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Patterns of chemotaxis by Salmonella typhimurium strain LT-2 to L-amino acids and to several sugars were quantitated by the Adler capillary procedure. Competition experiments indicated that LT-2 possesses three predominant receptors, or interacting sets of receptors, for amino acids. These were termed the aspartate, serine, and alanine classes, respectively. Studies with strains carrying point and deletion mutations affecting components of the phosphoenolpyruvate: glycose phosphotransferase system (PTS) made unlikely a role in primary reception of D-glucose by the three soluble PTS components, namely HPr, enzyme I, and factor III. A ptsG mutant defective in membrane-bound enzyme IB' of the high-affinity glucose transport system was shown to exhibit normal chemotaxis providing pleiotropic effects of the mutation were eliminated by its genotypic combination with other pts mutations or, phenotypically, by addition of cyclic AMP and substrate. A correlation was demonstrated between chemotaxis to glucose and activity of the low-affinity glucose transport complex, membranebound enzymes IIB:IIA, and an enzyme IIB:IIA mutant was shown to have a preponderant defect in chemotaxis to glucose and mannose. Of four systems capable of galactose transport, only the ,B-methylgalactoside transport system was implicated in chemotaxis to galactose. Some properties of a mutant possibly defective in processing of signals for chemotaxis to sugars is described. The Adler capillary assay (1, 2) has made it possible to measure semiquantitatively the chemotaxis responses of Escherichia coli (cf. 1, 4, 22), Bacillus subtilis (12, 31), and a Streptococcus (32) to a variety of compounds. Here we summarize some observations on the chemotaxis ofSalmonella typhimurium to some amino acids and sugars. We diagnose three primary receptors or receptor sets for amino acid chemotaxis in S. typhimurium. In concordance with studies of E. coli (1, 15, 23, 24), our physiological experiments and studies on an mgl (8-methylgalactoside [MGL] permease) and a galP melB (galactose permease, methyl-p-D-thiogalactoside [TMG] permease) double mutant have specifically implicated components of the MGL transport system in chemotaxis of S. typhimurium to galactose. Studies utilizing a series of mutants (8-10, t Contribution no.

Selection for resistance to the antibiotic fosfomycin (FOS; L-cis1,2-epoxypropylphosphonic acid, a structural analogue of phosphoenolpyruvate) was used to isolate mutants carrying internal and extended deletions of varying lengths within the ptsHI operon of Salmonella typhimurium. Strains carrying "tight" ptsI point mutations and all mutants in which some or all of the ptsI gene was deleted were FOS resistant. In contrast, strains carrying ptsH point mutations were sensitive to FOS. Resistance to FOS appeared to result indirectly from catabolite repression of an FOS transport system, probably the sn-glycerol-3phosphate transport system. Resistant ptsI mutants became sensitive to FOS when grown on i-glucose-6-phosphate, which induces an alternate transport system for FOS, or when grown in the presence of cyclic adenosine 3',5'monophosphate. A detailed fine-structure map of the pts gene region is presented. 785 on August 4, 2020 by guest

A.zo.to.bac' ter . Fr. n. azote nitrogen; M.L. masc. n. bacter the equivalent of Gr. neut. n. bactrum a rod or staff; M.L. masc. n. Azotobacter a nitrogen rod. Proteobacteria / Gammaproteobacteria / Pseudomonadales / Pseudomonadaceae / Azotobacter Cells range from straight rods with rounded ends to more ellipsoidal or coccoid , depending on the culture medium and age. Cells are up to 2 μm or more in diameter and 4 μm in length . A. paspali cells are usually longer, 5–10 µm in length, and can be filamentous, up to 60 µm long. Cells are usually single but may occur in pairs, irregular clumps (especially with A. paspali ), or, more rarely, in chains of varying length. Encystment occurs during late stationary phase at low frequency or at high frequency after culturing on butanol. Motile with peritrichous flagella or nonmotile. Aerobic, having a strictly respiratory type of metabolism with oxygen as the terminal electron acceptor. Nitrogen is fixed under microaerobic conditions (2% oxygen), under full aerobiosis, or after adaptation in hyperbaric oxygen. N 2 fixation uses Mo‐, V‐, or Fe‐containing nitrogenase enzymes, depending on the environmental metal supply. Water‐soluble and water‐insoluble pigments are produced by some strains of all species . Growth is heterotrophic; sugars, alcohols, and salts of organic acids are used as carbon sources. Ammonium salts, nitrate, and urea are used as sources of fixed nitrogen. Very few amino acids are used, probably due to a general deficiency in amino acid transport. The minimum pH for growth in the presence of fixed nitrogen sources ranges from 4.8 to 6.0 with maximum pH 8.5. The optimum pH for diazotrophic growth is 7.0–7.5. Most isolates are from soil, but a few are from water . One species ( A. paspali ) has been isolated only from roots of the tropical grass Paspalum notatum . The mol % G + C of the DNA is : 63.2–67.5. Type species : Azotobacter chroococcum Beijerinck 1901, 567.

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...