Monitoring of culture purity
Microscopy, culturing and molecular analysis were routinely applied. Samples taken from retentostats were plated on solid agar medium (1.5%, w/v) employing the same medium as used in retentostat cultivation, with acetate as a carbon source. Plates were incubated under oxic or anoxic conditions. The FastDNA SPIN Kit for Soil (MP Biomedicals, USA) was used for DNA extraction from 1 mL of the cell culture. The V3 region of the 16S rRNA gene sequence was amplified using bacterial 16S rRNA primers (forward primer F357 with a 40 bp GC clamp attached at the 5'end and reverse primer R518) . Denaturing gradient gel electrophoresis (DGGE) was performed with a Bio-Rad DCode (Hercules, CA) detection system. The PCR products were loaded onto 1 mm thick polyacrylamide gels containing a 30–55% linear denaturant gradient. Electrophoresis was performed at a constant voltage of 200 V for 200 min in 1× TAE running buffer at 60C . After electrophoresis,the gels were stained with ethidium bromide buffer and photographed under UV light using a Kodak EDAS 290 camera