Comparison of Oxidation Kinetics of Nitrite-Oxidizing Bacteria: Nitrite Availability as a Key Factor in Niche Differentiation

Abstract

Nitrification has an immense impact on nitrogen cycling in natural ecosystems and in wastewater treatment plants. Mathematical models function as tools to capture the complexity of these biological systems, but kinetic parameters especially of nitriteoxidizing bacteria (NOB) are lacking because of a limited number of pure cultures until recently. In this study, we compared the nitrite oxidation kinetics of six pure cultures and one enrichment culture representing three genera of NOB (Nitrobacter, Nitrospira, Nitrotoga). With half-saturation constants (K m ) between 9 and 27 M nitrite, Nitrospira bacteria are adapted to live under significant substrate limitation. Nitrobacter showed a wide range of lower substrate affinities, with K m values between 49 and 544 M nitrite. However, the advantage of Nitrobacter emerged under excess nitrite supply, sustaining high maximum specific activities (V max ) of 64 to 164 mol nitrite/mg protein/h, contrary to the lower activities of Nitrospira of 18 to 48 mol nitrite/mg protein/h. The V max (26 mol nitrite/mg protein/h) and K m (58 M nitrite) of "Candidatus Nitrotoga arctica" measured at a low temperature of 17°C suggest that Nitrotoga can advantageously compete with other NOB, especially in cold habitats. The kinetic parameters determined represent improved basis values for nitrifying models and will support predictions of community structure and nitrification rates in natural and engineered ecosystems.A erobic nitrite oxidation is the second microbially mediated part of nitrification, a key process in the global nitrogen cycle, catalyzed by autotrophic, slow-growing nitrite-oxidizing bacteria (NOB). Under nitrifying conditions, the growth of NOB is directly linked to the nitrite production rate and the kinetics of nitrite oxidation (1). Nitrification occurs in almost every aquatic and terrestrial ecosystem, in natural as well as in artificial environments like wastewater treatment plants (WWTPs). The intermediate nitrite hardly accumulates, but local or temporary peaks might appear especially when conditions suddenly change or adverse conditions like alkaline pH values impair NOB activity (2). In WWTPs, disturbances can cause nitrite peaks after destabilization of the NOB guild (3). In soils, nitrite concentrations can vary from ϳ0.01 to ϳ100 g of nitrogen g of soil Ϫ1 , with the highest values measured in fertilized samples (4). Therefore, the concentration of nitrite as the substrate of NOB varies and is regarded as one major factor providing niche differentiation (5). In the ecological context, field studies are important to characterize nitrifying communities with specific activities and affinities for nitrite, but for a better understanding of wastewater treatment processes, mathematical models are required (6). Such models include ecophysiological kinetic data, which are known primarily for ammonia-oxidizing bacteria (AOB) (7). They provide the substrate nitrite for the second major step of nitrification. However, the development of two-step nitrification models also ...

A robust nitrifying community in a bioreactor at 50 °C opens up the path for thermophilic nitrogen removal

“…In particular, the specific rates for AOAs range from 11 to 24 μg N mg − 1 protein h − 1 (Kim et al, 2012), whereas reported rates for Nitrospira spp. range between 16 and 42 μg N mg − 1 protein h − 1 (Nowka et al, 2015). Interesting differences in substrate/product tolerances were observed.…”

Oxidation kinetics and inverse isotope effect of marine nitrite-oxidizing isolates

“…So far, investigations on nitrite oxidation kinetics have mainly been based on non-marine pure cultures, enrichment cultures, or natural assembles (Prosser 1989, Both et al 1992, Laanbroek et al 1994, Schramm et al 1999, Blackburne et al 2007, Nowka et al 2015. The aim of this study was to investigate the substrate affinity of marine NOB to link it to environmental conditions and nitrite oxidation kinetics, which thus far has been difficult because nitrite affinity of marine NOB had not yet been investigated in pure cultures.…”

“…Nitrite oxidation kinetics were calculated based on activity measurements performed after Nowka et al (2015). Nitrospira sp.…”

Expanded metabolic versatility of ubiquitous nitrite-oxidizing bacteria from the genus Nitrospira

“…Analyses of Nitrobacter genome sequences provided first insights into the genomic makeup of NOB and revealed a greater metabolic flexibility than anticipated earlier, which included the mixotrophic utilization of various organic substrates (8,9). However, Nitrobacter require high nitrite concentrations (10,11), and molecular surveys indicated that Nitrobacter are not the primary NOB in ecosystems with low ambient nitrite levels such as unfertilized soils (12), freshwater habitats (13), and most WWTPs (14).…”

“…Nitrospira are well adapted to low nitrite concentrations (10,11) and form at least six phylogenetic lineages (15,16) that are globally distributed in soils (17,18), the oceans (19), freshwater habitats (20), hot springs (16), and many other oxic habitats (15). In addition, Nitrospira members are the key NOB in most WWTPs (14,15).…”