by aldehyde dehydrogenase and the response regulator AlgR. The cysts of Azotobacter are spherical and consist of the so-called "central body" – a reduced copy of vegetative cells with several vacuoles – and the "two-layer shell". The inner part of the shell is called intine and has a fibrous structure. The outer part has a hexagonal crystalline structure and is called exine. Exine is partially hydrolyzed by trypsin and is resistant to lysozyme, in contrast to the central body. The central body can be isolated in a viable state by some chelation agents. The main constituents of the outer shell are alkylresorcinols composed of long aliphatic chains and aromatic rings. Alkylresorcinols are also found in other bacteria, animals, and plants. Germination of cysts A cyst of the genus Azotobacter is the resting form of a vegetative cell; however, whereas usual vegetative cells are reproductive, the cyst of Azotobacter does not serve this purpose and is necessary for surviving adverse environmental factors. Following the resumption of optimal environmental conditions, which include a certain value of pH, temperature, and source of carbon, the cysts germinate, and the newly formed vegetative cells multiply by a simple division. During the germination, the cysts sustain damage and release a large vegetative cell. Microscopically, the first manifestation of spore germination is the gradual decrease in light refractive by cysts, which is detected with phase contrast microscopy. Germination of cysts takes about 4–6 h. During germination, the central body grows and captures the granules of volutin, which were located in the intima (the innermost layer). Then, the exine bursts and the vegetative cell is freed from the exine, which has a characteristic horseshoe shape. This process is accompanied by metabolic changes. Immediately after being supplied with a carbon source, the cysts begin to absorb oxygen and emit carbon dioxide; the rate of this process gradually increases and saturates after four hours. The synthesis of proteins and RNA occurs in parallel, but it intensifies only after five hours after the addition of the carbon source. The synthesis of DNA and nitrogen fixation are initiated 5 hours after the addition of glucose to a nitrogen-free nutrient medium. Germination of cysts is accompanied by changes in the intima, visible with an electron microscope. The intima consists of carbohydrates, lipids, and proteins and has almost the same volume as the central body. During germination of cysts, the intima hydrolyses and is