Microbial community dynamics in mesophilic and thermophilic batch reactors under methanogenic, phenyl acid-forming conditions

Abstract

Background: Proteinaceous wastes exhibit high theoretical methane yields and their residues are considered valuable fertilisers. The routine anaerobic degradation of proteins often raises problems like high aromatic compound concentrations caused by the entry of aromatic amino acids into the system. A profound investigation of the consequences of aromatic compound exposure on various microorganisms, which cascade-like and interdependently degrade complex molecules to biogas, is still pending. Results: In mesophilic samples, methane was predominantly produced via acetoclastic methanogenesis. The highest positive correlation was observed between phenylacetate (PAA) and Psychrobacter spp. and between phenylpropionate (PPA) and Haloimpatiens spp. Moreover, Syntrophus spp. negatively correlated with PAA (Spearman's rank correlations coefficient (rs) = − 0.46, p < 0.05) and PPA concentrations (rs = − 0.44, p < 0.05) and was also associated with anaerobic benzene ring cleavage. In thermophilic samples, acetate was predominantly oxidised by Tepidanaerobacter spp. or Syntrophaceticus spp. in syntrophic association with a hydrogenotrophic methanogen. The genera Sedimentibacter and Syntrophaceticus correlated positively with both PAA and PPA concentrations. Moreover, Sedimentibacter spp., Tepidanaerobacter spp., Acetomicrobium spp., and Sporanaerobacter spp. were significant LEfSe (linear discriminant analysis effect size) biomarkers for high meso-as well as thermophilic phenyl acid concentrations. Direct negative effects of phenyl acids on methanogenic properties could not be proven. Conclusions: Anaerobic phenyl acid formation is not restricted to specific microbial taxa, but rather done by various meso-and thermophilic bacteria. The cleavage of the highly inert benzene ring is possible in methanogenic batch reactors-at least in mesophilic fermentation processes. The results indicated that phenyl acids rather affect microorganisms engaged in preceding degradation steps than the ones involved in methanogenesis.

Lignin intermediates lead to phenyl acid formation and microbial community shifts in meso- and thermophilic batch reactors

“…are two typical syntrophic acetate oxidising bacteria in methanogenic systems [4,10]. In previous studies, the type of (proteinaceous) substrate determined which of these two SAOBs was dominating [21]. In the present study, the extent of the overload of the lignin intermediates had a strong influence (Fig.…”

“…Even when the pH temporarily dropped to slightly acidic conditions (pH 6.0-6.5, Additional file 1: Table S1), a pure effect of pH Only LEfSe biomarkers with a linear discriminant analysis (LDA) score of 4 or higher are depicted. Genera in bold were previously associated with phenyl acid formation in a study using protein-rich substrates [21] Core microbiome LEfSe biomarker (LDA score ≥ 4) Only LEfSe biomarkers with an LDA score of 4 or higher are presented. Genera in bold were previously associated with phenyl acid formation in a study using proteinrich substrates [21] Core microbiome LEfSe biomarker (LDA score ≥ 4) due to the lignin intermediate addition is unlikely: While methane formation was indeed restricted in ferulic and coumaric acid MCL samples (Fig.…”

“…Genera in bold were previously associated with phenyl acid formation in a study using protein-rich substrates [21] Core microbiome LEfSe biomarker (LDA score ≥ 4) Only LEfSe biomarkers with an LDA score of 4 or higher are presented. Genera in bold were previously associated with phenyl acid formation in a study using proteinrich substrates [21] Core microbiome LEfSe biomarker (LDA score ≥ 4) due to the lignin intermediate addition is unlikely: While methane formation was indeed restricted in ferulic and coumaric acid MCL samples (Fig. 1), gallic, syringic, and vanillic acid MCL even produced more methane than the control (thus > 85 NmL CH 4 ).…”

“…More recently, genera like Acetomicrobium spp., Sedimentibacter spp., Tepidanaerobacter spp., or Sporanaerobacter spp. were shown to be important biomarkers for high phenyl acid concentrations in batch reactors fed with aromatic amino acids [21]. Whether these genera are directly or indirectly associated with phenyl acid formation remains to be elucidated.…”

“…Whether these genera are directly or indirectly associated with phenyl acid formation remains to be elucidated. The thermodynamically difficult cleavage of the benzene ring itself seemed to be more efficient at mesothan at thermophilic temperatures-at least in batch reactors [21]. However, the preceding study focused on the degradation of aromatic amino acids (deriving from proteinaceous materials); a closer look on the degradation of lignin intermediates in terms of phenyl acid formation as well as microbial community dynamics is still missing.…”