Limitation of syntrophic coculture growth by the acetogen

Abstract

The syntrophic cooperation between hydrogen-producing acetogens and hydrogenotrophic methanogens relies on a critical balance between both partners. A recent study, provided several indications for the dependence of the biomass-specific growth rate of a methanogenic coculture on the acetogen. Nevertheless, final experimental proof was lacking since biomass-specific rates were obtained from a descriptive model, and not from direct measurement of individual biomass concentrations. In this study, a recently developed quantitative PCR approach was used to measure the individual biomass concentrations in the coculture of Desulfovibrio sp. G11 and Methanospirillum hungatei JF1 on lactate, formate or both. The model-derived growth yields and biomass-specific rates were successfully validated. Experimental findings identified the acetogen as the growth-limiting partner in the coculture on lactate. While the acetogen was operating at its maximum biomass-specific lactate consumption rate, the hydrogenotrophic methanogen showed a significant overcapacity. Furthermore, this study provides experimental evidence for different growth strategies followed by the syntrophic partners in order to maintain a common biomass-specific growth rate. During syntrophic lactate conversion, the biomass-specific electron transfer rate of Methanospirillum hungatei JF1 was three-fold higher compared to Desulfovibrio sp. G11. This is to compensate for the lower methanogenic biomass yield per electron-mole of substrate, which is dictated by the thermodynamics of the underlying reaction.

Enhanced methane production through bioaugmentation of butyrate‐oxidizing hydrogen‐producing acetogens in anaerobic wastewater treatment

“…The glucose solution used contained 5 g of glucose in 1 L water and mixed with 1 g of NH 4 Cl, 0.6 g of NaCl, 0. 2 , 0.5 g of cysteine, 3 g of NaHCO 3 , 2 g of tryptone, 2 g of yeast extract, 0.2 mL of 0.2% resazurin, 10 mL of micronutrient solution, and 10 mL of vitamin solution. The organic wastewater used was a diluted molasses solution with a COD of 12,700 mg/L, to which NH 4 Cl and K 2 HPO 4 were added at a COD:N:P ratio of 500:5:1; NaHCO 3 was used to achieve a pH of approximately 7.8-8.0.…”

“…Methane fermentation of organic wastewater is a complex process and depends on a critical factor, namely, balanced action of several microbial populations [1,2]. During anaerobic wastewater treatment, high-molecular weight biopolymers are initially transformed by fermentative bacteria into volatile fatty acids (VFAs), CO 2 , and H 2 .…”

“…During anaerobic wastewater treatment, high-molecular weight biopolymers are initially transformed by fermentative bacteria into volatile fatty acids (VFAs), CO 2 , and H 2 . VFAs, such as propionic acid, butyric acid, and lactic acid, are subsequently oxidized by hydrogen-producing acetogens (HPAs) into acetic acid, CO 2 , and H 2 , and feedback inhibition and thermodynamic restriction of VFAs to hydrolytic acidification are relieved simultaneously [2][3][4][5]. These products (acetic acid, CO 2 , and H 2 ) are finally converted into CH 4 , CO 2 , and H 2 O by methanogens.…”

“…VFAs, such as propionic acid, butyric acid, and lactic acid, are subsequently oxidized by hydrogen-producing acetogens (HPAs) into acetic acid, CO 2 , and H 2 , and feedback inhibition and thermodynamic restriction of VFAs to hydrolytic acidification are relieved simultaneously [2][3][4][5]. These products (acetic acid, CO 2 , and H 2 ) are finally converted into CH 4 , CO 2 , and H 2 O by methanogens. Thus, acidogenesis, hydrogen-producing acetogenesis, and methanogenesis are generally considered the three main phases in anaerobic wastewater treatment [6,7].…”

“…Hydrogen-producing acetogenesis is apparently a rate-limiting step in methanogenesis because bioaugmentation of HPAs during methane production improved not only hydrogen-producing acetogenesis but also hydrolysis/acidogenesis and methanogenesis. INTRODUCTION Methane fermentation of organic wastewater is a complex process and depends on a critical factor, namely, balanced action of several microbial populations [1,2]. During anaerobic wastewater treatment, high-molecular weight biopolymers are initially transformed by fermentative bacteria into volatile fatty acids (VFAs), CO 2 , and H 2 .…”