<jats:p>Four nitrite-dissimilating strains, isolated from Weser Estuary sediments, were investigated using a polyphasic taxonomic approach. Phylogenetic analysis based on 16S rRNA gene sequences indicated that these strains belong to the ‘<jats:italic>Betaproteobacteria</jats:italic>’ and are related to the genus <jats:italic>Alcaligenes</jats:italic>. The highest level of sequence similarity (100 %) was found with strain M3A (=ATCC 700596), a dimethyl sulfide-producing marine isolate that was included in this study. DNA–DNA hybridizations between the five strains and related <jats:italic>Alcaligenes faecalis</jats:italic> strains confirmed that the former belong to a single and novel species within the genus <jats:italic>Alcaligenes</jats:italic>. The isolates are Gram-negative, motile, rod-shaped cells with a DNA G+C content of about 56 mol%. The whole-cell fatty acid profiles of the isolates were very similar and included C<jats:sub>16 : 0</jats:sub>, C<jats:sub>17 : 0</jats:sub> cyclo, C<jats:sub>18 : 1</jats:sub> <jats:italic>ω</jats:italic>7<jats:italic>c</jats:italic>, summed feature 2 (comprising any combination of C<jats:sub>12 : 0</jats:sub> aldehyde, an unknown fatty acid of equivalent chain length 10·928, C<jats:sub>16 : 1</jats:sub> iso I and C<jats:sub>14 : 0</jats:sub> 3-OH) and summed feature 3 (C<jats:sub>15 : 0</jats:sub> iso 2-OH and/or C<jats:sub>16 : 1</jats:sub> <jats:italic>ω</jats:italic>7<jats:italic>c</jats:italic>) as the major fatty acid components. On the basis of their phylogenetic, genomic and phenotypic properties, the five novel strains can be assigned to the genus <jats:italic>Alcaligenes</jats:italic> as a novel species, for which the name <jats:italic>Alcaligenes aquatilis</jats:italic> sp. nov. is proposed. The type strain is LMG 22996<jats:sup>T</jats:sup> (=CCUG 50924<jats:sup>T</jats:sup>).</jats:p>