Activation of Methanogenesis by Cadmium in the Marine Archaeon Methanosarcina acetivorans

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.

Cd2+ resistance mechanisms in Methanosarcina acetivorans involve the increase in the coenzyme M content and induction of biofilm synthesis

“…In HDCS incubated with acetate, methane production was increased by 1–250 μM Cd 2+ (Fig. ), as reported previously (Lira‐Silva et al ., ), whereas in HDCS incubated with methanol, methane production was not affected by Cd 2+ (Fig. ).…”

“…Values shown for the sum of total thiol molecules (total) was given for the total content of cellular protein per culture. In acetate, the total cellular protein was 5.1–6.4 mg/culture, and in methanol was 8.9–10.2 mg/culture (Lira‐Silva et al ., ). b.…”

“…In a previous work, we demonstrated that M. acetivorans growth was not inhibited by 100 μM CdCl 2 , and that the intracellular metal accumulation activated some enzymes of methanogenesis (Lira‐Silva et al ., ), suggesting that these Archaea cells have efficient resistance mechanisms against heavy metals. However, it was not determined why cells can resist such high Cd 2+ stress.…”

“…For instance, in acetate-grown cells at low (10 μM total Cd 2+ or 72 pM free Cd 2+ ) and high concentrations (500 μM or 63 μM free Cd 2+ ), 33% and 26% of Cd 2+ is removed, which is accompanied by increases of 3 and 20 times in S 2− Values shown for the sum of total thiol molecules (total) was given for the total content of cellular protein per culture. In acetate, the total cellular protein was 5.1-6.4 mg/culture, and in methanol was 8.9-10.2 mg/culture (Lira-Silva et al, 2012). b.…”

“…We recently reported that in cultures of the marine methanogen Methanosarcina acetivorans, external reduced Cys and sulfide ameliorate the Cd 2+ toxic effects, which rather stimulated methanogenesis in short-term experiments (Lira-Silva et al, 2012). The cells were also able to remove and accumulate a significant fraction of the cadmium present in the medium.…”