Analysis of Microbial Community during Biofilm Development in an Anaerobic Wastewater Treatment Reactor

The formation, structure, and biodiversity of a multispecies anaerobic biofilm inside an Upflow Anaerobic Sludge Bed (UASB) reactor fed with brewery wastewater was examined using complementary microbial ecology methods such us fluorescence in situ hybridization (FISH), denaturing gradient gel electrophoresis (DGGE), and cloning. The biofilm development can be roughly divided into three stages: an initial attachment phase (0-36 h) characterized by random adhesion of the cells to the surface; a consolidation phase (from 36 h to 2 weeks) defined by the appearance of microcolonies; and maturation phase (from 2 weeks to 2 months). During the consolidation period, proteobacteria with broad metabolic capabilities, mainly represented by members of alpha-Proteobacteria class (Oleomonas, Azospirillum), predominated. Beta-, gamma-, delta- (both syntrophobacteria and sulfate-reducing bacteria) and epsilon- (Arcobacter sp.) Proteobacteria were also noticeable. Archaea first appeared during the consolidation period. A Methanospirillum-like methanogen was detected after 36 h, and this was followed by the detection of Methanosarcina, after 4 days of biofilm development. The mature biofilm displayed a hill and valley topography with cells embedded in a matrix of exopolymers where the spatial distribution of the microorganisms became well-established. Compared to the earlier phases, the biodiversity had greatly increased. Although alpha-Proteobacteria remained as predominant, members of the phyla Firmicutes, Bacteroidete, and Thermotogae were also detected. Within the domain Archaea, the acetoclastic methanogen Methanosaeta concilii become dominant. This study provides insights on the trophic web and the shifts in population during biofilm development in an UASB reactor.