Iron oxidation by Salmonella enterica serovar Typhimurium strain SL1344 is an abiotic byproduct of nitrate respiration

Price, Alex, Kingston, Ryan, Rowley, Gary, Olsson-Francis, Karen and Macey, Michael C. (2025) Iron oxidation by Salmonella enterica serovar Typhimurium strain SL1344 is an abiotic byproduct of nitrate respiration. Access Microbiology, 7 (12). ISSN 2516-8290

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Abstract

Background: Nitrate-dependent iron (Fe2+) oxidation (NDFO) is an important biogeochemical process, but whether NDFO provides a direct metabolic benefit to facultative anaerobes with diverse lifestyles, such as Salmonella enterica, and what role the respiratory nitrate reductases play in this process is unknown. Methods: This study investigated NDFO in S. enterica serovar Typhimurium strain SL1344. We compared the WT strain with a ∆narGHIJ ∆narZYW mutant (∆nar), which lacks the primary respiratory nitrate reductase (Nar). Cultures were grown anaerobically in lysogeny broth medium amended with 4 mM nitrate and 10 mM FeSO4 as defined nitrate and iron sources. Growth, nitrate depletion, nitrite accumulation, and Fe2+ oxidation were monitored over 14 days. Abiotic controls amended with either nitrate or nitrite were included to control for abiotic iron oxidation.  Results: There was no significant difference in the growth rate and biomass production between the WT and ∆nar strains. However, there was significant variation in nitrite reduction and iron oxidation. 56.9% of the nitrate was depleted from the growth medium (initially 4 mM) with the WT cultures compared to 19.7% with the ∆nar strain. Fe2+ oxidation in the WT cultures reached a Fe2+/Fe total ratio of ~0.52–0.61 during exponential growth and was consistent during the stationary phase, whereas for the mutant, the maximum Fe2+/Fe total ratio was ~0.78, which returned to a more reduced state in stationary phase (Fe2+/ Fe total ~0.95). Abiotic controls amended with nitrite showed rapid Fe2+ oxidation, highlighting the role of nitrite as an oxidant.  Conclusion: The respiratory nitrate reductases are the primary drivers of NDFO in S. enterica SL1344 and are required for the generation of nitrite, which then abiotically oxidizes Fe2+ to Fe3+. This did not confer a growth advantage, suggesting NDFO is an indirect consequence of nitrate respiration rather than a direct energy-conserving pathway in this organism.

Item Type:	Article
Additional Information:	Data Summary: The data supporting the conclusions of this study are provided within the manuscript and the thesis of Dr. Alex Price (2020), titled ‘Microbial Nitrate Dependent Fe Oxidation: A Potential Early Mars Metabolism’, available on the Open University Repository Online at https://oro.open.ac.uk/72495/. This includes the results of the Bradford assay, nitrate, nitrite and iron concentration and speciation data and photographic logs of the cultures over the experiment.
Uncontrolled Keywords:	iron,nitrate,microbiology,microbiology (medical) ,/dk/atira/pure/subjectarea/asjc/2400/2404
Faculty \ School:	Faculty of Science > School of Biological Sciences
Related URLs:	http://www.scopus.com/inward/record.url?...
Depositing User:	LivePure Connector
Date Deposited:	04 Mar 2026 15:30
Last Modified:	04 Mar 2026 15:30
URI:	https://ueaeprints.uea.ac.uk/id/eprint/102181
DOI:	10.1099/acmi.0.001078.v3

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