A Gram-stain-negative, non-motile and coccoid, ovoid or rod-shaped bacterial strain, OITF-57(T), which was isolated from a tidal flat sediment in South Korea, was characterized taxonomically. Strain OITF-57(T) grew optimally at 25 degrees C, at pH 7.0-8.0 and in the presence of 2.0% (w/v) NaCl. Strain OITF-57(T) exhibited the highest 16S rRNA gene sequence similarity value (94.2%) to the type strain of Pontivivens insulae forming a cluster in the neighbour-joining phylogenetic tree. In the maximum-likelihood and maximum-parsimony phylogenetic trees based on 16S rRNA gene sequences and the phylogenetic tress based on gyrB sequences, strain OITF-57(T) formed evolutionary lineages independent of those of other taxa. Strain OITF-57(T) contained Q-10 as the predominant ubiquinone and C-18:1 omega 7c as the major fatty acid. The major polar lipids of strain OITF-57(T) were phosphatidylcholine and phosphatidylglycerol. The DNA G + C content of strain OITF-57(T) was 66.0 mol%. The chemotaxonomic data and other differential phenotypic properties made it possible to distinguish strain OITF-57(T) from the genus Pontivivens and other phylogenetically related genera. On the basis of the data presented, strain OITF-57(T) constitutes a new genus and species within the class Alphaproteobacteria, for which the name Pseudopontivivens aestuariicola gen. nov., sp. nov. is proposed. The type strain is OITF-57(T) (= KACC 19570(T) = CGMCC 1.13481(T)).