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In the present study, we demonstrate that the yeast form of Blastomyces dermatitidis can proliferate for short periods of time in the absence of ferric iron but not in the absence of calcium or magnesium. The results of this study shed light on the resistance of B. dermatitidis to chelating agents, such as deferoxamine, and may explain how B. dermatitidis resists the iron-binding activity of serum transferrin.

Recent studies have shown that Bordetella bronchiseptica utilizes a siderophore-mediated transport system for acquisition of iron from the host iron-binding proteins lactoferrin and transferrin. We recently identified the B. bronchiseptica siderophore as alcaligin, which is also produced by B. pertussis. Alcaligin production by B. bronchiseptica is repressed by exogenous iron, a phenotype of other microbes that produce siderophores. In this study, we report that alcaligin production by B. bronchiseptica RB50 and GP1SN was repressed by the Bordetella global virulence regulator, bvg, in addition to being Fe repressed. Modulation of bvg locus expression with 50 mM MgSO4 or inactivation of bvg by deletion allowed strain RB50 to produce alcaligin. In modulated organisms, siderophore production remained Fe repressed. These observations contrasted with our previous data indicating that alcaligin production by B. bronchiseptica MBORD846 and B. pertussis was repressed by Fe but bvg independent. Despite bvg repression of alcaligin production, strain RB50 was still able to acquire Fe from purified alcaligin, suggesting that expression of the bacterial alcaligin receptor was not repressed by bvg. We tested 114 B. bronchiseptica strains and found that bvg repression of alcaligin production was strongly associated with Bordetella phylogenetic lineage and with host species from which the organisms were isolated.

Both nickel-specific transport and nickel transport by a magnesium transporter have been described previously for a variety of nickel-utilizing bacteria. The derepression of hydrogenase activity in Bradyzhizobium japonicum JH and in a gene-directed mutant of strain JH (in an intracellular Ni metabolism locus), strain JHK7, was inhibited by MgSO4. For both strains, Ni2+ uptake was also markedly inhibited by Mg2+, and the Mg(2+)-mediated inhibition could be overcome by high levels of Ni2+ provided in the assay buffer. The results indicate that both B. japonicum strains transport Ni2+ via a high-affinity magnesium transport system. Dixon plots (1/V versus inhibitor) showed that the divalent cations Co2+, Mn2+, and Zn2+, like Mg2+, were competitive inhibitors of Ni2+ uptake. The KiS for nickel uptake inhibition by Mg2+, Co2+, Mn2+, and Zn2+ were 48, 22, 12, and 8 microM, respectively. Cu2+ strongly inhibited Ni2+ uptake, and molybdate inhibited it slightly. Respiratory inhibitors cyanide and azide, the uncoupler carbonyl cyanide m-chlorophenylhydrazone, the ATPase inhibitor N,N'-dicyclohexylcarbodiimide, and ionophores nigericin and valinomycin significantly inhibited short-term (5 min) Ni2+ uptake, showing that Ni2+ uptake in strain JH is energy dependent. Most of these conclusions are quite different from those reported previously for a different B. japonicum strain belonging to a different serogroup.

Magnesium sulfate is known to repress the expression of the virulence factors of Bordetella pertussis that are coordinately regulated by the bvg locus. We have tested the time required by MgSO4 to repress the synthesis of several bvg-regulated mRNA species and found that the promoters of the virulence genes (pertussis toxin, adenylate cyclase, and filamentous hemagglutinin) are repressed in 6 min, while the autogenously regulated promoters of the bvg locus (P1, P3, and P4) are repressed only several hours later. These data show a differential behavior between regulated and autoregulated genes of the bvg regulon.

In batch fermentations, optimal conversion of xylose to ethanol by recombinant Escherichia coli was obtained under the following conditions: 30 to 37 degrees C, pH 6.4 to 6.8, 0.1 to 0.2 M potassium phosphate buffer, and xylose concentrations of 8% or less. A yield of 39.2 g of ethanol per liter (4.9% ethanol by volume) was observed with 80 g of xylose per liter, equivalent to 96% of the maximum theoretical yield. Maximal volumetric productivity was 0.7 g of ethanol per liter per h in batch fermentations and 30 g of ethanol per liter per h in concentrated cell suspensions (analogous to cell recycling).

The uptake of circular and linear plasmid RSF0885 deoxyribonucleic acids, (DNAs) obtained from Haemophilus parainfluenzae 14, in both homologous and heterologous recipients was studied and compared with that of chromosomal DNA. High concentrations of divalent cations stimulated the uptake of either circular or linear plasmid DNA in H. parainfluenzae 14 competent cells but did not affect the uptake of chromosomal DNA. The biological activity of linear plasmid DNA was similar to that of circular DNA, and the transforming efficiencies for ampicillin resistance of both molecular forms were stimulated by divalent ions. Plasmid DNA was taken up efficiently either with or without the addition of divalent ions but was not biologically active in the heterologous Haemophilus influenzae Rd recipient. Our results suggest that in H. parainfluenzae 14 some of the steps for chromosomal and plasmid DNA uptake are different.

Cellular leakage observed in Escherichia coli K-12-M shortly after T7 infection might be the cause of arrested phage morphogenesis. We observed in this strain, but not in the normal host, a drastic reduction of the intracellular concentration of potassium (60%), magnesium (40%), putrescine (90%), and spermidine (40%), whereas ATP was not significantly reduced. Leakage started about 1 min after the addition of phage and was arrested 3 to 5 min postinfection. Larger molecules such as o-nitrophenyl-beta-D-galactopyranoside could not enter the cells, showing that the permeability of the membrane was not generally affected. To prevent their leakage, we increased the outside concentrations of several small molecules and ions. The yield of progeny phage was substantially increased by the addition of 100 mM MgSO4.

The effect of D-cycloserine on the establishment of twist states in Bacillus subtilis macrofibers was examined. Macrofibers produced in the presence of the drug differed in twist compared with those produced in its absence. The degree of twist alteration was dependent on the concentration of D-cycloserine in the growth medium. Macrofibers of different twist states representative of the entire twist spectrum from tight left-handedness to tight right-handedness were produced in strains FJ7 and C6D in four different ways: by control of the concentration of D-alanine, magnesium sulfate, or ammonium sulfate in the growth medium or by control of the growth temperature. The structures so produced were used to determine the effect of D-cycloserine on twist establishment starting from different twist states throughout the twist spectrum. In all but one case, twist resulting from growth in the presence of D-cycloserine was further towards the left-hand end of the twist spectrum than that produced in its absence, the exception being the unusual left-handed twist states produced in strains C6D and the closely related RHX 11S at high D-alanine concentrations described here. Studies of the interaction between D-cycloserine and D-alanine both used alone and used independently with the other twist-modifying systems (temperature, magnesium sulfate, and ammonium sulfate) revealed that changes in twist resulting from D-cycloserine were always in the opposite direction from those resulting from D-alanine. This antagonism suggests that the biochemical mechanism of twist regulation involves the metabolism of peptidoglycan, particularly reactions involving D-alanine or the dipeptide D-alanyl-D-alanine. This antagonism suggests that the biochemical mechanism of twist regulation involves the metabolism of peptidoglycan, particularly reactions involving D-alanine or the dipeptide D-alanyl-D-alanine. The possibility that peptidoglycan cross-linking is involved is discussed.

A selective medium containing 2 micrograms of dichloran per ml, 200 micrograms of chloramphenicol per ml, and 1.5% bacteriological peptone was developed for the isolation of Fusarium species and dematiaceous hyphomycetes from cereals. The medium, designated DCPA, was shown to select against species of Aspergillus, Penicillium, Cladosporium, and mucoraceous fungi. DCPA was evaluated for use as an enumeration medium and compared satisfactorily with dichloran-rose bengal-chloramphenicol agar when both media were tested with a range of cereal samples. Fusarium species and dematiaceous hyphomycetes produced well-formed colonies with good conidial production on DCPA, permitting rapid identification of such isolates on this medium.

Various methods of inducing autolysis of Escherichia coli cells were investigated, some being described here for the first time. For the autolysis of growing cells only induction methods interfering with the biosynthesis of peptidoglycan were taken into consideration, whereas with harvested cells autolysis was induced by rapid osmotic or EDTA shock treatments. The highest rates of autolysis were observed after induction by moenomycin, EDTA, or cephaloridine. The different autolyses examined shared certain common properties. In particular, regardless of the induction method used, more or less extensive peptidoglycan degradation was observed, and 10(-2) M Mg2+ efficiently inhibited the autolytic process. However, for other properties a distinction was made between methods used for growing cells and those used for harvested cells. Autolysis of growing cells required RNA, protein, and fatty acid synthesis. No such requirements were observed with shock-induced autolysis performed with harvested cells. Thus, the effects of Mg2+, rifampicin, chloramphenicol, and cerulenin clearly suggest that distinct factors are involved in the control of the autolytic system of E. Coli. Uncoupling agents such as sodium azide, 2,4-dinitrophenol, and carbonyl-cyanide-m-chlorophenyl hydrazone used at their usual inhibiting concentration had no effect on the cephaloridine or shock-induced autolysis.

The influence of osmolality on the effect of the novel beta-lactam antibiotic, mecillinam, on Escherichia coli was examined in a turbidimetric system. Both sucrose and sodium chloride were able to protect E. coli from the effects of mecillinam during the stage of conversion to morphologically abnormal forms, and the additional presence of small amounts of magnesium sulfate protected the spherical forms from subsequent lysis. More phenotypically "resistant" survivors were recovered in osmotically protective media than in broth of low osmolality. Sucrose appeared a better protective agent than sodium chloride, but growth of the phenotypically resistant population was much slower in the sucrose-containing than in sodium chloride-containing medium.

Human isolates of the intestinal pathogen Campylobacter jejuni have been shown to colonize mucus on the outer surface and deep within the intestinal crypts of gnotobiotic or germfree mice. The cecal crypts are preferentially colonized. A model of mucus colonization by C. jejuni in the mouse cecum has been developed, using antibiotic- and magnesium sulfate-treated specific-pathogen-free animals. These spiral-shaped bacteria colonize the mucus in a similar manner to the normal spiral-shaped microbiota. No evidence of adhesion to the intestinal surface was found with a wide variety of microscopic techniques. The campylobacters were seen to be highly motile in living preparations of gut tissue and rapidly tracked along intestinal mucus. Just as many of the normal spiral-shaped bacteria of intestinal surfaces can achieve close association with the epithelium through mucus association and do not adhere to the surface, C. jejuni colonizes the intestinal mucosa via mucus colonization. Thus, a major determinant of pathogenicity in intestinal infection with C. jejuni is proposed to be an ability to colonize intestinal mucus. The possession of specific adhesins is unlikely to be a significant determinant of pathogenicity. Better understanding of the mechanism of mucus association and the properties of the bacterium that are responsible will provide a basis for the rational selection of preventative measures. The model of mucus association in adult antibiotic-treated mice provides an opportunity for colonization studies with variant organisms and immunization studies.

The various layers of the cell envelope of marine pseudomonad B-16 (ATCC 19855) have been separated from the cells and assayed directly for alkaline phosphatase activity under conditions established previously to be optimum for maintenance of the activity of the enzyme. Under conditions known to lead to the release of the contents of the periplasmic space from the cells, over 90% of the alkaline phosphatase was released into the medium. Neither the loosely bound outer layer nor the outer double-track layer (cell wall membrane) showed significant activity. A small amount of the alkaline phosphatase activity of the cells remained associated with the mureinoplasts when the outer layers of the cell wall were removed. Upon treatment of the mureinoplasts with lysozyme, some alkaline phosphatase was released into the medium and some remained with the protoplasts formed. Cells washed and suspended in 0.5 M NaCl were lysed by treatment with 2% toluene, and 95% of the alkaline phosphatase in the cells was released into the medium. Cells washed and suspended in complete salts solution (0.3 M NaCl, 0.05 M MgSO(4), and 0.01 M KCl) or 0.05 M MgSO(4) appeared intact after treatment with toluene but lost 50 and 10%, respectively, of their alkaline phosphatase. The results suggest that the presence of Mg(2+) in the cell wall is necessary to prevent disruption of the cells by toluene and may also be required to prevent the release of alkaline phosphatase by toluene when disruption of the cells by toluene does not take place.

Kanamycin production by Streptomyces kanamyceticus ATCC 12853 requires magnesium sulfate and potassium phosphate at concentrations of 0.4 and 1.0 g per liter, respectively. The optimal concentrations of Fe and Zn for production of kanamycin are 0.25 and 0.575 mug/ml, respectively, whereas Mo at 0.04 mug/ml allows maximal cellular growth and antibiotic synthesis. Mn and Ca are without any effect. Cu, Co, Ni, and V have inhibitory effect on growth of the organism as well as kanamycin formation.

The phospholipid headgroup and fatty acid compositions of a halotolerant Planococcus sp. (strain A4a) were examined when cells were grown in the presence of high concentrations of a variety of salts. The fatty acid composition of Planococcus sp. strain A4a was altered primarily as a function of the osmolality of the growth medium. The phospholipid headgroup composition was influenced by both the osmolality of the growth medium and the nature of the cation species present. An increase in the cardiolipin/phosphatidylglycerol molar ratio was detected when cells were grown in the presence of high concentrations of monovalent cations.

The steady-state twist of Bacillus subtilis macrofibers produced by growth in complex medium was found to vary as a function of the magnesium and ammonium concentrations. Four categories of macrofiber-producing strains that differed in their response to temperature regulation of twist were studied. Macrofibers were cultured in the complex medium TB used in previous experiments and in two derivative media, T (consisting of Bacto Tryptose), in which most strains produced left-handed structures, and Be (consisting of Bacto Beef Extract), in which right-handed macrofibers arose. In nearly all cases, increasing concentrations of magnesium led to the production of macrofibers with greater right-handed twist. Some strains unable to form right-handed structures as a function of temperature could be made to do so by the addition of magnesium. Inversion from right- to left-handedness in strain FJ7 induced by temperature shift-up was blocked by the addition of magnesium. The presence of magnesium during a high-temperature pulse did not block the establishment of "memory," although it delayed the initiation of the transient inversion following return to low temperature. The twist state of macrofibers grown without a magnesium supplement was not instantaneously affected by the addition of magnesium. Such fibers were, however, protected from lysozyme attack and associated relaxation motions. Lysozyme degradation of purified cell walls (both intact and lacking teichoic acid) was also blocked by the addition of magnesium. Ammonium ions influenced macrofiber twist development towards the left-hand end of the twist spectrum. Macrofiber twist produced in mixtures of magnesium and ammonium was strain and medium dependent.(ABSTRACT TRUNCATED AT 250 WORDS)

Pseudomonas aeruginosa was found to be able to hydrolyze bile sulfate. This property was observed when lithocholate sulfate was substituted for the sulfur source in the culture medium. The addition of MgSO4 to the medium inhibited the hydrolysis of the bile sulfate.

The motility of Spirillum volutans is caused by the rotation of each polar flagellar fascicle in a direction opposite to that of the more slowly rotating cell. Both flagella form cones of revolution oriented in the same direction. When the cell reverses its motion, both fascicles simultaneously reverse their rotation and also the orientation of their cones of revolution, with the tail fascicle becoming the head and vice versa. Chloral hydrate and phenol were found to cause uncoordination, with both fascicles becoming the head type; MgSO(4), Mg(NO(3))(2), NiSO(4), NiCl(2), CuSO(4), and CuCl(2) also caused uncoordination, with both fascicles becoming the tail type. In all cases, the flagellar fascicles remained highly active but the cells were motionless because of the opposing propulsion; the rotation of the fascicles was in a constant direction without reversal. Uncoordinated states could be maintained for 30 to 60 min. Neutralization of the dual-tail flagellation caused by NiSO(4) could be accomplished with chloral hydrate. At the null point, the flagellar orientation was intermediate between head and tail; the fascicles continually reversed direction of rotation, and, now coordinated, caused the cells to move back and forth. Higher concentrations of chloral hydrate completely overcame the effect of NiSO(4) and caused dual-head flagellation. Optimal concentrations of test compounds were determined with the use of pure cultures and a reproducible growth medium.

An experimental investigation established the effect of the presence of inorganic salts on the foam separation of Pseudomonas fluorescens and of Bacillus subtilis var. niger (B. globigii) from aqueous suspension by use of a cationic surfactant. For P. fluorescens, 5.0 mueq/ml of NaCl, KCl, Na(2)SO(4), K(2)SO(4), CaCl(2), CaSO(4), MgCl(2), or MgSO(4) produced increases in the cell concentration in the residual suspension (not carried into the foam) from 2.9 x 10(5) up to 1.6 x 10(6) to 2.8 x 10(7) cells per milliliter (initial suspensions contain from 3.3 x 10(7) to 4.8 x 10(7) cells per milliliter). The exceptional influence of magnesium was overcome by bringing the cells into contact first with the surfactant and then the salt. For B. subtilis, the presence of 5.0 mueq/ml of any of the eight salts increased the residual cell concentration by one order of magnitude from 1.2 x 10(4) to about 4.0 x 10(5) cells per milliliter. This occurred regardless of the sequence of contact as long as the surfactant contact period was sufficient. The presence of salts increased collapsed foam volumes with P. fluorescens and decreased collapsed foam volumes with B. subtilis.

Magnesium sulfate and spermidine were tested for their effects on binding of (14)C-ethambutol by Mycobacterium smegmatis. Concentrations were used that protected the organism from ethambutol inhibition. Sodium salts were examined as possible ethambutol antagonists to test the previously reported specificity of the divalent cation salt effect. Consistent with growth-protection experiments, 20 mM MgSO(4) or 2.0 mM spermidine prevented and reversed (14)C binding by cells shaken with 0.2 mug of (14)C-ethambutol per ml of Sauton medium at 37 C. Sodium salts were not effective ethambutol antagonists when tested at 20 mM, but at concentrations equivalent in ionic strength (mu) to that provided by 20 mM MgSO(4) they were effective. Thus, 20 mM MgSO(4), 80 mM NaCl, or 27 mM Na(2)SO(4) (mu = 0.08) all gave similar results in growth protection and binding experiments, suggesting that MgSO(4) antagonism is a nonspecific ionic effect. Because spermidine (mu

The removal of washed and standardized Escherichia coli from distilled-water suspension by foam separation with nitrogen gas and 30 mug/ml of ethylhexadecyldimethylammonium bromide surfactant was increased by increasing the gas rate from 4.3 to 9.3 liters per min and by lowering the port level at which foam was removed from 60.4 to 20.4 cm, but with concomitant increases in foam volumes. The concentrations of cells and of surfactant in the residual suspensions were related to foam volumes; a given number of cells adsorbed a constant amount of surfactant. The addition of from 10 to 500 mug/ml of inorganic salts decreased the total cell removal, with magnesium sulfate producing an anomalously large effect. The addition of surfactant in several doses (compared with a single dose) together with an increase in foaming time from 10 to 24 min produced residual suspensions with lower cell concentrations, and, when salts were present in the initial suspensions, produced lower foam volumes and more concentrated foams.

The Beaudette strain of avian infectious bronchitis virus propagated in chicken embryo kidney cells is stabilized by exposure to 1 M MgSO(4) at 50 C for 80 min, at pH values ranging from 4 to 10.

The sensitivity of Escherichia coli to the lethal effect of colicin E(2) was reduced by elevation of osmotic pressure of the incubation medium. Optimal protection of the cells from the lethal effect of colicin E(2) was achieved with 0.6 to 0.8 m NaCl or with 0.8 m sucrose containing 0.01 m MgSO(4). Under such conditions, the degradation of deoxyribonucleic acid caused by colicin E(2) was also suppressed markedly. It was concluded that a high concentration of sucrose with Mg(++) might prevent the action of the adsorbed colicin E(2). A similar protection was observed against the lethal effect of colicin K.

Suspensions of cells of a marine pseudomonad washed with 0.05 m MgSO(4) showed an immediate increase in optical density (first-phase optical change) when the salt concentration of the suspending medium was increased; a subsequent slow decrease in optical density (second-phase optical change) occurred if K(+) was present. The rate of the second-phase change was similar to the rate of uptake of (42)K(+) by the cells. Glutamate increased the rate and extent of the second-phase change and produced a parallel increase in the rate and extent of uptake of (42)K(+). Citrate increased the extent of the second-phase change in cells adapted to oxidize citrate but not in unadapted cells. Adapted, but not unadapted, cells accumulated (14)C-citrate. The nonmetabolizable alpha-aminoisobutyric acid (AIB) also increased the extent of the second-phase change under conditions leading to the uptake of (14)C-AIB by the cells. Cells maintained in a salt solution optimal for the retention of intracellular solutes were found to contain 0.184 m K(+). In the same salt solution, cells preloaded with (42)K(+) retained the isotope, but they lost it rapidly when suspended in 0.05 m MgSO(4). The second-phase changes can be accounted for by the energy-dependent accumulation in an osmotically active form of K(+) and other metabolites by cells depleted of intracellular solutes.

Protoplast formation by Histoplasma capsulatum yeasts using high concentrations of MgSO(4) occurs either by lysis of the bud or lysis of the entire cell wall. Both mechanisms may also occur simultaneously. Neither the protoplast emerging through a hole in the cell wall nor the freshly released protoplast has a recognizable cell wall or the remnant of such. The protoplast contains all the organelles of the normal cell except for mesosomes. During protoplast formation the nucleus increases in size and produces several nuclear masses by the invaginations of the internal layer of the nuclear membrane. All these nuclear masses are surrounded by the external layer of the nuclear membrane. Several nuclei with a normal nuclear membrane are formed later.

L forms were induced from 15 of 16 strains of Listeria monocytogenes on penicillin gradient plates incubated under aerobic conditions. The culture medium for maintenance of these L forms must contain an electrolyte in a concentration of 1% or sucrose in a concentration of 10%. The electrolytes NaCl, KCl, or MgSO(4) were used in both induction and maintenance media. Induction of L forms occurred more rapidly on media containing KCl. Listeria L forms had the same fermentation reactions as the parent bacterium. The L-form growth in liquid medium was slow, not extensive, and appeared as clumps on the bottom of culture tubes. The morphology of Listeria L forms was similar to that reported for other bacterial L forms. The L forms derived from strain 10403, serotype 1, were stable after two or more passages on penicillin media. They did not revert to the bacterial form after 40 subcultures on penicillin-free media. Some L-form colonies derived from strain 10403 did revert to the bacterial form when transferred directly from induction plates to penicillin-free media. Studies of the growth characteristics for L forms derived from strain 10403 gave the following results: an optimal temperature of 30 C, high electrolyte or sucrose concentration necessary for induction and maintenance, and no requirement for serum.

In Sauton's synthetic liquid medium, 10 mug of pyridoxal per ml completely protected Mycobacterium tuberculosis (H37R(a)) from the effects of a minimal inhibitory concentration of isoniazid (0.01 mug/ml). (14)C-labeled isoniazid was employed to study the nature of this protective effect. Uptake of the drug by cells in a Sauton environment containing 0.01 mug of (14)C-isoniazid per ml was inhibited 20 to 40% by 10 mug of pyridoxal per ml during the early hours of drug exposure. A stronger inhibition of uptake resulted when labeled isoniazid and pyridoxal were increased to 0.1 mug/ml and 50 to 100 mug/ml, respectively. Further studies revealed that certain Sauton nutrients are required to achieve this effect. When l-asparagine or salts (MgSO(4) and ferric ammonium citrate) or both were deleted from the menstruum, pyridoxal did not inhibit isoniazid incorporation by the tubercle bacilli. Pyridoxal also failed to inhibit uptake when (NH(4))(2)SO(4) was substituted for l-asparagine. Growth experiments in Sauton's medium modified to contain (NH(4))(2)SO(4) instead of l-asparagine were consistent with the latter finding. Pyridoxal did not prevent isoniazid growth inhibition in this medium. It is postulated that a large excess of pyridoxal in Sauton's medium protects tubercle bacilli from the effects of isoniazid through formation of an extracellular complex involving drug, vitamin, and certain medium constituents, thereby reducing the level of isoniazid available to the cells.

Previous studies have indicated that a single enzyme, "kynureninase," catalyzes the reactions of l-kynurenine to anthranilate and l-3-hydroxykynurenine to 3-hydroxyanthranilate in Neurospora crassa and in other organisms. The present report describes separate enzymes which catalyze these reactions in N. crassa. The first, a kynureninase, preferentially catalyzes kynurenine to anthranilate and is induced over 400-fold by tryptophan or a catabolite of tryptophan. The second, a hydroxykynureninase, is constitutive or noninducible by tryptophan and preferentially catalyzes l-3-hydroxykynurenine to 3-hydroxyanthranilate. The physiological significance of these enzymes may be inferred from the facts that (i) the noninducible enzyme hydroxykynureninase appears to be the main enzyme present in uninduced cells that is capable of catalyzing l-3-hydroxykynurenine to 3-hydroxyanthranilate for the indispensible synthesis of nicotinamide adenine dinucleotide, and (ii) the inducible enzyme kynureninase is induced by tryptophan to a concentration far in excess of that needed to meet the requirements of the cells for nicotinamide adenine dinucleotide, resulting in the excretion of anthranilate into the medium.