Pontibacter diazotrophicus sp. nov., a Novel Nitrogen-Fixing Bacterium of the Family Cytophagaceae

Few diazotrophs have been found to belong to the family Cytophagaceae so far. In the present study, a Gram-negative, rod-shaped 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)ω5c, summed feature 3 (containing C(16∶1)ω6c and/or C(16∶1)ω7c) and summed feature 4 (comprising anteiso-C(17∶1)B and/or iso-C(17∶1)I). 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)).