Allen G. Marr

THE MAINTENANCE REQUIREMENT OF ESCHERICHIA COLI

Not all of the reactions that consume the carbon and energy source are directly coupled with growth. Motility requires an expenditure of adenosine triphosphate ( ATP) ( Sherris et nl., 1957). The accumulation of solutes to a higher concentration in the cell than in the medium requires an initial expenditure of energy (Kepes, 1960; Patlak, 1961 ). If the cell is permeable to the solute, the cell must expend metabolic energy continuously to maintain a higher intracellular than extracellular concentration. Finally, the hydrolysis of proteins and nucleic acid to their constituent monomers and resynthesis of the macromolecules from those monomers undoubtedly consumes ATP. McGrew and Mallette (1962) have reviewed the opinions of microbiologists concerning the need for metabolic energy to meet the demand of chemical and physical wear and tear and have defined the energy required to maintain the status quo as the energy of maintenance. For the purpose of this paper the definition of energy of maintenance proposed by McGrew and Mallette will be modified such that the definition coincides with an experimentally measurable quantity, the specific maintenance (see equation 2) . The specific maintenance represents the consumption of the source of carbon and energy for purposes that are not a function of the rate of growth. THEORY

Role of feedback inhibition in stabilizing the classical operon

Abstract The Goodwin equations for a repressible operon (Goodwin, 1965) are modified (1) to describe a time lag between genetic regulation and appearance of functional enzyme, (2) to describe consumption of endproduct in protein synthesis, and (3) to describe feedback inhibition of enzyme activity. The stability of the modified equations is determined by a method outlined in the appendix which treats a class of negative feedback systems with time delays. With parameters estimated from experimental data on the tryptophan operon of Escherichia coli, we conclude that the operon becomes unstable as normal feedback inhibition is lost. Numerical solution of the modified equations shows that an example with a partial loss of feedback inhibition can have a period of oscillation less than the cell generation time, and the numerical solutions are shown to be in qualitative agreement with experiments showing oscillations in tryptophan operon expression.

Hydroxy fatty acids of azotobacter agilis

Abstract Approximately half of the fatty acids recovered after alkaline hydrolysis of the bound lipid of Azotobacter agilis were hydroxy acids. The hydroxy acids were isolated by gas-liquid chromatography and were identified as 3-hydroxydecanoic, 3-hydroxydodecanoic and 2-hydroxydodecanoic acids by the retention volume of the methyl ester in gas-liquid chromatography, by infrared spectrum, and by identification of the products of oxidation by permanganate. The chain length of β-hydroxy fatty acids was confirmed by dehydration-hydrogenation, which gave the expected n -saturated acids.

Studies on the repression of β-galactosidase in Escherichia coli

The mechanism of catabolite repression has been tested in mutants of Escherichia coli and a mutant of Aerobacter aerogenes, JF-4, using the technique of nutrient limitation. Two distinct types of enzyme control have been identified: (1) a control which is antagonized by inducer and is called “inducer-specific repression”; and (2) a control which is independent of the concentration of inducer and is called “inducer-independent represseion”. A metho of analysis is employed which allows each of the two types of repression to be measured quantitavely. The restriction of catabolic activities leads to derepression while the restriction of anabolic activities leads to repression; however, the relative change in inducer-specific and inducer-independent repression are not the same. Carbon limitation leads to a preferential decrease in inducer-specific repression while nitrogen and sulfur limitation lead to a preferential increase in inducer-independent repression.

Kinetics of induction of mannitol dehydrogenase in Azotobacter agilis

Abstract Mannitol dehydrogenase is induced gratuitously by ribitol in Azotobacter agilis. In batch cultures the enzyme is synthesized at an increasing specific rate for several hours after addition of ribitol. Several possible explanations of the kinetics trivial to induced synthesis per se such as the requirement for synthesis of a specific transfort system were eliminated. The kinetics of induced synthesis of mannitol dehydrogenase in unrestricted and in sulfate-limited continuous cultures were comparable to the kinetics in batch culture; however, continuous cultures limited by the concentration of the carbon source formed mannitol dehydrogenase at a constant specific rate shortly after the addition of inducer.

Modification of the Beckman model DU spectrophotometer for recording linearly in absorbancy at fixed wavelength

Abstract The Beckman DU spectrophotometer has been adapted for recording with a commercial direct-current amplifier and a network of biased silicon diodes to generate the absorbancy function from 0 to 1. The network was designed to provide maximum accuracy between 0 and 0.5 absorbancy to permit the use of expanded scales. This adaptation is not only compatible with but improves the precision of photometric measurement manually by null balance.

A membrane filter direct count technique for enumeratingBdellovibrio

A membrane filter direct count method was devised for enumeratingBdellovibrio cells in “clean” suspensions. The procedure involves filtering a specified volume of a diluted, Trisbuffered suspension ofBdellovibrio cells through a known area of a 100-nm-pore-size Millipore brand membrane filter. A clarification solvent was used to render the filter transparent, so that the bdeloyvibrios on the filter could be photomicrographed and counted either visually or by means of a Quantimet 720 Image Analyzing Computer. The number ofBdellovibrio cells per milliliter in the undituted suspension could be calculated from the mean number of cells per unit area of the filter, the dilution factor, and the volume of diluted suspension filtered. TheBdellovibrio cells were distributed on the filters in a Poisson manner when there were not more than about 3.5 cells per 100 μm2 of filter surface. The membrane filter direct counts correlated well with direct counts obtained by the Petroff-Hausser method. The correlation of direct counts with plaque (“viable”) counts showed that 80 to 95% of the direct-countedBdellovibrio cells in the clean suspensions were capable of forming plaques on lawns of suitable substrate bacteria. *** DIRECT SUPPORT *** A01R4002 00007