Chapter 15 - The Ecology of Nitrifying Bacteria

Abstract

This chapter begins with a description of the microbial groups carrying out nitrification and their distribution in major habitats. This is followed by a discussion of the influence of nitrifier physiology, physiological diversity, and environmental factors on their community structure, environmental distribution, activities, and ecosystem function. N2 oxidation in most environments is considered to be dominated by Gram-negative autotrophic N2 oxidizers. Environmental clone sequences suggest the existence of two novel clusters, Nitrosospira cluster 1 and Nitrosomonas cluster 5, which are not currently represented in laboratory cultures. NH3-oxidizing archaea are traditionally associated with extreme environments but the analysis of 16S rRNA environmental clones has demonstrated their abundance in a wide range of ‘non-extreme’," mesophilic environments. NO2-oxidizers have been studied less frequently and biochemical and physiological studies have focused on Nitrobacter. The chapter deals with the community structure of nitrifiers in natural environments. Molecular techniques represent a major advance on cultivation-based methods and it is now possible to study NH3 oxidizer diversity and community composition. Factors influencing the ecology of nitrifying bacteria outlines the enrichment and isolation of the pure cultures of nitrifying bacteria, measurement of nitrification activity, maximum specific growth rate of nitrifiers, affinity of nitrifying bacteria for ammonia and nitrite, inhibition of nitrifiers by high substrate concentration, transformation of carbon compounds by nitrifying bacteria, nitrification at low-oxygen concentrations, starvation mechanisms and biofilm formation, formation of cell aggregates by nitrifying bacteria, influence of salt concentration on nitrifiers, and influence of pH on nitrifier growth and activity.