Dissolved iron (Fe2+) has been shown to be enhance dissimilatory nitrate reduction to ammonium (DNRA) relative to denitrification, in estuarine sediments, consistent with proposed Fe2+-DNRA mechanisms. However, despite several studies linking increased DNRA rates to Fe2+ dependent DNRA (Cojean, Lehmann, Robertson, Thamdrup, & Zopfi, 2020; Kessler, Roberts, Bissett, & Cook, 2018; Michiels et al., 2017; Rahman, Roberts, Grace, Kessler, & Cook, 2019; Elizabeth K. Robertson, Roberts, Burdorf, Cook, & Thamdrup, 2016; Elizabeth K Robertson & Thamdrup, 2017), the isolated bacteria from sediments were found to be capable of Fe2+ dependent denitrification but not DNRA in pure cultures enriched with Fe2+ and NO3- (Bryce et al., 2018; Elizabeth K Robertson & Thamdrup, 2017; Straub, Benz, Schink, & Widdel, 1996). Thus, there remains a lack of understanding about the associated changes in the microbial population involved with Fe2+-associated DNRA. Slurry experiments with natural iron rich sediment from Western Port Bay Tooradin, Melbourne, Australia showed Fe2+ and NO3- enhanced DNRA. These slurries were enriched in Lutibacter, belonging to Bacteriodea, and Marinobacter belonging to Gammaproteobacteria. Furthermore, Marinobacter adhaerens, Marinobacter salinus and Sunxiuqinia elliptica belonging to Bacteriodea were isolated and experiments undertaken to measure the relative rates of denitrification and DNRA and the role of Fe2+ and NO3- concentration in mediating this. Whole genome sequencing was also simultaneously undertaken to identify/confirm the molecular basis of the observed processes.