria recycle vast amounts of organic carbon, playing key biogeochemical and ecological roles in the ocean. Bacterioplankton dynamics are expected to be dependent on phytoplankton primary production, but there is a high diversity of processes (e.g., sloppy feeding, cell exudation, viral lysis) involved in the transfer of primary production to dissolved organic carbon available to bacteria. Here, we show the percentage of living heterotrophic bacterioplankton in the subtropical NE Atlantic Ocean in relation to phytoplankton extracellular carbon release (PER). PER represents the fraction of primary production released as dissolved organic carbon. PER variability was explained by phytoplankton cell death, with communities experiencing higher phytoplankton cell mortality showing a larger proportion of phytoplankton extracellular carbon release. Both PER and the percentage of dead phytoplankton cells increased from eutrophic to oligotrophic waters, while abundance of heterotrophic bacteria was highest in the intermediate waters. The percentage of living heterotrophic bacterial cells (range: 60-95 %) increased with increasing phytoplankton extracellular carbon release from productive to oligotrophic waters in the subtropical NE Atlantic. The lower PERs, observed at the upwelling waters, have resulted in a decrease in the flux of phytoplankton dissolved organic carbon (DOC) per bacterial cell. The results highlight phytoplankton cell death as a process influencing the flow of dissolved photosynthetic carbon in this region of the subtropical NE Atlantic Ocean, and suggest a close coupling between the fraction of primary production released and heterotrophic bacterial cell survival.

Eddy enhanced primary production accelerates bacterial growth in the Eastern Tropical North Atlantic

“…We did not observe a marked gradient in phytoplankton productivity either, unlike other regions of the CanUS with permanent upwelling conditions (Demarcq and Somoue, 2015;Arístegui et al, 2020). PPTOT rates stayed rather constant from the coast to the open ocean and were in the range of reported rates in oligotrophic offshore waters of the CanUS (Agustí and Duarte, 2013;Lasternas et al, 2014). SL-DOC was relatively constant as well, with variations attributable to the westward propagation of the currents and eddies (SI Fig.…”

“…Indeed, plankton mortality rates have been reported to increase with decreasing cell size (Marbá et al, 2007) and with increasing PER (Lasternas et al, 2014). Agustí and Duarte (2013) reported PER to range from ~1% in 'healthy' communities from the upwelled waters of the CanUS to ~70% in 'dying' communities from the oligotrophic waters of the ETNA.…”

Eddy-enhanced primary production sustains heterotrophic microbial activities in the Eastern Tropical North Atlantic

“…When excluding the eddy-influenced stations, there was no marked gradient in phytoplankton productivity either, unlike other regions of the CanUS (Demarcq and Somoue, 2015;Arístegui et al, 2020). PP TOT and PP DOC rates stayed rather constant from the coast to the open ocean and were in the range of reported rates in oligotrophic offshore waters of the CanUS (Agustí and Duarte, 2013;Lasternas and Agustí, 2014). The spatial distribution of SL-DOC was relatively uniform as well when considering the coastal and open ocean stations only.…”

“…For example, Agustí and Duarte (2013) reported PER to range from ∼ 1 % in "healthy" communities from the upwelled waters of the CanUS to ∼ 70 % in "dying" communities from the oligotrophic waters of the ETNA. PER values have been reported to increase with nutrient depletion (Obernosterer and Herndl, 1995;Agustí and Duarte, 2013;Lasternas et al, 2014;Piontek et al, 2019) among other factors (see review by Mühlenbruch et al, 2018). Since upwelling was weak during our sampling period, low nutrient concentrations in the surface waters might explain the relatively high PER that we observed near the coast.…”

Low Host Abundance and High Temperature Determine Switching from Lytic to Lysogenic Cycles in Planktonic Microbial Communities in a Tropical Sea (Red Sea)

“…The concentrated heterotrophic bacterial cells were rinsed five to six times with 100 mL of VFW and then resuspended until a volume of 250-300 mL was reached [50][51][52]. The Amicon ® stirred ultrafiltration cell is an advantageous concentration system as it gives high flow rates and is capable of concentrating samples rapidly but gently, as was successfully used previously in quantifying living cells [53,54]. The system uses magnetic stirring and pressure-driving filtration, resulting in a short time required for cell concentration (i.e., less than half an hour in our samples).…”