title: Exogenous nitrate attenuates nitrite toxicity to anaerobic ammonium oxidizing (anammox) bacteria.
abstract: Anaerobic ammonium oxidizing bacteria (anammox) can be severely inhibited by one of its main substrates, nitrite (NO2(-)). At present, there is limited information on the processes by which anammox bacteria are able to tolerate toxic NO2(-). Intracellular consumption or electrochemically driven (transmembrane proton motive force) NO2(-) export are considered the main mechanisms of NO2(-) detoxification. In this work, we evaluated the potential of exogenous nitrate (NO3(-)) on relieving NO2(-) toxicity, putatively facilitated by NarK, a NO3(-)/NO2(-) transporter encoded in the anammox genome. The relative contribution of NO3(-) to NO2(-) detoxification was found to be pH dependent. Exposure of anammox cells to NO2(-) in absence of their electron donating substrate, ammonium (NH4(+)), causes NO2(-) stress. At pH 6.7 and 7.0, the activity of NO2(-) stressed cells was respectively 0 and 27% of the non-stressed control activity (NO2(-) and NH4(+) fed simultaneously). Exogenous NO3(-) addition caused the recovery to 42% and 80% of the control activity at pH 6.7 and 7.0, respectively. The recovery of the activity of NO2(-) stressed cells improved with increasing NO3(-) concentration, the maximum recovery being achieved at 0.85 mM. The NO3(-) pre-incubation time is less significant at pH 7.0 than at pH 6.7 due to a more severe NO2(-) toxicity at lower pH. Additionally, NO3(-) caused almost complete attenuation of NO2(-) toxicity in cells exposed to the proton gradient disruptor carbonyl cyanide m-chlorophenyl hydrazone at pH 7.5, providing evidence that the NO3(-) attenuation is independent of the proton motive force. The absence of a measurable NO3(-) consumption (or NO3(-) dependent N2 production) during the batch tests leaves NO3(-) dependent active transport of NO2(-) as the only plausible explanation for the relief of NO2(-) inhibition. We suggest that anammox cells can use a secondary transport system facilitated by exogenous NO3(-) to alleviate NO2(-) toxicity.
authors.affiliation: Department of Chemical and Environmental Engineering, University of Arizona, 1133 E. James E. Rogers Way, Tucson, AZ 85721-001, USA. Electronic address: guangbinli@email.arizona.edu.
authors.forename: Guangbin
authors.initials: G
authors.lastname: Li
authors.affiliation: Department of Chemical and Environmental Engineering, University of Arizona, 1133 E. James E. Rogers Way, Tucson, AZ 85721-001, USA.
authors.forename: David
authors.initials: D
authors.lastname: Vilcherrez
authors.affiliation: Department of Chemical and Environmental Engineering, University of Arizona, 1133 E. James E. Rogers Way, Tucson, AZ 85721-001, USA.
authors.forename: Jose Maria
authors.initials: JM
authors.lastname: Carvajal-Arroyo
authors.affiliation: Department of Chemical and Environmental Engineering, University of Arizona, 1133 E. James E. Rogers Way, Tucson, AZ 85721-001, USA.
authors.forename: Reyes
authors.initials: R
authors.lastname: Sierra-Alvarez
authors.affiliation: Department of Chemical and Environmental Engineering, University of Arizona, 1133 E. James E. Rogers Way, Tucson, AZ 85721-001, USA.
authors.forename: Jim A
authors.initials: JA
authors.lastname: Field
mesh_terms: D064751:Ammonium Compounds / Q000378:metabolism; D001421:Bacteria, Anaerobic / Q000378:metabolism*; D009566:Nitrates / Q000494:pharmacology*; D009573:Nitrites / Q000633:toxicity*; D010084:Oxidation-Reduction
chemical_list: D064751:Ammonium Compounds; D009566:Nitrates; D009573:Nitrites
keywords: Detoxification; Mechanism; Nitrate; Nitrite inhibition; Nitrogen removal