Changes in Microbial Biofilm Communities during Colonization of Sewer Systems

Abstract

ABSTRACT The coexistence of sulfate-reducing bacteria (SRB) and methanogenic archaea (MA) in anaerobic biofilms developed in sewer inner pipe surfaces favors the accumulation of sulfide (H 2 S) and methane (CH 4 ) as metabolic end products, causing severe impacts on sewerage systems. In this study, we investigated the time course of H 2 S and CH 4 production and emission rates during different stages of biofilm development in relation to changes in the composition of microbial biofilm communities. The study was carried out in a laboratory sewer pilot plant that mimics a full-scale anaerobic rising sewer using a combination of process data and molecular techniques (e.g., quantitative PCR [qPCR], denaturing gradient gel electrophoresis [DGGE], and 16S rRNA gene pyrotag sequencing). After 2 weeks of biofilm growth, H 2 S emission was notably high (290.7 ± 72.3 mg S-H 2 S liter −1 day −1 ), whereas emissions of CH 4 remained low (17.9 ± 15.9 mg COD-CH 4 liter −1 day −1 ). This contrasting trend coincided with a stable SRB community and an archaeal community composed solely of methanogens derived from the human gut (i.e., Methanobrevibacter and Methanosphaera ). In turn, CH 4 emissions increased after 1 year of biofilm growth (327.6 ± 16.6 mg COD-CH 4 liter −1 day −1 ), coinciding with the replacement of methanogenic colonizers by species more adapted to sewer conditions (i.e., Methanosaeta spp.). Our study provides data that confirm the capacity of our laboratory experimental system to mimic the functioning of full-scale sewers both microbiologically and operationally in terms of sulfide and methane production, gaining insight into the complex dynamics of key microbial groups during biofilm development.