Azotobacter vinelandii exhibited diauxie when grown in a medium containing both acetate and glucose as carbon sources. Acetate was used as the primary carbon source during the acetate-glucose diauxie. Uptake of acetate was constitutively expressed during both diauxic phases of growth. Induction of the glucose uptake system was inhibited in the presence of acetate. Acetate was also the preferred growth substrate for A. vinelandii grown in a medium containing either fructose, maltose, xylitol, or mannitol. The tricarboxylic acid cycle intermediates citrate, isocitrate, and 2-oxoglutarate inhibited glucose utilization in cells grown in glucose medium containing these substrates, and diauxic growth was observed under these growth conditions. Temporal expression of isocitrate-lyase, ATPase, and nitrogenase was exhibited during acetate-glucose diauxie. Diauxic growth is observed when an organism is grown in a medium containing two carbon sources, and there is a preferential utilization of one carbon source before the metabolism of the other. A biphasic growth curve results. A classical example is observed when Escherichia coli is grown in a medium containing both glucose and lactose as carbon sources. Under this condition glucose is metabolized preferentially; after it is depleted from the medium, lactose catabolism commences. The inability of cells to ferment lactose in the presence of glucose has been attributed to the inhibitory effects of glucose or its metabolic products on the synthesis and activity of certain enzymes involved in lactose utilization. Catabolite repression or catabolite repression-like phenomena have been described in bacteria other than E. coli. Recently such a phenomenon has been reported for Rhizobium meliloti, a symbiotic nitrogen-fixing bacterium. Diauxic growth is observed when this organism is grown on succinate and lactose (17). The addition of cyclic AMP to this system does not cause reversal of the diauxie. Diauxie has also been described in Propionibacterium shermanii when it is grown anaerobically in glucose-lactate medium (12). The yeast Candida tropicalis exhibits glucose repression of cellobiose utilization, also producing diauxie (1). Dijkhuizen et al. (8) have described a diauxie phenomenon for Pseudomonas oxalaticus growing on mixtures of oxaloacetate and fumarate or acetate. Oxaloacetate transport is not inhibited by fumarate or acetate, suggesting that the pathway intermediate oxalyl coenzyme A may be the target for formate and acetate inhibition. We report here diauxic growth which occurs when Azotobacter vinelandii, a nonsymbiotic nitrogen-fixing bacterium, is grown on medium containing both acetate and glucose. The effects of acetate on the glucose uptake system as well as other carbohydrates in A. vinelandii are reported. These studies reveal some aspects of possible regulatory processes in A. vinelandii not yet studied with regard to substrate uptake and biological nitrogen fixation. MATERIALS AND METHODS Chemicals and enzymes. The following chemicals used in this study we...

Short Flexibacter FS-1 cells, generated during logarithmic growth in glucosesalts medium or by filament fragmentation during the transition from log to stationary phase in rich medium, are unable to glide. Motility returns when cells elongate. This strain also dissociates stable, short, nongliding variants.