Isolation and Identification of Salt-tolerant (NaCl) <i>Nitrosomonas</i> Bacteria from Tanned Wastewater Sources

Ammonium-rich and saline wastewater from the tanning industry poses a significant challenge for conventional biological treatment, as high salinity inhibits the activity of nitrifying bacteria. While halotolerant Nitrosomonas strains have been reported in hypersaline environments worldwide, their occurrence and characteristics in Vietnam remain largely unexplored. In this study, salt-tolerant Nitrosomonas strains were isolated from tanning wastewater at Hiep Phuoc Industrial Park, Ho Chi Minh City. Colonies were obtained using Winogradsky medium, and ammonium-oxidizing capacity was confirmed by the Griess-Ilosvay assay. Among the isolates, strain TD2 exhibited superior halotolerance, achieving 53.2% ammonium removal after 72 hours in enrichment medium supplemented with 10 g NaCl L-1, with a maximum cell density of 4.5 × 105 CFU mL-1. Molecular identification based on 16S rRNA gene sequencing revealed 99.39% similarity of TD2 to Nitrosomonas europaea, and phylogenetic analysis confirmed its clustering with salt-tolerant Nitrosomonas clades. This study provides the first report of halotolerant Nitrosomonas isolation from tanning wastewater in Vietnam, highlighting TD2 as a promising candidate for bioaugmentation in partial nitritation-anammox processes for nitrogen removal in saline ammonium-rich effluents.