Effect of Culture pH on Properties of Exopolymeric Substances from Synechococcus PCC7942: Implications for Carbonate Precipitation

Abstract

The role of culture conditions on the production of exopolymeric substances (EPS) by Synechococcus strain PCC7942 was investigated. Carbonate mineral precipitation in these EPS was assessed in forced precipitation experiments. Cultures were grown in HEPES-buffered medium and non-buffered medium. The pH of buffered medium remained constant at 7.5, but in non-buffered medium it increased to 9.5 within a day and leveled off at 10.5. The cell yield at harvest was twice as high in non-buffered medium than in buffered medium. High molecular weight (>10 kDa) and low molecular weight (3–10 kDa) fractions of EPS were obtained from both cultures. The cell-specific EPS production in buffered medium was twice as high as in non-buffered medium. EPS from non-buffered cultures contained more negatively charged macromolecules and more proteins than EPS from buffered cultures. The higher protein content at elevated pH may be due to the induction of carbon-concentrating mechanisms, necessary to perform photosynthetic carbon fixation in these conditions. Forced precipitation showed smaller calcite carbonate crystals in EPS from non-buffered medium and larger minerals in polymers from buffered medium. Vaterite formed only at low EPS concentrations. Experimental results are used to conceptually model the impact of pH on the potential of cyanobacterial blooms to produce minerals. We hypothesize that in freshwater systems, small crystal production may benefit the picoplankton by minimizing the mineral ballast, and thus prolonging the residence time in the photic zone, which might result in slow sinking rates.

Biocement from the ocean: Hybrid microbial-electrochemical mineralization of CO2

“…We reasonably assumed that CaCO 3 precipitation rate is related proportionally to cyanobacteria organic carbon on a molar basis such that: where is the MICP rate with the unit of g s −1 . This value is in between a theoretical molar ratio of 1 based on the metabolic pathway for cyanobacterial MICP and experimental data for other calcifying cyanobacteria ( Bundeleva et al., 2016 ; Martinho de Brito et al., 2022 ).…”

Biodegradation of Choline NTF2 by Pantoea agglomerans in Different Osmolarity. Characterization and Environmental Implications of the Produced Exopolysaccharide

“…This low molecular weight that this EPS presented was due to the osmotic conditions. Extreme environmental conditions can give rise to low molecular weight EPSs, as was the case of the EPS produced by Synechococcus PCC7942, with a molecular weight of 3-10 KDa [68].…”

“…presented was due to the osmotic conditions. Extreme environmental conditions can give rise to low molecular weight EPSs, as was the case of the EPS produced by Synechococcus PCC7942, with a molecular weight of 3-10 KDa [68]. The EPS produced by P. agglomerans uam8 from biodegrading 0.6 M Choline NTF2 was analyzed by gas chromatography GC-MS Figure 3c.…”