Temperature influences the population structure of nitrite‐oxidizing bacteria in activated sludge

Activated sludge from the municipal waste water treatment plant in Hamburg was seeded with mineral nitrite medium and incubated at 10°C, 17°C and 28°C. Dominant lithoautotrophic nitrite-oxidizing bacteria have been identified by electron microscopy, denaturing and temperature gradient gel electrophoresis and PCR with genus-specific primer pairs. The results have revealed the existence of three different genera of nitrite-oxidizing bacteria, namely Nitrospira, Nitrobacter and a novel cold-adapted nitrite oxidizer. As shown by electron microscopy members of the novel genus coexisted in activated sludge together with Nitrospira. A temperature-dependent shift in the population structure was demonstrated by cultivation-based approaches. The novel nitrite oxidizer was enriched at temperatures of 10°C and 17°C. Representatives of Nitrospira were able to grow in a broad temperature range between 10°C and 28°C and members of Nitrobacter were enriched during incubations at 17°C and 28°C. By subsequent 16S rDNA sequencing, the cold-adapted nitrite oxidizer was shown to be closely related to the betaproteobacterium 'Candidatus Nitrotoga arctica'. These findings demonstrated that the population structure of nitrite-oxidizing bacteria in activated sludge is more complex than previously thought and responds strongly to long-term temperature changes.