Competition for Ammonium between Nitrifying and Heterotrophic Bacteria in Dual Energy-Limited Chemostats

Abstract

The absence of nitrification in soils rich in organic matter has often been reported. Therefore, competition for limiting amounts of ammonium between the chemolithotrophic ammonium-oxidizing species Nitrosomonas europaea and the heterotrophic species Arthrobacter globiformis was studied in the presence of Nitrobacter winogradskyi in continuous cultures at dilution rates of 0.004 and 0.01 h-1. Ammonium limitation of A. globiformis was achieved by increasing the glucose concentration in the reservoir stepwise from 0 to 5 mM while maintaining the ammonium concentration at 2 mM. The numbers of N. europaea and N. winogradskyi cells decreased as the numbers of heterotrophic bacteria rose with increasing glucose concentrations for both dilution rates. Critical carbon-to-nitrogen ratios of 11.6 and 9.6 were determined for the dilution rates of 0.004 and 0.01 h-1, respectively. Below these critical values, coexistence of the competing species was found in steady-state situations. Although the numbers were strongly reduced, the nitrifying bacteria were not fully outcompeted by the heterotrophic bacteria above the critical carbon-to-nitrogen ratios. Nitrifying bacteria could probably maintain themselves in the system above the critical carbon-to-nitrogen ratios because they are attached to the glass wall of the culture vessels. The numbers of N. europaea decreased more than did those of N. winogradskyi. This was assumed to be due to heterotrophic growth of the latter species on organic substrates excreted by the heterotrophic bacteria. * Corresponding author. populations, each limited by a different substrate, can coexist in a steady-state situation (13, 40, 45). Hence, below a critical carbon-to-nitrogen ratio, where the heterotrophs are

Competition between heterotrophic and autotrophic nitrifiers for ammonia in chemostat cultures

“…At a C/N ratio of 10.4, T. pantotropha dominated the mixed culture. Similar results were obtained by Verhagen and Laanbrock [27] in a co-culture of N. europaea, Nitrobacter winogradskyi and a heterotroph. They found critical C/N ratios of 12 and 10 at dilution rates of 0.004 h -~ and 0.01 h ~, respectively.…”

Bacterial immobilization and remineralization of N at different growth rates and N concentrations

“…The observation that the ratio between nitrification and NH þ 4 immobilization decreased with increasing NH þ 4 immobilization rates supports results from in situ estimations of nitrification and NH þ 4 immobilization rates [42]. A larger fraction of NH þ 4 seems to be available to nitrifying bacteria when the heterotrophic activity is low [8,14], probably because nitrifying bacteria are inferior competitors with heterotrophic microorganisms for NH þ 4 [8,43,44]. Significant amounts of NH þ 4 were nitrified at the beginning of the incubation at all three NH þ 4 concentrations.…”

Dynamics of ammonia-oxidizing communities in barley-planted bulk soil and rhizosphere following nitrate and ammonium fertilizer amendment

“…Similarly, competition for NH 4 -N was shown to affect the gross nitrification rates negatively in the rhizosphere of wild oat (Herman et al, 2006). Organic carbon (C) or nitrification inhibitors released from plant roots may additionally inhibit autotrophic AOB (Verhagen & Laanbroek, 1991;Strauss & Lamberti, 2000;Subbarao et al, 2007). Besides scavenging ammonium, barley roots appeared to also compete efficiently for nitrate, as has been evidenced previously especially during early barley plant growth stages (Inselsbacher et al, 2010).…”