The decrease in dsrA abundance observed after 19 months of MP operation was in contrast to the
almost steady presence of sulphate-reducing bacteria noted after 13 months of MP operation (5.54% ± 0.3% of total reads). However,the obtained results are consistent with the suggestion that
sulphate-reducing bacteria may exhibit high metabolic flexibility depending on the environmental conditions (Muyzer and Stams,2008).