Piezo-tolerant natural gas-producing microbes under accumulating p CO2

Ralph E F Lindeboom; Seung Gu Shin; Jan Weijma; Jules B van Lier; Caroline M Plugge

doi:10.1186/s13068-016-0634-7

Piezo-tolerant natural gas-producing microbes under accumulating p CO₂

Biotechnol Biofuels. 2016 Nov 4:9:236. doi: 10.1186/s13068-016-0634-7. eCollection 2016.

Authors

Ralph E F Lindeboom^#^{1

2}, Seung Gu Shin^#^{1

2

3}, Jan Weijma¹, Jules B van Lier², Caroline M Plugge⁴

Affiliations

¹ Sub-Department of Environmental Technology, Wageningen University, P.O. Box 8129, 6700 EV Wageningen, The Netherlands.
² Section Sanitary Engineering, Department of Water Management, Faculty of Civil Engineering and Geosciences, Delft University of Technology, P.O. Box 5048, 2600 GA Delft, The Netherlands.
³ School of Environmental Science and Engineering, Pohang University of Science and Technology, 77 Cheongam-ro, Nam-gu, Pohang, Gyeongbuk 37673 South Korea.
⁴ Laboratory of Microbiology, Wageningen University, Stippeneng 4, 6708 WE Wageningen, The Netherlands.

^# Contributed equally.

Abstract

Background: It is known that a part of natural gas is produced by biogenic degradation of organic matter, but the microbial pathways resulting in the formation of pressurized gas fields remain unknown. Autogeneration of biogas pressure of up to 20 bar has been shown to improve the quality of biogas to the level of biogenic natural gas as the fraction of CO₂ decreased. Still, the pCO₂ is higher compared to atmospheric digestion and this may affect the process in several ways. In this work, we investigated the effect of elevated pCO₂ of up to 0.5 MPa on Gibbs free energy, microbial community composition and substrate utilization kinetics in autogenerative high-pressure digestion.

Results: In this study, biogas pressure (up to 2.0 MPa) was batch-wise autogenerated for 268 days at 303 K in an 8-L bioreactor, resulting in a population dominated by archaeal Methanosaeta concilii, Methanobacterium formicicum and Mtb. beijingense and bacterial Kosmotoga-like (31% of total bacterial species), Propioniferax-like (25%) and Treponema-like (12%) species. Related microorganisms have also been detected in gas, oil and abandoned coal-bed reservoirs, where elevated pressure prevails. After 107 days autogeneration of biogas pressure up to 0.50 MPa of pCO₂, propionate accumulated whilst CH₄ formation declined. Alongside the Propioniferax-like organism, a putative propionate producer, increased in relative abundance in the period of propionate accumulation. Complementary experiments showed that specific propionate conversion rates decreased linearly from 30.3 mg g^-1 VS_added day^-1 by more than 90% to 2.2 mg g^-1 VS_added day^-1 after elevating pCO₂ from 0.10 to 0.50 MPa. Neither thermodynamic limitations, especially due to elevated pH₂, nor pH inhibition could sufficiently explain this phenomenon. The reduced propionate conversion could therefore be attributed to reversible CO₂-toxicity.

Conclusions: The results of this study suggest a generic role of the detected bacterial and archaeal species in biogenic methane formation at elevated pressure. The propionate conversion rate and subsequent methane production rate were inhibited by up to 90% by the accumulating pCO₂ up to 0.5 MPa in the pressure reactor, which opens opportunities for steering carboxylate production using reversible CO₂-toxicity in mixed-culture microbial electrosynthesis and fermentation.Graphical abstractThe role of pCO₂ in steering product formation in autogenerative high pressure digestion.

Keywords: Autogenerative high-pressure digestion; CO2-toxicity; Carboxylate platform; Gibbs free energy; Population dynamics; Propionate accumulation; Syntrophy.