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. 2020 Sep 7;8(9):1375.
doi: 10.3390/microorganisms8091375.

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

Ana J Cavaleiro  1 , Ana P Guedes  1 , Sérgio A Silva  1 , Ana L Arantes  1 , João C Sequeira  1 , Andreia F Salvador  1 , Diana Z Sousa  1   2 , Alfons J M Stams  1   2 , M Madalena Alves  1
Affiliations

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

Ana J Cavaleiro et al. Microorganisms. .

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.

Keywords: Fe(III); Geobacter; Syntrophomonas; long chain fatty acids; methanogenesis; oleate.

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Conflict of interest statement

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

Figures

Figure 1
Figure 1
Scheme of the experimental procedure applied: oleate biodegradation with sub-stoichiometric Fe(III) concentration (a) and enrichment cultures (b). SS—suspended sludge; GS—granular sludge; M—methanogenic assays; IR—Fe(III)-reducing assays; OL—oleate; Blk—blank assays (no added carbon source); Abiotic Ctr—abiotic controls (without inoculum).
Figure 2
Figure 2
Biodegradation assays performed with sub-stoichiometric Fe(III) concentration: acetate (a,b), Fe(II) (c,d), and methane (e,f) concentrations measured in the assays inoculated with suspended or granular sludge, respectively. Open symbols were used for the blanks.
Figure 3
Figure 3
Fe(II) (●) (a), and acetate (○) and methane (▲) (b) concentrations measured during the incubation of culture GS(5) with oleate and Fe(OH)3.
See this image and copyright information in PMC

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