Abstract
Methanosarcina acetivorans was cultured in the presence of CdCl2 to determine the metal effect on cell growth and biogas production. With methanol as substrate, cell growth and methane synthesis were not altered by cadmium, whereas with acetate, cadmium slightly increased both, growth and methane rate synthesis. In cultures metabolically active, incubations for short-term (minutes) with 10 µM total cadmium increased the methanogenesis rate by 6 and 9 folds in methanol- and acetate-grown cells, respectively. Cobalt and zinc but not copper or iron also activated the methane production rate. Methanogenic carbonic anhydrase and acetate kinase were directly activated by cadmium. Indeed, cells cultured in 100 µM total cadmium removed 41–69% of the heavy metal from the culture and accumulated 231–539 nmol Cd/mg cell protein. This is the first report showing that (i) Cd2+ has an activating effect on methanogenesis, a biotechnological relevant process in the bio-fuels field; and (ii) a methanogenic archaea is able to remove a heavy metal from aquatic environments.
Highlights
Methanogenesis is the pathway by which ion (H+, Na+) gradients across the plasma membrane are generated to drive ATP synthesis, with the concomitant production of methane as an end product
Methanogens are strict anaerobes belonging to the Archaea domain, which can be found in a broad variety of environments such as anaerobic digesters of sewage treatment plants, landfills, rice paddies, lakes and in the sea sediments, among others [1]
Chemicals Acetate kinase from M. thermophila, deoxyribonuclease I from bovine pancreas (DNAse I), acetyl-CoA, coenzyme A, acetyl phosphate, ATP and NADH were purchased from Sigma Chem
Summary
Methanogenesis is the pathway by which ion (H+, Na+) gradients across the plasma membrane are generated to drive ATP synthesis, with the concomitant production of methane as an end product. Methanogens are strict anaerobes belonging to the Archaea domain, which can be found in a broad variety of environments such as anaerobic digesters of sewage treatment plants, landfills, rice paddies, lakes and in the sea sediments, among others [1]. These organisms have an essential role in the global carbon cycle by transforming small carbon molecules such as methanol, methylamines, CO2+H2, formate, CO and acetate into methane. Depending on the physicochemical environmental characteristics and microbial metabolism, heavy metal contaminants may be released from sediments back into the water Under such situations, marine sediments may become a secondary source of pollution
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