Table 2 Overview of bacterial metabolic processes that facilitate carbonate precipitation.
From: Understanding biofouling and contaminant accretion on submerged marine structures
Metabolic process | Known bacterial groups/candidates | Metabolic enzymes | How the metabolic process induces precipitation |
|---|---|---|---|
Ureolytic bacteria | Urease, Carbonic anhydrase | The process behind urea hydrolysis releases ammonium, bicarbonate, and hydroxyl ions. This synergistically acts with carbonic anhydrase which catalyzes the reversible reaction of water and carbon dioxide into carbonic acid. Both processes result in a net increase in pH and increasing levels of bicarbonate, driving carbonate precipitation. | |
Methanogens | Methane monooxygenase | In anaerobic conditions, methane oxidation results in bicarbonate which in the presence of calcium ions precipitates into calcium carbonate. | |
Nitrate-reducing bacteria | Nitrate reductase | Denitrification induces carbonate precipitation through the production of carbon dioxide and hydroxyl ions, as well as the consumption of hydrogen ions in the metabolic process. The increase in pH and levels of carbon dioxide in the presence of calcium ions drive the precipitation of calcium carbonate. | |
Sulfate-reducing bacteria | Dissimilatory sulfite reductase | The processes that reduce sulfate into sulfide also oxidizes organic carbon into carbonate, as well as consuming hydrogen ions increasing the favorability of carbonate precipitation. In addition, sulfate-reducing bacteria are known to degrade carboxylic acids with calcium complexation, releasing calcium ions into the surrounding environment, further driving the precipitation of calcium carbonates. | |
Cyanobacteria | RuBisCO; Carbonic anhydrase | In photosynthetic microorganisms, carbonates ions diffuse into the cell and is converted by carbonic to carbon dioxide and hydroxyl ions, whereby the carbon dioxide is converted into organic compounds by RuBisCO and the hydroxyl ions diffuse out of the cell. To maintain pH levels in the cell, antiporters exchange intracellular calcium ions for extracellular hydrogen ions. These combined processes result in an increase in pH and calcium ions in the surrounding environment, promoting the precipitation of calcium carbonate. | |
Alcanivorax borkumensis, Myxococcus xanthus | Urease, Nitrite reductase, Putative enzymes comprised of deaminases, hydratases, peptidases, and proteases | This process includes urea hydrolysis, as well as parts of the denitrification pathways in nitrogen metabolism. In an alternative denitrification pathway, nitrite undergoes dissimilatory nitrate reduction to ammonium via nitrite reductase. Alternatively, proteins and amino acids are broken down by a variety of enzymes, whereby ammonium and sometimes carbon dioxide is released as a byproduct. Like urea hydrolysis and denitrification, a resultant net increase in pH and bicarbonate production drives favorability toward precipitation of carbonate compounds. | |
Bacillus subtilis | Putative flavoproteins | B. subtilis is an ureolytic bacteria that has been observed to precipitate calcite (a polymorph of calcium carbonate) in the absence of urea. A likely enzymatic candidate was a putative heterodimeric flavoprotein associated with fatty acid metabolism. A study showed calcite precipitation in the wild type, but not in knockout strains when the associated flavoprotein gene was modified. |
