This article presents Validation List No. 83 from the International Journal of Systematic and Evolutionary Microbiology, which formally validates nine new bacterial species names that were previously published elsewhere. The list includes one new species of methanotroph, Methylomicrobium buryatense, and eight new species of ammonia-oxidizing bacteria in the genus Nitrosomonas. The validation process ensures these names are officially recognized in bacteriological nomenclature. Each entry includes the proposed name, the authors who originally described the organism, and the nomenclatural type strain with its collection deposit information. The document clarifies that the valid publication date is the date of this validation list, not the original publication date. Importantly, validation does not constitute taxonomic acceptance but rather makes the names available for use in scientific nomenclature. The ammonia-oxidizing bacteria represent diverse ecological niches, including halophilic, oligotrophic, and estuarine variants, while the methanotroph was isolated from soda lakes in Russia.

Key findings

• Nine new bacterial species were formally validated: one Methylomicrobium buryatense and eight Nitrosomonas species
• The eight Nitrosomonas species represent ammonia-oxidizing bacteria adapted to diverse environments including marine, estuarine, and salt-tolerant habitats
• Validation date is officially the date of the validation list publication, not the original species description date
• Each species has designated type strains deposited in international culture collections for reference purposes