Facultative anaerobic bacteria enable syntrophic fatty acids degradation under micro-aerobic conditions
Carla Pereira Magalhães, M. Salomé Duarte, M. A. Pereira, Alfons J. M. Stams, A. J. Cavaleiro
Abstract
• Low oxygen concentrations (0.5%) inhibit the activity of syntrophic co-cultures. • With Pseudomonas , syntrophic cultures converted fatty acids to CH 4 , at O 2 up to 2%. • Pseudomonas spp. play a crucial role in mitigating oxygen toxicity. • Facultative anaerobes (FAB) enable resilient and functional syntrophic consortia. • FAB’s activity is more relevant for less easy-to-degrade substrates. Trace amounts of oxygen stimulate facultative anaerobic bacteria (FAB) within anaerobic bioreactors, which was shown to correlate with enhanced methane production from long-chain fatty acids. The relationship between FAB and fatty acid-degrading syntrophic communities under micro-aerobic conditions is still unclear. In this work, two syntrophic co-cultures, Syntrophomonas wolfei + Methanospirillum hungatei and Syntrophomonas zehnderi + Methanobacterium formicicum , were assembled and incubated with short, medium and long-chain fatty acids, with 0–10 % O 2 , in the presence and absence of FAB, here represented by Pseudomonas spp. Without Pseudomonas , the syntrophic activity was inhibited by 79 % at 0.5 % O 2 , but with Pseudomonas , the syntrophic co-cultures successfully converted the fatty acids to methane with up to 2 % O 2 . These findings underscore the pivotal role of FAB in the protection of syntrophic fatty acid-degrading communities under micro-aerobic conditions and emphasizes its significance in real-scale anaerobic digesters where strictly anaerobic conditions may not consistently be maintained.