Characteristics of Azotobacter Azotobacter is a genus of bacteria that live in soil and have the following characteristics: They are bacilli. They are gram-negative. They are obligate aerobes. They can fix nitrogen. (Unlike some other nitrogen-fixing bacteria, which associate with the roots of plants, Azotobacter species are free-living.) Select the four statements that are true for bacteria in the genus Azotobacter. They are poisoned by O_2. They appear purple after Gram staining. They have a relatively thin layer of in their cell wall. They require amino acids or other organic molecules as a source of nitrogen. They use O_2 for cellular respiration. They can carry out anaerobic respiration in an environment that lacks O_2. They are shaped like rods. They have the appearance of coils or corkscrews. They can convert atmospheric nitrogen to ammonia.