Azotobacter vinelandii has been characterized by its lack of acid production in culture1. In fact, most species of Azotobacter do not form acid, but appear to oxidize carbohydrates completely to carbon dioxide and water2. The notable exceptions to this are the acid-tolerant A. indicum (Beijerinckia indica)3 and A. macrocytogenes4 that are characterized by acid production. Other acid-tolerant species are not reported to be acid producers. There have been a few scattered reports of acid production by A. vinelandii, but these usually mention that it occurred during abnormal cultural conditions5, or with little or no growth6.