Monitoring the denitrifying Hyphomicrobium DNA/DNA hybridization group HG 27 in activated sludge and lake water using MPN cultivation and subsequent screening with the gene probe Hvu-1.

Gene probe Hvu-1 is specific for the Hyphomicrobium DNA/DNA-hybridization group HG 27. This group is one of the dominant populations of denitrifying hyphomicrobia in the activated sludge of the sewage treatment plant Plön. The wastewater treatment process of this treatment plant can be characterized as a combination of simultaneous and intermittent nitrification and denitrification. Using this specific probe Hvu-1 (combined with the most-probable-number method and colony hybridization) the abundance of this denitrifying Hyphomicrobium population in activated sludge and in the adjacent receiving Lake Kleiner Plöner See was investigated as a subfraction of total facultatively anaerobic hyphomicrobia. A 15-month monitoring of the activated sludge and of the lake water was conducted to determine temporal variations of the occurrence of this specific population. During the sampling period total facultatively anaerobic hyphomicrobia remained very constant over a year (9 x 10(4) to 6 x 10(5) ml-1). The population of the denitrifying Hyphomicrobium DNA/DNA-hybridization group HG 27 amounted to approximately 30% of the total facultatively anaerobic hyphomicrobia found in the activated sludge. Significant correlations to environmental background parameters or seasonal variations of this population were not found. Furthermore, this specific denitrifying Hyphomicrobium population has no importance for the lake ecosystem.