Experimental evidence of an acetate transporter protein and characterization of acetate activation in aceticlastic methanogenesis ofMethanosarcina mazei

Abstract

Aceticlastic methanogens metabolize acetate to methane and carbon dioxide. The central metabolism and the electron transport chains of these organisms have already been investigated. However, no particular attention has been paid to the mechanism by which acetate enters the archaeal cell. In our study we investigated Methanosarcina mazei acetate kinase (Ack) and the acetate uptake reaction. At a concentration of 2 mM acetate, the Ack activity in cell extract of M. mazei was not limiting for the methane formation rate. Instead, the methanogenesis rate was controlled by the substrate concentration and increased 10-fold at 10 mM acetate. Subsequently, we analyzed the involvement of the putative acetate permease MM_0903 using a corresponding deletion mutant. At 2 mM acetate, only 25% of the wild-type methane formation rate was measured in the mutant. This indicated that the supply of acetate to Ack was limiting the rate of methane formation. Moreover, the mutant revealed an increased acetate kinase activity compared with the wild type. These results show for the first time that an acetate transporter is involved in aceticlastic methanogenesis and may be an important factor in the acetate threshold concentration for methanogenesis of Methanosarcina spp.

Limited Mechanistic Link Between the Monod Equation and Methanogen Growth: a Perspective from Metabolic Modeling

“…Instead, methanol consumption by MTA in the cytosol determines the uptake flux of methanol, and hence the growth rate. Finally, these results are consistent with laboratory reports that microbial growth on other nutrients, such as glucose and acetate, is controlled by different enzymes at high and low substrate concentrations ( 54 , 57 ).…”

Methanosarcina acetivorans: A Model for Mechanistic Understanding of Aceticlastic and Reverse Methanogenesis

“…AceP from Ms. acetivorans was shown to transport acetate by a proton symport mechanism ( Ribas et al, 2018 ). A homolog of AceP was shown to be required for acetate transport of acetate in Ms. mazei , and an AceP homolog is encoded in the genome of Methanothrix thermophila ( Smith and Ingram-Smith, 2007 ; Welte et al, 2014 ). The transported acetate is converted to acetyl-CoA by acetate kinase (Ack) and phosphotransacetylase (Pta) in Methanosarcina , and by the AMP-forming acetyl-CoA synthetase (Acs) in Methanothrix ( Berger et al, 2012 ).…”

Energy Conservation Associated with Ethanol Formation from H 2 and CO 2 in Clostridium autoethanogenum Involving Electron Bifurcation

“…Many bacteria contain a monocarboxylate permease for acetate transportation into the cells when the extracellular pH is high, the acetate concentration is low, and thus the acetic acid concentration is very low (79)(80)(81). This indicates that diffusion of acetic acid into the cells can become rate limiting.…”