Sedimentation of ballasted cells‐free EPS in meromictic Fayetteville Green Lake

Abstract

Fayetteville Green Lake (FGL) is a recognized, extensively studied present‐day model of the stratified Proterozoic ocean. Nonetheless, biomass sedimentation in FGL remains hard to explain: while virtually all sediment pigments belong to photosynthetic sulfur bacteria from a chemocline, the isotopic carbon signature of the bulk organic matter suggests its epilimnetic phytoplankton origin. To explain the epilimnetic origin of sedimented carbon, we studied the dominant Synechococci, isolated from FGL. Here, we present experimental evidence that FGL Synechococci produce copious extracellular polysaccharides (EPS) especially when availability of inorganic carbon (Ci) is high relative to availability of other macronutrients, for example phosphorus. The accumulating EPS become impregnated with calcium, magnesium, and sodium cations and are released to the environment as ballasted cell coverings. Sedimentation of these cell‐free EPS can constitute the bulk of pigment‐free organic material in FGL sediment. Because increased availability of Ci specifically stimulates production of EPS and the accumulated EPS adsorb cations and become ballasted, we propose the universal role of cyanobacterial EPS in biomass sedimentation in the high‐Ci Paleoproterozoic ocean as well as in modern aquatic systems like FGL.

Deep photoautotrophic prokaryotes contribute substantially to carbon dynamics in oxygen‐deficient waters in a permanently redox‐stratified freshwater lake

“…7). These data could be explained by the presence of particulate‐iron‐rich gel particles above the pycnocline (Kamennaya et al 2020). If Ferribacterium resides in gel particles, which are easily disturbed during filtration (Engel 2009), they could pass through the 2.7‐ μ m filter.…”

A re‐examination of the mechanism of whiting events: A new role for diatoms in Fayetteville Green Lake (New York, USA)

“…2d, 6), and possibly "bag-like" empty EPS envelopes detached from Synechococcus cells (Fig. 4d,f) (Kamennaya et al, 2020). A significant portion of the diatom EPS likely consists of β-chitin fibrils, found associated with calcite particles later in the summer (Figs.…”

“…4). The spherical cells are relatively small (~0.8 µm in diameter), and likely correspond to cyanobacteria of the genus Synechococcus, the dominant autotrophs in Green Lake Schultze-Lam et al, 1997;Kamennaya et al, 2020). Diatoms and bacteria are found amidst extracellular organic material, forming either fibrils or thin films, and interpreted as EPS produced by microbial cells and/or diatoms.…”

“…No XANES spectra were acquired on these objects, preventing calculations of IC/ICa ratios. These round shaped calcium enrichments may correspond to "bag-like" EPS envelopes issued from Synechococcus cells, which can dissociate from the cells and have high Ca 2+ adsorption capacity (Kamennaya et al, 2020).…”

Particle-associated and free-living microbial assemblages are distinct in a permanently redox-stratified freshwater lake

“…However, Ferribacterium and Rhodoferax sequences were equally likely to be recovered in both assemblage types (over-representation factor ∼ 0). This unexpected assemblage partitioning of iron-reducers could be explained by the documented existence of particulate-iron-rich extracellular polymeric substances (EPS) at non-sulfidic depths in FGL (Kamennaya et al, 2020), as iron cycling is promoted in EPS (Chiu et al, 2017). If iron-reducers do reside in EPS in FGL, which is easily disturbed during filtration (Engel, 2009), they could pass through the 2.7 µ m filter.…”