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Front. Microbiol. | doi: 10.3389/fmicb.2018.00280

Physiological and metagenomic characterizations of the synergistic relationships between ammonia- and nitrite-oxidizing bacteria in freshwater nitrification

 Mingwei CAI1, Siu K. Ng1,  Chee Kent Lim1, Hongyuan Lu1,  Yangyang JIA1 and  Patrick K. Lee1*
  • 1School of Energy and Environment, City University of Hong Kong, Hong Kong

Nitrification plays a crucial role in global nitrogen cycling and treatment processes. However, the relationships between the nitrifier guilds of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) are still poorly understood, especially in freshwater habitats. This study examined the physiological interactions between the AOB and NOB present in a freshwater aquarium biofilter by culturing them, either together or separately, in a synthetic medium. Metagenomic and 16S rRNA gene sequencing revealed the presence and the draft genomes of Nitrosomonas-like AOB as well as Nitrobacter-like NOB in the cultures, including the first draft genome of Nitrobacter vulgaris. The nitrifiers exhibited different growth rates with different ammonium (NH4+) or nitrite concentrations (50 to 1,500 μM) and the growth rates were elevated under a high bicarbonate (HCO3-) concentration. The half-saturation constant (Ks for NH4+), the maximum growth rate (μmax), and the lag duration indicated a strong dependence on the synergistic relationships between the two guilds. Overall, the ecophysiological and metagenomic results in this study provided insights into the phylogeny of the key nitrifying players in a freshwater biofilter and showed that interactions between the two nitrifying guilds in a microbial community enhanced nitrification.

Keywords: freshwater, Biofilter, ammonia-oxidizing bacteria, nitrite-oxidizing bacteria, Synergistic relationships, Metagenomics

Received: 14 Nov 2017; Accepted: 07 Feb 2018.

Edited by:

Chris Francis, Stanford University, United States

Reviewed by:

Lisa Y. Stein, University of Alberta, Canada
Annette Bollmann, Miami University, United States  

Copyright: © 2018 CAI, Ng, Lim, Lu, JIA and Lee. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Patrick K. Lee, City University of Hong Kong, School of Energy and Environment, Kowloon, Hong Kong, patrick.kh.lee@cityu.edu.hk