The effects of cyanobacteria and dissolved organic carbon on marine trace metal cycling

• Author / Creator

  Bishop, Brendan A

• Trace metals have been estimated to be required in one-quarter to one-third of all proteins as cofactors in metalloenzymes which code for numerous crucial biological processes such as respiration, photosynthesis, DNA and RNA synthesis, nitrogen fixation, and electron transfer reactions. However, the marine bioavailability of these trace metals is affected by complexation with microbes and organic ligands. Microbial biomass is an important vector involved in the adsorption and cycling of marine biomass due to its negative surface charge at marine conditions and high surface area to volume ratio. Furthermore, the majority of trace metals in seawater are complexed with dissolved organic ligands. Most of these ligands are produced autochthonously by cyanobacteria who use these ligands to alter the bioavailability of nutrients. Therefore, studying the interplay between microbes, dissolved organic molecules, and trace metals is critical in understanding marine nutrient cycles. Gaining insights into the interplay between biomass and trace metals is also critical for understanding the evolution of metalloenzymes and long-term trace element bioavailability, since it has been hypothesized that metalloenzymes reflect marine nutrient availability at their time of evolution. Furthermore, biomass can also be a sink for trace metals, acting as a sink for trace metals into sediments with these signatures being preserved in the rock record.
  This study explores the surface reactivity and adsorption of the bioessential trace elements Co, Ni, Cu, and Zn to the cell wall of the marine cyanobacterium Synechococcus sp PCC 7002 and Synechococcus-derived dissolved organic carbon using a surface complexation modelling approach. Synechococcus and its lysate, an analogue for DOC, have similar surface properties as determined by FTIR analysis and titration data in conjunction with SCM. Titration data for both was modelled using a 3-site protonation model, while FTIR analysis determined the presence of carboxyl, phosphoryl, hydroxyl, and amine groups. Although the general properties of Synechococcus and its lysate were similar, the lysate exhibited lower pK¬a values as well as significantly higher site concentrations for each of the sites. Metal binding experiments were performed by means of pH edges to determine the adsorption capacity of Synechococcus, followed by surface complexation modelling of the adsorption data to calculate thermodynamic binding constants for each of the metals. These thermodynamic binding constants were then used to predict the adsorption of the metals in a competitive system, where the adsorption pattern of Zn>Cu>Ni>Co was accurately forecasted. This study aims to increase our understanding of the importance of trace metal adsorption to marine organic ligands and their influence on trace metal cycling.

• Subjects / Keywords

  • trace metal cycling
  • surface complexation modelling
  • banded iron formation
  • cyanobacteria
  • dissolved organic carbon

• Graduation date

  Fall 2018

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3639KM84

• License

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