Fig. 1

Methane consumption by ANME-1 Mcr-producing M. acetivorans during high-density growth experiments. All values are presented as mean ± sem of three cultures. **P ≤ 0.05, *P < 0.15. a Methane consumption of cells harboring pES1-MATmcr1 (Mcr1), pES1-MATmcr2 (Mcr2), pES1-MATmcr3 (Mcr3), and pES1(Pmat) (Empty) after 5 days showing that pES1-MATmcr3 is the best construct in performing reverse methanogenesis in M. acetivorans. The absence of cells (No cells) in the same growth medium (HS-methane medium and 0.1 mM FeCl₃ and puromycin) showing negligible methane reduction confirmed minimal gas leakage from the tubes. b Increase in methane consumption by high cell-density cultures of M. acetivorans/pES1-MATmcr3 (Mcr3) in comparison to pES1(Pmat)-harboring cells (Empty) for 5 days showing the importance of the cloned mcr. c Higher production of extracellular acetate was observed for high cell-density cultures of M. acetivorans/pES1-MATmcr3 (Mcr3) than for M. acetivorans/pES1(Pmat) (Empty), M. acetivorans/pES1-MATmcr2 (Mcr2), and M. acetivorans/pES1-MATmcr1 (Mcr1) after 5 days on methane and 0.1 mM FeCl₃. The absence of cells (No cells) in the same growth medium (HS-methane medium with 0.1 mM FeCl₃ and puromycin) showing negligible extracellular acetate confirmed minimal abiotic formation of acetate