A Gram-negative, aerobic, non-motile and non-spore forming bacterium, designated strain SYSU WZ-2(T), was isolated from an estuarine seawater sample. Growth of strain SYSU WZ-2(T) was observed at temperature range of 10-40 degrees C (optimum, 32 degrees C), pH range of 6-10 (optimum, pH 7-8) and in the presence of up to 5.0% NaCl(w/v). The DNA G+C content of the novel strain was determined to be 30.1% (genome). The major polar lipids were found to be diphosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine, an unidentified aminolipid, two unidentified aminophospholipids and two unidentified phospholipids. The major fatty acids were C-18:0 3-OH (27.5%), C(18:1)9c (19.3%), C-16:0 (17.0%) and C-14:0 (12.9%). The respiratory quinone was found to be ubiquinone Q8. Pairwise comparison of the 16S rRNA gene sequence showed that strain SYSU WZ-2(T) shares high identities with members of the genera Francisella (94.8-95.9%) and Allofrancisella (93.8-94.2%). The phylogenetic dendrograms based on 16S rRNA gene sequences with the members of the family Francisellaceae showed that the strain SYSU WZ-2(T) formed a distinct phylogenetic lineage well separated from the members of the genera Francisella and Allofrancisella. MALDI-TOF mass spectrometric analysis also depicted a different profile for strain SYSU WZ-2(T) compared with those of members of the genera Francisella and Allofrancisella. Based on the above results and differences in phenotypic and chemotaxonomic features, strain SYSU WZ-2(T) is characterized to represent a new species of a novel genus, for which the name Pseudofrancisella aestuarii gen. nov., sp. nov. is proposed (type strain SYSU WZ-2(T)=KCTC 52557(T)=CGMCC 1.13718(T)).