Effect of Sub-Stoichiometric Fe(III) Amounts on LCFA Degradation by Methanogenic Communities

Abstract

Long-chain fatty acids (LCFA) are common contaminants in municipal and industrial wastewater that can be converted anaerobically to methane. A low hydrogen partial pressure is required for LCFA degradation by anaerobic bacteria, requiring the establishment of syntrophic relationships with hydrogenotrophic methanogens. However, high LCFA loads can inhibit methanogens, hindering biodegradation. Because it has been suggested that anaerobic degradation of these compounds may be enhanced by the presence of alternative electron acceptors, such as iron, we investigated the effect of sub-stoichiometric amounts of Fe(III) on oleate (C18:1 LCFA) degradation by suspended and granular methanogenic sludge. Fe(III) accelerated oleate biodegradation and hydrogenotrophic methanogenesis in the assays with suspended sludge, with H2-consuming methanogens coexisting with iron-reducing bacteria. On the other hand, acetoclastic methanogenesis was delayed by Fe(III). These effects were less evident with granular sludge, possibly due to its higher initial methanogenic activity relative to suspended sludge. Enrichments with close-to-stoichiometric amounts of Fe(III) resulted in a microbial community mainly composed of Geobacter, Syntrophomonas, and Methanobacterium genera, with relative abundances of 83–89%, 3–6%, and 0.2–10%, respectively. In these enrichments, oleate was biodegraded to acetate and coupled to iron-reduction and methane production, revealing novel microbial interactions between syntrophic LCFA-degrading bacteria, iron-reducing bacteria, and methanogens.

Enhanced anaerobic digestion of dairy wastewater in a granular activated carbon amended sequential batch reactor

“…Nakasaki et al (2019) stated that Synergistes bacteria enhance the lipid degradation through active acetate degradation, pulling the degradation system forward. Similarly, some species in the Geobacter genus showed existence of genes encoding a long‐chain fatty acyl‐CoA dehydrogenase, FadE, suggesting the potential for LCFA metabolism (Cavaleiro et al, 2020). In addition to Geobacter and Synergistes , the presence and activity of LCFAs degrading bacteria such as Acinetobacter , Arcobacter , Azonexus , Syntrophomonas , Pseudomonas , and Clostridium were observed due to the presence of GAC (Baserba et al, 2012; Ning et al, 2018; Westerholm & Schnürer, 2019; Wongfaed et al, 2020; Zhu et al, 2015).…”

Principles, Advances, and Perspectives of Anaerobic Digestion of Lipids

“…In that study, faster LCFA biodegradation was observed by suspended sludge in the presence of iron, but no noticeable effect of iron was observed with granular sludge. Regarding the microbial community composition, the results obtained suggest the occurrence of a novel microbial interaction in LCFA oxidation, involving microorganisms of the Syntrophomonas, Geobacter , and Methanobacterium genera …”

“…Recently, a new study suggested that the anaerobic degradation of LCFAs could be enhanced by the presence of other electron acceptors such as iron. Cavaleiro et al 128 investigated the effect of different substoichiometric amounts of Fe(III) on the anaerobic degradation of oleate in suspended and granular sludge. In that study, faster LCFA biodegradation was observed by suspended sludge in the presence of iron, but no noticeable effect of iron was observed with granular sludge.…”

“…Regarding the microbial community composition, the results obtained suggest the occurrence of a novel microbial interaction in LCFA oxidation, involving microorganisms of the Syntrophomonas, Geobacter, and Methanobacterium genera. 128 The microbiome of the anaerobic LCFA-degrading communities was initially studied using traditional molecular techniques (e.g., cloning and sequencing), targeting the 16S rRNA gene, focusing on phylogenetic and taxonomic characterizations. 115,129−131 In general, the relative abundance of fatty acid-degrading syntrophic bacteria in high-rate methanogenic bioreactors is low (between 0.2% and 3%), despite their importance in lipids/LCFA degradation.…”

Special Issue “Anaerobes in Biogeochemical Cycles”

“…This Special Issue gathers seven articles on anaerobes with roles in several biogeochemical cycles. One article involves the inorganic carbon cycle [ 4 ], two describe the relationship between predominant physiological types of prokaryotes in marine sediments and propionate and butyrate degradation through sulphate reduction, fermentation, and methanogenesis in marine sediments [ 5 , 6 ], two involve the discovery of novel biodiversity involved in the sulphur cycle [ 7 , 8 ], and two focus on the role of iron in anaerobic methane oxidation [ 9 ] and in the facilitation of anaerobic long chain fatty acid degradation [ 10 ].…”