SUMMARYA simple chemically defined medium for examining the motility of Escherichia coli K 12 was designed. The essential components were: (1) a chelating agent to protect the motility against inhibition by traces of heavy metal ions; (2) a buffer to keep the pH value at the optimum between pH 6.0 and 7-5; (3) an energy source to stimulate the motility above that allowed by an endogenous energy source. Oxygen was required unless an energy source was provided which yielded energy anaerobically. A temperature optimum was determined.A chemically defined growth medium capable of producing motile bacteria was devised. It was found that the presence of glucose or growth above 37" prevented synthesis of flagella. I N T R O D U C T I O NFor many studies of bacterial motility, it would be desirable to work with chemically defined media and to know the effect of commonly encountered variables. The present work aimed to meet the following objectives. (a) To design for studying motility a medium which contained only known chemicals and which did not allow growth. (b) To determine the optimal conditions for motility in this medium, including the effects of pH value, temperature, ionic strength and the concentration of oxygen. (c) To find a chemically defined growth medium and suitable growth conditions for producing motile bacteria.Escherichia coli was chosen because the vast knowledge of its biochemistry and genetics should be applicable to the study of numerous problems of bacterial motility. Many strains of E. coli are motile by virtue of having several flagella distributed around the cell.To make the necessary measurements of motility, an assay described in the preceding paper by Adler & Dahl(l967) was used. By omitting methionine from the medium, it was possible to study motility in the absence of chemotaxis. METHODSThe strain ~2 7 5of Escherichia coli was the same as that described by Adler & Dahl (1967) ; this strain is F-, threonine-, leucine-, methionine-, lactose-, phosphatase-, lysogenic for A, resistant to h and T 1 , streptomycin-resistant and motile. The bacteria
This study compares the effects of a structured exercise training program to the therapeutic benefits of a ‘support’ group on the depressed mood and reduced performance of pleasant activities by hemodialysis patients. After 6 months of an aerobic exercise training program, the 10 exercisers showed a significant increase in maximal aerobic capacity (VO2max) and a significant decrease in dysphoric mood when compared to 7 patients attending the support group. Support group participants reported a significant decrease in pleasant activities while there was no change in the exercisers. Eighteen months after the exercise training program, the exercisers reported continued low levels of depressed mood, and were performing significantly more pleasant activities than they reported prior to the exercise program. The results of this study suggest an exercise training program may be useful in the psychosocial rehabilitation of some hemodialysis patients.
Although amino acid transport has been extensively studied in bacteria during the past decade, little is known concerning the transport of those amino acids that are biosynthetic intermediates or have multiple fates within the cell. We have studied homoserine and threonine as examples of this phenomenon. Homoserine is transported by a single system which it shares with alanine, cysteine, isoleucine, leucine, phenylalanine, threonine, tyrosine, and valine. The evidence for this being the sole system for homoserine transport is (i) a linear double-reciprocal plot showing a homoserine Km of 9.6 x 10-6 M, (ii) simultaneous reduction by 85% of homoserine and branched-chain amino acid uptake in a mutant selected for its inability to transport homoserine, and (iii) simultaneous reduction by 94% of the uptake of homoserine and the branched-chain amino acids by cells grown in millimolar leucine. Threonine, in addition to sharing the above system with homoserine, is transported by a second system shared with serine. The evidence for this second system consists of (i) incomplete inhibition of threonine uptake by any single amino acid, (ii) only 70% loss of threonine uptake in the mutant unable to transport homoserine, and (iii) only 40% reduction of threonine uptake when cells are grown in millimolar leucine. In this last case, the remaining threonine uptake can only be inhibited by serine and the inhibition is complete.
Homoserine is transported by a single system that it shares with alanine, isoleucine, leucine, phenylalanine, threonine, valine and perhaps cysteine, methionine, serine, and tyrosine. We investigated the regulation of this transport system and found that alanine, isoleucine, leucine, methionine, and valine each repress the homoserine-transporting system. From the concentration resulting in 50% repression of this transport system and the maximal amount of repression, we ranked the amino acids according to their effectiveness in repressing homoserine transport (in decreasing order): leucine>methionine>alanine>valine>isoleucine. The exponential rate of decrease in transport capacity after leucine addition equals the exponential growth rate of the culture, and protein synthesis is necessary for the derepression seen when leucine is removed. Threonine, in addition to using the above system, is transported by a second system shared with serine. We present further evidence for this serine-threonine transport system and show that it is not regulated like the homoserine-transporting system.
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