A Mutant of Escherichia coli with a Defect in Energy Metabolism

Abstract

A mutant of Escherichia coli with a decreased growth efficiency has been investigated. The results of growth studies with different substrates and of measurement of P/O ratios in membrane preparations suggest that the strain is defective in the ability to couple synthesis of ATP to electron transport. I N T R O D U C T I O NEscherichia coli strain 15-28 is a mutant containing an abnormally high concentration of the immediate precursor to the 50 s ribosomal subunit (MacDonald, Turnock & Forchhammer, 1967). The strain grows much less quickly than the wild-type and a genetic analysis (Turnock, 1969) showed that at least two mutations are responsible for its complex phenotype. One of these mutations (b-; Turnock, 1969) confers upon the cell an altered response to the antibiotic streptomycin and a decreased efficiency in the utilization of the growth substrate, compared to the parent strain. The latter property is examined in this paper; the results obtained suggest that the mutation reduces the efficiency of energy metabolism, probably that associated with oxidative phosphorylation. The significance of this finding and ways in which other mutants defective in oxidative phosphorylation might be selected are discussed. METHODSStrains of Escherichia coli. The two strains, b-and b f , used in tlus paper were obtained by mating Hfr 15-5 with strain 1 5 -2 8~ (Turnock, 1969). They both carry the same str and thy alleles, but do not contain the mutation responsible for the high concentration of ribosome precursor in strain 15-28.Media and growth conditions. Unless otherwise stated, liquid cultures were grown with aeration by shaking at 37'. Culture population densities were measured spectrophotometrically at 450 nm with a Gilford microsample spectrophotometer (light path, I cm). The minimal salts medium used was that of Turnock (1969), supplemented with thymine (10 mg/l) and glucose (2 g/l) or carbon source as indicated. For the preparation of cell-free extracts the bacteria were grown in minimal medium with glucose as carbon source supplemented with I % vitamin-free Casamino acids.For growth under anaerobic conditions, inocula were grown in screw-capped bottles filled to the neck with medium and diluted into growth flasks bubbled with95 % N2, 5% CO,. When NO3-(as 0-1 % KNO,) was used as the terminal electron acceptor, the flasks were bubbled with N,, and NaHCO, (25 mM) included in the medium (Cox et al. 1970).Growth yields. The extinction of the culture, measured at 450 nm, is proportional to the cell mass (Schaechter, Maalere & Kjeldgaard, 1958) and so this parameter was employed to

Effects of Membrane-Energy Mutations and Cations on Streptomycin and Gentamicin Accumulation by Bacteria: a Model for Entry of Streptomycin and Gentamicin in Susceptible and Resistant Bacteria

“…Alternatively, internalization of the aminoglycoside when bound to a ribosomal site could enhance the protonmotive force due to the electrochemical characteristics of aminoglycosides. An increased rate of streptomycin and gentamicin entry has been shown here to occur with AN120 and apparently in a mutant described by Turnock et al (38,39), so this seems a feasible proposal. Mutants 12,1977 on May 12, 2018 by guest http://aac.asm.org/ (F. L. Jackson, unpublished data) (uncoupled bacteria utilize succinate poorly as an energy source), and loss of permeability control for amino acids and nucleotides (1,18).…”

Active transport in mutants of Escherichia coli with alterations in the membrane ATPase complex

“…A number of mutants ofEscherichia coli have been isolated with a defect in oxidative phosphorylation [1][2][3][4][5][6][7]. The mutants isolated thus far, all map in the same region of the chromosome (73.5 min) and all are affected in the membrane Mg 2÷-Ca 2+ ATPase complex.…”

“…The mutants isolated thus far, all map in the same region of the chromosome (73.5 min) and all are affected in the membrane Mg 2÷-Ca 2+ ATPase complex. One class of mutants has been shown to lack ATPase catalytic activity [1,3,5,7], while a second class of mutants retains the ATPase activity [2,4,6], but in a form which is resistant to the energy transfer inhibitor DCCD** [2]. Studies of active transport in mutants of the first class have provided evidence that phosphate-bond energy is not required for the aerobic transport of certain solutes in E. coli [5,8,9].…”

Purification and Properties of Reconstitutively Active and Inactive Adenosinetriphosphatase from Escherichia coli

“…Mutants lacking this enzyme were isolated in several laboratories (1)(2)(3)(4)(5)(6)(7). Studies with such mutants have been useful in distinguishing transport systems driven by an energized membrane state from those that require substrate level phosphorylation (8,9).…”