Permeability of Staphylococcus aureus to the Sideromycin antibiotic A 22,765

Mechanisms of resistance in Escherichia coli to the sideromycin antibiotic no. 216: isolation and characterization of the resistant mutants

Escherichia coli easily developed resistance to a new antimicrobial agent of the sideromycin group, No. 216, by spontaneous mutation. Most of the No. 216-resistant mutants tested proved not to be cross-resistant to E. coli phages T1, T5, and ø80. On the other hand, these phage-resistant mutants were cross resistant to No. 216. The initial site for binding of No. 216 to the sensitive cells was located, at the ton A gene product (Ton A-protein) of the outer membrane. However, unlike the phage-resistant mutants, ton A protein (78K-protein) in most No. 216-resistant mutants was intact and these mutants were possessed a particular 87K protein in the outer membrane. It is suggested that No. 216 is taken up by ton A protein and then penetrates into the cell by way of a particular transport system and that a highly mutable portion may exist in this reaction system.

[Membrane permeability and antibiotic resistance in bacteria]

The resistance of mainly gram-negative bacteria against antibiotics is discussed with respect to new discoveries on the permeability barrier of the outer membrane. Proteins originally characterized as virus receptors have been found to be involved in the translocation of certain substrates across the membrane. Antibiotics can reach their target by the same "pores".

Ferric hydroxamate transport without subsequent iron utilization in Bacillus megaterium

Iron transport and utilization were examined in Bacillus megaterium Ard1, a mutant that is resistant to the hydroxymate antibiotic A22765 and whose growth is inhibited by the structurally similar hydroxamate Desferal. Rapid, low-level uptake of Desferal-50Fe was observed; such uptake was temperature and energy independent. Gel filtration chromatography of the cytoplasmic fraction of protoplasts labeled with Desferal-55Fe for 30 to 120 s demonstrated only unchanged esferal-55Fe in the cytoplasm. Although B. megaterium Ard1 showed transport of Desferal-59Fe by a process that resembles facilitated diffusion, this organism was unable to transfer iron from this chelate to cellular macromolecules for metabolic use. High-level transport of the ferric hydroxamate schizokinen-59Fe by B. megaterium Ard1 was both temperature and energy dependent. Within 30 s, protoplasts labeled with schizokinen-55Fe contained iron associated with certain macromolecules and in an apparent "pool" of schizokinen-55Fe in the cytoplasmic fraction. Prior transport of Dseferal-55Fe by protoplasts of strain Ard1 did not interfere with subsequent transport and utilization of schizokinen-59Fe. These studies suggest that transport of ferric hydroxamates may occur by a facilitated diffusion-type process; transfer of iron to cellular macromolecules may drive high-level transport of the chelate and may be the step at which energy is required in the iron transport-assimilation process.

Hydroxamate recognition during iron transport from hydroxamate-ion chelates

Kinetics of radioactive iron transport from three structurally different secondary hydroxamate-iron chelates (schizokinen-iron, produced by Bacillus megaterium ATCC 19213; Desferal-iron, produced by an actinomycete; and aerobactin-iron, produced by Aerobacter aerogenes 62-1) revealed that B. megaterium SK11 (a mutant which cannot synthesize schizokinen) has a specific transport system for utilization of ferric hydroxamates with a recognition capacity based on the chemical structure of the hydroxamate. Both Desferal and schizokinen enhanced iron uptake in this organism; however, Desferal-iron delivered only one-sixth the level of iron incorporated from the schizokinen-iron chelate. Desferal-iron did not generate the rapid rates of iron transport noted with schizokinen-iron at elevated iron concentrations. Assays containing large excesses of either iron-free Desferal or iron-free schizokinen suggested that the iron-free hydroxamate may compete with the ferric hydroxamate for acceptance by the transport system although the system has greater affinity for the iron chelate. Aerobactin-iron did not stimulate iron uptake in B. megaterium SK11 and aerobactin inhibited growth of this organism, indicating that B. megaterium SK11 cannot efficiently process the aerobactin-iron chelate.

Fate of labeled hydroxamates during iron transport from hydroxamate-ion chelates

The fate of the hydroxamic acid-iron transport cofactors during iron uptake from the (59)Fe(3+) chelates of the (3)H-labeled hydroxamates schizokinen and aerobactin was studied by assay of simultaneous incorporation of both (59)Fe(3+) and (3)H. In the schizokinen-producing organism Bacillus megaterium ATCC 19213 transport of (59)Fe(3+) from the (3)H-schizokinen-(59)Fe(3+) chelate at 37 C was accompanied by rapid uptake and release (within 2 min) of (3)H-schizokinen, although (3)H-schizokinen discharge was temperature-dependent and did not occur at 0 C. In the schizokinen-requiring strain B. megaterium SK11 similar release of (3)H-schizokinen occurred only at elevated concentrations of the double-labeled chelate; at lower chelate concentrations, (3)H-schizokinen remained cell-associated. Temperature-dependent uptake of deferri (iron-free) (3)H-schizokinen to levels equivalent to those incorporated from the chelate form was noted in strain SK11, but strain ATCC 19213 showed only temperature-independent binding of low concentrations of deferri (3)H-schizokinen. These results indicate an initial temperature-independent binding of the ferric hydroxamate which is followed rapidly by temperature-dependent transport of the chelate into the cell and an enzyme catalyzed separation of iron from the chelate. The resulting deferri hydroxamate is discharged from the cell only when a characteristic intracellular concentration of the hydroxamate is exceeded, which happens in the schizokinen-requiring strain only at elevated concentrations of the chelate. This strain also appears to draw the deferri hydroxamate into the cell by a temperature-dependent mechanism. The aerobactin-producing organism Aerobacter aerogenes 62-1 also demonstrated rapid initial uptake and temperature-dependent discharge of (3)H-aerobactin during iron transport from (3)H-aerobactin-(59)Fe(3+), suggesting a similar ferric hydroxamate transport system in this organism.

Iron uptake in Salmonella typhimurium: utilization of exogenous siderochromes as iron carriers

Aerobic microorganisms have evolved a variety of siderochromes, special ligands which can dissolve insoluble ferric iron and facilitate its transport into the cell. We have found that enb mutants of Salmonella typhimurium blocked in the biosynthesis of enterobactin (its natural iron carrier) are able to utilize siderochromes of different types made by other microorganisms as iron carriers. The antibiotic albomycin delta(2) was used to select mutants defective in ferrichrome-mediated iron uptake. Twelve classes of albomycin-resistant mutants, named sid, were defined on the basis of their growth responses to other siderochromes. Most of these classes have genetic lesions in loci that are cotransduced with panC (represented at 9 min on the genetic map). The locus designated sidJ is cotransduced with enb, whereas sidK and sidL are linked with neither panC nor enb. Genetic and physiological data indicate that S. typhimurium has several transport systems of high specificity for a variety of siderochromes produced by other microorganisms.

Active transport of iron in Bacillus megaterium: role of secondary hydroxamic acids

Kinetics of radioactive iron transport were examined in three strains of Bacillus megaterium. In strain ATCC 19213, which secretes the ferric-chelating secondary hydroxamic acid schizokinen, (59)Fe(3+) uptake from (59)FeCl(3) or the ferric hydroxamate Desferal-(59)Fe(3+) was rapid and reached saturation within 3 min. In strain SK11, which does not secrete schizokinen, transport from (59)FeCl(3) was markedly reduced; the two ferric hydroxamates Desferal-(59)Fe(3+) or schizokinen-(59)Fe(3+) increased both total (59)Fe(3+) uptake and the (59)Fe(3+) appearing in a cellular trichloroacetic acid-insoluble fraction, although 10 min was required to reach saturation. Certain characteristics of transport from both ferric hydroxamates and FeCl(3) suggest that iron uptake was an active process. The growth-inhibitory effect of aluminum on strain SK11 was probably due to the formation of nonutilizable iron-aluminum complexes which blocked uptake from (59)FeCl(3). Desferal or schizokinen prevented this blockage. A strain (ARD-1) resistant to the ferric hydroxamate antibiotic A22765 was isolated from strain SK11. Strain ARD-1 failed to grow with Desferal-Fe(3+) as an iron source, and it was unable to incorporate (59)Fe(3+) from this source. Growth and iron uptake in strain ARD-1 were similar to strain SK11 with schizokinen-Fe(3+) or the iron salt as sources. It is suggested that the ferric hydroxamates, or the iron they chelate, may be transported by a special system which might be selective for certain ferric hydroxamates. Strain ARD-1 may be unable to recognize both the antibiotic A22765 and the structurally similar chelate Desferal-Fe(3+), while retaining its capacity to utilize schizokinen-Fe(3+).

Rhodotorulic acid from species of Leucosporidium, Rhodosporidium, Rhodotorula, Sporidiobolus, and Sporobolomyces, and a new alanine-containing ferrichrome from Cryptococcus melibiosum

An examination of 142 strains within 19 genera of yeasts and yeastlike organisms for formation of hydroxamic acids in low-iron culture showed production of hydroxamates by two unclassified strains and by 52 strains among the genera Aessosporon (3 of 3 strains), Cryptococcus (1 of 43), Leucosporidium (3 of 11), Rhodosporidium (4 of 4), Rhodotorula (27 of 39), Sporidiobolus (2 of 2), and Sporobolomyces (12 of 13). Crystalline rhodotorulic acid was isolated in amounts sufficient to account for most or all of the measured hydroxamate in culture supernatants of 16 strains representative of the five last-mentioned hydroxamate-producing genera. A new alanine-containing ferrichrome was isolated from one strain of Cryptococcus melibiosum. Rhodotorulic acid was a major metabolic product of many of the positive strains when grown in low-iron media, and iron was shown to repress its synthesis and excretion into the culture medium. The taxonomic significance of production of hydroxamic acids is described in connection with the position of these yeast species in the subclass Heterobasidiomycetidae.