Chlorotetracycline as a fluorescent probe for membrane events in the action of colicin K on Escherichia coli

Membrane deenergization by colicin K affects fluorescence of exogenously added but not biosynthetically esterified parinaric acid probes in Escherichia coli

Fluorescence of the conjugated polyene fatty acid, parinaric acid (PnA), was studied in membranes of Escherichia coli during deenergization by colicin K. The free fatty acid and biosynthetically esterified forms of cis-PnA (9,11,13,15-cis,trans,trans,cis-octadecatetraenoic acid), both of which are sensitive to E. coli lipid-phase transitions, were compared. When free cis-PnA was added exogenously to respiring bacteria, dissipation of the energized state of the membrane resulted in a dramatic increase in cis-PnA fluorescence; all-trans-PnA was much less sensitive. Neither spectral shifts nor a change in cis-PnA fluorescence polarization were observed. Analysis of the PnA content of extracellular fractions of deenergized and control cells revealed a difference in probe distribution: the membranes of energy-poisoned E. coli bound about 77% of exogenously added cis-PnA, whereas membranes of actively respiring controls bound only about 44%. No fluorescence enhancement was observed in cells centrifuged to remove unbound cis-PnA before colicin treatment. When cis-PnA was biosynthetically esterified to phospholipids of an unsaturated fatty acid auxotroph of E. coli, the fluorescence did not change during membrane deenergization. In double-probe experiments, membrane deenergization resulted in fluorescence enhancement of exogenously added N-phenyl-1-naphthylamine, without change in esterified PnA fluorescence. We conclude that deenergization of E. coli membranes leads to increased binding and fluorescence of exogenously added PnA and cannot be detected from within the inner and outer membranes by PnA esterified in vivo.

Relationship between steps in 8-anilino-1-naphthalene sulfonate (ANS) fluorescence and changes in the energized membrane state and in intracellular and extracellular adenosine 5'-triphosphate (ATP) levels following bacteriophage T5 infection of Escherichia coli

The addition of bacteriophage T5 to anaerobic, fermenting cells of Escherichia coli B or K-12 in the presence of 8-anilino-1-naphthalene sulfonate (ANS), N-phenylnaphthyl-1-amine (NPN), or dansyl ethylamine causes the fluorescence of these probes to rise in two steps, the first occurring immediately upon addition, the second delayed by 6 min. The conditions necessary for observing this phenomenon are defined (cell density, probe concentration, substrate, absence of an electron acceptor, multiplicity of infection, growth, and harvesting conditions). The magnitudes of the first and second steps in fluorescence are dependent upon the multiplicity of infection; the timing of the steps is not. The first step correlates with a breakdown in the potassium or rubidium permeability barrier of the cells, and it occurs either aerobically or anaerobically, with fermentable or nonfermentable substrates. The second step occurs only with cells that are without an available electron acceptor, are fermenting, and which have a functional membrane-bound, Ca2+-dependent adenosine triphosphatase (ATPase). The results are consistent with disturbance of energization of the cell membrane by the membrane-bound ATPase at the time of the second step in fluorescence. No changes in the intracellular level of adenosine 5'-triphosphate (ATP) was seen, whereas the extracellular level increased sharply, starting 3--6 min after phage addition. The quantity of ATP found in the medium by 30 min after infection amounted to about four times the amount present inside the cells at the time of infection. The quantity and rate of efflux of ATP was similar under aerobic and anaerobic conditions.

Colicin K acts by forming voltage-dependent channels in phospholipid bilayer membranes

The bactericidal action of colicins K, E1, Ia, and other functionally related colicins involves disruption of active transport and leakage of ions from the cell. We show that a single colicin K molecule can form a voltage-dependent, relatively nonselective, ion-permeable channel of a few picosiemens conductance in a planar phospholipid bilayer membrane. In a membrane containing many of these channels, the ratio of the number of conducting to nonconducting channels changes e-fold per 3.7 mV. We suggest that the physiological effects of colicin K and functionally related colicins result from their ability to form ion-permeable channels in the bacterial plasma membrane.

Changes in fluorescence of 8-anilino-1-naphthalene sulfonate after bacteriophage T5 infection of Escherichia coli. Initial fluorescence rise coincides with onset of rubidium efflux

Escherichia coli cells pre-loaded with 86Rb+ begin to lose 86Rb+ immediately after phage T5 addition. The loss proceeds with negative-exponential (first-order) kinetics for up to approximately 15 min after phage addition. The constant which characterizes the rate of loss increases with increasing numbers of infecting phage per cell. It is known that anaerobic, fermenting cells of E. coli show a two-step increase in 8-anilino-1-naphthalene sulfonate (ANS) fluorescence upon infection with bacteriophage T5; the first rise begins immediately upon phage addition, the second 6 min later. The onset of 86Rb+ release, therefore, is correlated with the first fluorescence rise with respect to timing and response to the multiplicity of infection.

Formation of sugar phosphates in colicin K-treated Escherichia coli

Colicin K greatly decreased the incorporation of 32P-labeled inorganic orthophosphate into nucleotides and nucleic acids, causing a concomitant increase in the formation of 32P-labeled sugar phosphates in sensitive cells of Escherichia coli. These sugar phosphates were formed in aerobically growing cells, as well as in cells under stringent control of ribonucleic acid synthesis. The main 32P-labeled product was identified as sedoheptulose 7-phosphate in two strains (B1 and K-12 MK-1) and fructose 1,6-diphosphate in one strain (K-12 CP78). The formation of sugar phosphates induced by colicin K was inhibited by carbonyl cyanide m-chlorophenylhydrazone. It was also not observed in N,N'-dicyclohexylcarbodiimide-treated cells or Mg2+-(Ca2+)-adenosine triphosphatase-less mutant (strain K-12 AN120) cells. Thus, the formation of sugar phosphates in colicin K-treated cells is dependent on the formation of adenosine 5'-triphosphate by oxidative phosphorylation.

The state of energization of the membrane of Escherichia coli as affected by physiological conditions and colicin K

The bacterial protein colicin K, when added to sensitive Escherichia coli in the presence of 3,3'-dihexyloxacarbocyanine, cuases a doubling in fluorescence of the probe. Glucose and oxygen cause a decreased fluorescence while anoxia and cyanide cause a rise in fluorescence. These results in conjunction with the work of other laboratories suggest that colicin K causes a depolarization of the transmembrane electrical potential. Fluorescence in the absence of colicin K was relatively independent of KCl, NaCl, and MgCl2 concentrations below 0.1 M. Although colicin K caused rapid efflux of the K+ analogue 86Rb+, the fluorescence rise was only partially blocked by 0.13 M KCl. The level of fluorescence caused by the action of colcin K was inversely proportional to the logarithm of the concentration of MgCl2 over the range of 2 muM to 4 mM. This suggests that a Nernst electrochemical potential for an anion can counteract a membrane depolarization caused by colcin. After colcin K action, the fluorescence of the carbocyanine could be further increased by anoxia or cyanide. The distribution of the weak base dimethyloxazolidinedione indicated that the pH in the interior of aerobic E. coli supplied with lactate was alkaline by 0.1 unit and unaffected by colicin. These results suggest that colicin K does not completely depolarize the membrane potential and does not interfere with the component of membrane energization generated by electron transport. Colicin K does not act as a cationophore. The partial depolarization of the membrane may account for the inhibition of active solute transport caused by colicin K.

Sensitization of colicin K-treated bacteria by sodium dodecyl sulfate: presence of free colicin in colicin K-treated cultures of Escherichia coli

A method of assaying colicin K is described. It makes use of two properties of sodium dodecyl sulfate to protect bacteria against colicin action and to dissolve those bacteria on which colicin K had started its action. By this method, the kinetics of bacterial killing by colicin K have been measured directly in the treated culture without intervening dilution. The kinetics are exponential with time and are a function of the colicin multiplicity, as described previously, but do not reach a final plateau. At any time during colicin treatment, free colicin is found in the medium. Procedures that eliminate or destroy this free colicin, such as centrifugation and resuspension of the treated bacteria in a fresh medium, or addition of trypsin or sodium dodecyl sulfate to the treated culture stop bacterial killing.

Light-induced tetracycline accumulation by Rhodopseudomonas sphaeroides

Light has been used as a primary energy source in studies of tetracycline transport by Rhodopseudomonas sphaeroides. Accumulation of the antibiotic occurs in light, while efflux occurs in dark. Both fluorescence enhancement and radioisotopic tracing have been used to monitor transport. Km's obtained from both techniques are similar. Light-induced accumulation of tetracyclines is inhibited by a variety of inhibitors, including antimycin A, N-ethylmaleimide, carbonylcyanide m-chlorophenylhydrazone, and 2,4-dinitrophenol. A rapid efflux is observed after loading when cells are placed in the dark or treated with inhibitors.

Alterations in membrane function in an Escherichia coli mutant tolerant to colicins Ia and Ib

An Escherichia coli mutant (tolI) previously shown to be tolerant to colicins Ia and Ib is defective in several functions of the bacterial cytoplasmic membrane. When compared with its parental strain, X36, whole cells of tolI show reduced rates of respiration with succinate, malate, or lactate as the substrate but near-normal rates with glucose or glycerol. Cell membrane preparations prepared from tolI cells exhibit reduced succinate and D-lactate oxidase activity but elevated levels of reduced-form nicotinamide adenine dinucleotide (NADH) oxidase. tolI cells have reduced levels of succinate and D-lactate dehydrogenase but normal levels of NADH dehydrogenase. Glycerol-grown tolI cells and membrane vesicles prepared from such cells are defective in the active transport of several amino acids and thiomethyl-beta-D-galactoside; however, they accumulate higher levels of alpha-methylglucoside when compared with X36 whole cells or vesicles. Although tolI cells adsorb less colicin Ia at high colicin concentrations than do X36 cells, it is shown that the adsorption of an Ia molecule to tolI cells has a lower probability of eliciting cell death than does Ia adsorption to strain X36 cells. It is concluded that a single mutation can lead to an alteration in several aspects of cytoplasmic membrane function and colicin I sensitivity.

Energy requirement for the initiation of colicin action in Escherichia coli

1. Starved cells of a strain of Escherichia coli and its mutant uncA, treated with colicin K, E2 or E3, remained fully rescuable upon trypsin treatment (stage I in colicin action). The transition to stage II in colicin action (cells no longer rescuable by trypsin) was promoted by the addition of either glucose or D-lactate. 2. Aerobically glucose-grown cells of the normal strain were irreversibly killed by colicin K, E2 or E3 under anerobic conditions, while similarly treated cells ot its mutant uncA remained fully rescuable. The stage I-stage II transition in colicin action was blocked in normal cells under anaerobic conditions when succinate was the sole carbon source. 3. Arsenate alone had little effect on the progression of the stage I-stage II transition in normal cells, treated with colicin K. However, this transition was abolished in the presence of both arsenate and anaerobic conditions. 4. The initiation of colicin action could be coupled to the anaerobic electron transfer systems formate dehydrogenase-nitrate reductase and alpha-glycerophosphate dehydrogenase-fumarate reductase. 5. These results indicate that an energized state of the cytoplasmic membrane is required for the initiation of colicin action and that no high-energy phosphorylated compounds are necessary.