We studied the peptide-degrading anaerobic communities of methanogenic reactors from two mesophilic
full-scale modified upflow anaerobic sludge blanket (UASB) reactors treating brewery wastewater in
Colombia. Most probable number (MPN) counts varied between 7.1 x 108 and 6.6 x 109 bacteria/g volatile
suspended solids VSS (Methanogenic Reactor 1) and 7.2 x 106 and 6.4 x 107 bacteria/g (VSS)
(Methanogenic Reactor 2). Metabolites detected in the highest positive MPN dilutions in both reactors
were mostly acetate, propionate, isovalerate and, in some cases, negligible concentrations of butyrate.
Using the highest positive dilutions of MPN counts, 50 dominant strains were isolated from both reactors,
and 12 strains were selected for sequencing their 16S rRNA gene based on their phenotypic characteristics.
The small-subunit rRNA gene sequences indicated that these strains were affiliated to the families
Propionibacteriaceae, Clostridiaceae and Syntrophomonadaceae in the low G + C gram-positive group
and Desulfovibrio spp. in the class d-Proteobacteria. The main metabolites detected in the highest positive
dilutions of MPN and the presence of Syntrophomonadaceae indicate the effect of the syntrophic
associations on the bioconversion of these substrates in methanogenic reactors. Additionally, the potential
utilization of external electron acceptors for the complete degradation of amino acids by Clostridium
strains confirms the relevance of these acceptors in the transformation of peptides and amino acids in these
systems.
