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Few diazotrophs have been found to belong to the family Cytophagaceae so far. In the present study, a Gram-negative, rodshaped bacterium that forms red colonies, was isolated from sands of the Takalamakan desert. It was designated H4X(T). Phylogenetic and biochemical analysis indicated that the isolate is a new species of the genus Pontibacter. The 16S rRNA gene of H4X(T) displays 94.2-96.8% sequence similarities to those of other strains in Pontibacter. The major respiratory quinone is menaquinone-7 (MK-7). The DNA G+C content is 46.6 mol%. The major cellular fatty acids are iso-C-15:0, C-16:1 omega 5c, summed feature 3 (containing C-16:1 omega 6c and/or C-16:1 omega 7c) and summed feature 4 (comprising anteiso-C17:1B and/or iso-C17:1I). The major polar lipids are phosphatidylethanolamine (PE), one aminophospholipid (APL) and some unknown phospholipids (PLs). It is interesting to see that this bacterium can grow very well in a nitrogen-free medium. PCR amplification suggested that the bacterium possesses at least one type of nitrogenase gene. Acetylene reduction assay showed that H4X(T) actually possesses nitrogen-fixing activity. Therefore, it can be concluded that H4X(T) is a new diazotroph. We thus referred it to as Pontibacter diazotrophicus sp. nov. The type strain is H4X(T) (= CCTCC AB 2013049(T) = NRRL B-59974(T)).