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Abstract

During growth of Methanobacterium thermoautotrophicum in a fed-batch fermentor, the cells are confronted with a steady decrease in the concentration of the hydrogen energy supply. In order to investigate how the organism responds to these changes, cells collected during different growth phases were examined for their methanogenic properties. Cellular levels of the various methanogenic isoenzymes and functionally equivalent enzymes were also determined. Cells were found to maintain the rates of methanogenesis by lowering their affinity for hydrogen: the apparent Km(H2) decreased in going from the exponential to the stationary phase. Simultaneously, the maximal specific methane production rate changed. Levels of H2-dependent methenyl-tetrahydromethanopterin dehydrogenase (H2-MDH) and methyl coenzyme M reductase isoenzyme II (MCR II) decreased upon entry of the stationary phase. Cells grown under conditions that favored MCR II expression had higher levels of MCR II and H2-MDH, whereas in cells grown under conditions favoring MCR I, levels of MCR II were much lower and the cells had an increased affinity for hydrogen throughout the growth cycle. The use of thiosulfate as a medium reductant was found to have a negative effect on levels of MCR II and H2-MDH. From these results it was concluded that M. thermoautotrophicum responds to variations in hydrogen availability and other environmental conditions (pH, growth temperature, medium reductant) by altering its physiology. The adaptation includes, among others, the differential expression of the MDH and MCR isoenzymes.

Method for Indirect Quantification of CH4 Production via H2O Production Using Hydrogenotrophic Methanogens

“…Furthermore, some methanogens are known to metabolize carbon monoxide (Oelgeschläger and Rother, 2009 ; Ferry, 2010 ). A physiological characteristic of methanogens is that they may vary their growth to product yield (Y ( x / CH 4) ) upon experiencing a change in environmental conditions—a mechanism commonly referred to as uncoupling (Mountfort and Asher, 1979 ; Archer, 1985 ; Fardeau and Belaich, 1986 ; Tsao et al, 1994 ; Liu et al, 1999 ; Pennings et al, 2000 ; Ver Eecke et al, 2013 ; Bernacchi et al, 2014 ; Taubner et al, 2015 ).…”

Photochemical Runaway in Exoplanet Atmospheres: Implications for Biosignatures

“…P me can be related to ∆G reac via P me = ∆G reac M , where M is the production rate of the metabolic byproduct in units of mol g −1 s −1 . In studies we reviewed M ≤ 10 −4 mol g −1 s −1 (Müller et al 1986;Patel et al 1978;Patel & Roth 1977;Pennings et al 2000;Perski et al 1981;Schönheit & Beimborn 1985;Takai et al 2008;Zinder & Koch 1984) and we adopt this as our upper limit, providing our second constraint:…”

Assessing the Ecophysiology of Methanogens in the Context of Recent Astrobiological and Planetological Studies

“…Methanogens are well known for a variety of astonishing morphological and ecophysiological features. One of these ecophysiological features is their ability to grow hydrogenotrophically while varying their growth-to-product-yield Y —a mechanism also referred to as uncoupling [ 6 , 10 , 40 , 44 , 72 , 73 , 74 , 75 , 76 , 77 , 78 ]. Uncoupling in methanogens occurs when environmental factors ( i.e.…”

“…As a consequence of changing environmental factors methanogens react rapidly by altering their metabolism redirecting the carbon flux to either biomass formation or to maintaining cellular homoeostasis. As an example it has been found that Methanobacterium thermoautotrophicum responds to variations in H concentration by differentially expressing methenyl-tetrahydromethanopterin dehydrogenase and methyl coenzyme M reductase isoenzymes [ 77 ]. Other examples include the varying Y in Methanothermobacter marburgensis upon exposure to different ammonia concentration or dilution rates [ 40 , 44 ].…”