Competition between Nitrospira spp. and Nitrobacter spp. in nitrite-oxidizing bioreactors

Area of Science:

• Microbial Ecology
• Environmental Microbiology
• Wastewater Treatment

Background:

• Nitrite-oxidizing bacteria are crucial for nitrogen removal in wastewater treatment.
• The competitive dynamics between Nitrobacter spp. and Nitrospira spp. are increasingly recognized in activated sludge systems.
• Understanding these interactions is key to optimizing nitrification processes.

Purpose of the Study:

• To investigate the effect of nitrite concentrations on the competition between Nitrobacter spp. and Nitrospira spp.
• To determine if nitrite availability influences the dominance of these bacterial groups in activated sludge.
• To explore the stability of competitive dominance under varying nitrite conditions.

Main Methods:

• Utilized two parallel chemostats inoculated with nitrifying activated sludge.
• Introduced Nitrobacter spp. and manipulated nitrite concentrations in one chemostat.
• Quantified relative cellular area of Nitrobacter and Nitrospira using fluorescence in situ hybridization (FISH).

Main Results:

• Elevated nitrite concentrations stimulated Nitrobacter growth, leading to its dominance.
• Nitrospira spp. dominated in the control chemostat with constant, lower nitrite levels.
• The dominance of Nitrobacter, once established by high nitrite, persisted even after nitrite levels were reduced.

Conclusions:

• Nitrobacter spp. are superior competitors under high nitrite (abundant resource) conditions.
• Nitrospira spp. thrive under low nitrite (scarce resource) conditions.
• Established Nitrobacter dominance may be persistent, potentially due to growth inhibition of Nitrospira or insufficient experimental duration.