Azotobacteraceae

The family Azotobacteraceae contains aerobic diazotrophs with two genera, Azomonas and Azotobacter, distinguished by the ability to form cysts. The family is also characterized by variable cell shape, the classic shape being ovoid, while many are pleomorphic. With an adequate supply of molybdenum, the Azotobacteraceae are able to fix at least 10 mg of molecular nitrogen per gram of carbohydrate consumed under aerobic conditions. Like most Pseudomonadaceae, the Azotobacteraceae are able to use a wide variety of carbon sources, including sucrose. Recent analysis of the unannotated genome of Azotobacter vinelandii has shown this bacterium is most appropriately grouped in the family Pseudomonadaceae. The original familial distinction was based on the ability to fix nitrogen, but a few Pseudomonadaceae have been found to fix nitrogen, as well. The relation is not surprising given the ability of many Azotobacteraceae to fluoresce due to the production of pyoverdine, a nonribosomal peptide siderophore typical of many Pseudomonadaceae.