Australian Centre for Water
and Environmental Biotechnology

Project Dates: 2012 to 2016


There are a number of applications in which free nitrous acid (FNA), the protonated form of nitrite (HNO2), is used as an antimicrobial agent due to its bacteriostatic and bactericidal effects on a range of microbes. However, details of the antimicrobial mechanisms of FNA are largely unknown. Such details are important for optimizing the application of FNA and for understanding possible resistance to the agent. The overall objective of this research is to elucidate the responses of various microbes such as Psuedomonas aeruginosa PAO1 (P. aeruginosa), Desulfovibrio vulgaris Hildenborough (D. vulgaris) as well as determining the responses of organisms directly in mixed culture activated sludge used in wastewater treatment. The project aims to determine the microbial molecular and physiological mechanisms that may contribute to tolerance and resistance to FNA exposure. The outcome of these studies will improve our understanding of microbial responses to FNA, and contribute towards improved control of sewer corrosion and odor management in wastewater treatment.

Another potential application of FNA is for control of nitrifying microorganisms in wastewater treatment systems. The activated sludge process is used in nitrogen removal from wastewater. The nitrifying bacterial community in the activated sludge of wastewater treatment processes contain the Ammonia oxidising bacteria (AOB) and the Nitrite oxidising bacteria (NOB). Nitrite is produced by AOB through the oxidation of ammonia. In a nitrifying bacterial community FNA exerts a stronger biocidal effect on the NOB than AOB. The reason for this for this difference in tolerance is unknown especially considering NOB has the molecular pathways/mechanisms by which it can tolerate higher nitrite concentrations. The removal of NOB from the activated sludge system is beneficial for wastewater treatment since it saves on running costs. We study the effects of FNA on nitrifying community i.e. both AOB and NOB on exposure to FNA using metagenomics and SWATH metaproteomics techniques.  


  • Associate Prof. Paul Wilmes, Université Du Luxembourg
  • Professor Philip Hugenholtz, Australian Centre for Ecogenomics, University of Queensland
  • Professor David Richardson, University of East Anglia.