A novel, Gram-negative bacterial strain, SUA2^T, isolated from groundwater, was characterized using a polyphasic approach. Cells are Gram-negative, non-spore-forming, straight to curved rods with a single polar flagellum. Strain SUA2^T is oxidase- and catalase-positive and is able to fix nitrogen. Poly-β-hydroxybutyrate storage granules are produced. Dominant fatty acids when grown in R2A and VM ethanol media for 72 h at 37 °C are C_{16 : 0}, C_{16 : 1} ω7c, C_{17 : 0} cyclo, C_{10 : 0} 3-OH, C_{18 : 1} ω7c, C_{12 : 0} and C_{15 : 0}. DNA G+C content is 67.9 mol%. Phenotypic and phylogenetic data indicate that strain SUA2^T is related to, but clearly differentiated from Azospira oryzae. Strain SUA2^T is thus proposed as a novel species of the genus Azospira with the name Azospira restricta sp. nov. The description of the genus Azospira is emended to include the characteristics of this novel species. The type strain of Azospira restricta is SUA2^T (=NRRL B-41660^T=DSM 18626^T=LMG 23819^T).