Nickel is an essential element for marine microorganism, which is identified as a component in several enzymes, participating in metabolic reactions such as hydrogen metabolism, ureolysis and methane biogenesis. The cycling and bioavailability of Ni on the Earth’s surfaces controls the metabolism of aqueous microorganisms. Synechosystis PCC. 6803 is a genus of unicellular, planktonic cyanobacteria that performs oxygenic photosynthesis primarily in freshwater. Due to the high surface area and surface charge of Synechosystis PCC. 6803, it shows adsorption capacity to trace elements under aqueous environment. Understanding the affinity of Ni on the surface of Synechosystis PCC. 6803 is critical to comprehend the source, sink and transport in the natural environment.
In this work, we conducted Ni adsorption experiments on synnechocystis sp.PCC 6803 surfaces as a function of pH edge (pH range 3-9) under freshwater (0.01M NaCl) ionic strength. Results show that Ni adsorption increases with the increase of pH, with the highest Ni adsorption reaching 74.7% at pH=9. Briefly, the Ni adsorption is minimal (9.46% to 11.55%) between pH=3 and 6, but increases dramatically at pH above 7. A surface complexation model (SCM) was established using FITEQL 4.0 to simulate the adsorption behavior of Ni on the surface of synnechocystis sp.PCC 6803. Based on previous studies, both 2-site and 3-site protonation models were tested. Our modeling results show that the Ni adsorption behavior was better modeled using a non-electrostatic 3-site protonation model. By contrast, the 2-site protonation model underestimated the Ni adsorption behavior from pH3 to 6.
Our results demonstrate the potential in Ni removal and sorption. And the change of adsorption capacity with pH indicates a possible link in Ni cycle in the estuary area.
 

Synechocystis,Nickel adsorption,Metal cycling