FIG. 3.

Southern blot hybridization of nirS fragments obtained from environmental samples with the primer combination nirS1F-nirS6R to the digoxigenin-labeled fragment from Pseudomonas stutzeri ZoBell. Lanes: 1 and 8, digoxigenin-labeled DNA size standard VII (Boehringer); 2, sediment from Lake Kleiner Plöner See (15 μl), 3, water from Lake Plussee (12 μl); 4, water from Lake Kleiner Plöner See (20 μl); 5, activated sludge from the sewage treatment plant at Plön (10 μl); 6, enrichment culture for denitrifying methylotrophic bacteria (20 μl); 7, P. stutzeri ZoBell positive control (1 μl).