Synechococcus silicon accumulation in oligotrophic oceans

Abstract

Si accumulation by Synechococcus, small unicellular marine picocyanobacteria that dominate in nutrientdepleted waters, is significant due to its potential to alter our understanding of the global Si cycle. To date, however, there are only a few studies on Si accumulation in individual Synechococcus cells. To determine the magnitude and variability of Synechococcus cellular Si content in oligotrophic oceans, we analyzed 1348 discrete cells collected from the understudied eastern Indian Ocean (EIO) and western Pacific Ocean (WPO). Synechococcus cellular Si quotas varied widely across both regions, ranging from 0 to 4651 amol Si cell À1 . While highly variable in range, average Si quotas were $ 2.5-fold lower in Synechococcus cells from the EIO (172 AE 304 amol Si cell À1 ) than in those from the WPO (438 AE 737 amol Si cell À1 ). The estimated contributions of Synechococcus to total and picoplankton biogenic Si stocks were < 1-8% and 1-11%, respectively, suggesting that Synechococcus has a small but persistent regional contribution to biogenic Si stocks. Here, we also made a first-order estimate of the Synechococcus biogenic Si stock for the global ocean, that is, 0.06-0.09 Tmol Si, accounting for 2-3% of the global ocean diatom Si stock. No significant effects of temperature and dissolved inorganic N and P on cellular Si quotas were observed within these oligotrophic ecosystems. However, salinity, ambient dissolved Si, and N/P ratio were closely correlated with the variable Si quotas with different relationships. In addition, Synechococcus cellular Si/P and Si/S ratios associated with physiological processes were significantly influenced by environmental and geographic variables. We thus suggest that the variance in cellular Si quotas may be indirectly driven by ambient variables via some unknown independent or strain-dependent physiological processes.

Silicification of Cyanobacteria

“…The key elemental behaviors, such as Si buildup or loss in Synechococcus cells, may be indirectly influenced by external variables through independent or strain-dependent physiological processes. This is because of the dynamic balance between cellular elements Si and C, P, and S (Wei et al, 2022) .…”

“…Tang et al (2014) have provided more evidence that Synechococcus -derived bSi standing stock accounts for 50% of the bSi inventory in the surface water, thus implying that half of the bSi in the surface water originates from Synechococcus . A recent study estimated that cyanobacteria responsible for 0.06–0.09 Tmol Si in the global ocean account for 2–3% of the diatom Si stock (Wei et al, 2022) .…”

“…Cyanobacteria are like diatoms in terms of DSi fixation (Wei et al, 2022; Wei and Sun, 2022) . A few measurements revealed that there are certain similarities between Synechococcus and the metabolism of Si in diatoms.…”

A Large Silicon Pool in Small Picophytoplankton

“…Conceivably, Si accumulation by picophytoplankton may affect their growth and metabolism, and then regulate their photosynthetic C fixation and biological C pump. More importantly, these small cells may promote the sinking of particulate matter, and all organic C contained therein through their dense siliceous cells or extracellular EPS-Si into the ocean without entering the recycling process ( Tang et al, 2014 ; Wei et al, 2022 ). This potential sinking process is likely to combine the Si cycle with the C cycle, making it a new bridge connecting the interactions of the oceanic C and Si cycles.…”

The silicon transporters (SITs) gene was found inSynechococcussp. XM24

“…However, further investigations into marine ecosystems have revealed challenges in solely attributing silicon and carbon production imbalances in oligotrophic oceans to diatoms. Recent studies have highlighted the dominance of picophytoplankton such as Synechococcus in primary productivity within oligotrophic regions, significantly influencing the export of carbon particles to the deep ocean (Richardson and Jackson, 2007; Lomas and Moran, 2011; Wei et al, 2022). This discovery poses a significant challenge to the established role of diatoms in the global marine silicon cycle (Jun and Yuqiu, 2018).…”