Ordered Changes in Methane Production Performance and Metabolic Pathway Transition of Methanogenic Archaea under Gradually Increasing Sodium Propionate Stress Intensity

Abstract

This study examined the impact of sodium propionate concentration (0–40 g/L) on the methanogenic archaea in an inoculum which was cultured in basal nutrient medium, exploring its mechanisms and nonlinear stress intensity. The results indicated that at low concentrations, propionate-maintained homeostasis of the anaerobic digestion (AD) system and enriched Methanosaeta. However, when the concentration exceeded 16 g/L, the stability of the AD system was disrupted. The methanogenic pathway shifted towards a predominantly hydrogenotrophic pathway, resulting in a significant increase in methane yield. Below concentrations of 28 g/L, the AD system gradually enhanced its ability to utilize propionate in an orderly manner. At concentrations of 24–28 g/L, genera (e.g., Advenella and Methanosarcina) were enriched to adapt to the high-VFA environment. This was accompanied by a significant upregulation of genes related to the methylotrophic and hydrogenotrophic pathways, effectively mitigating propionate inhibition and enhancing methanogenesis. Conversely, excess concentrations (>30 g/L) suppressed methanogenesis-related genes and led to methane production arrest despite activating specialized propionate-metabolizing bacteria such as genus Pelotomaculum schinkii. As such, an increase in the stress intensity of propionate promotes a change in the metabolic pathways of methanogens and increases methane production; however, excessive sodium propionate was not conducive to maintaining the steady state of the system.