Induction Of Lysis Research Articles

IgG-Fc-receptors: ligand binding and lysis induction

Abstract Fc receptors (FcR) are immunoglobulin (Ig) binding structures reacting with the Fc part of the anti-body molecules (reviewed in [1–2]). A wide range of cells express FcRs, most of them belonging to the cells of the immune system including monocytes, macrophages, granulocytes, K cells, B cells some T cells; but FcRs are present on membranes of other cell types as well. The FcRs expressed on cells of the immune system play important roles in immunological processes, such as phagocytosis of opsonized particles, clearance of immune complexes, antibody-dependent cellular cytotoxicity (ADCC), regulation of immune response, and mediation of signals for production of inflammatory mediators. FcRs are structurally and functionally very heterogenous. Their heterogeneity manifests itself in binding of different isotypes of Igs, as well as in mediation of various functional activities. Due to the heterogeneity of FcR-bearing cells, to the structural heterogeneity of FcRs themselves and, more-over to the difficulties in isolation and purification of the receptors to homogeneity, most of the biochemical studies on FcR structure have resulted in conflicting results. The application of monoclonal antibodies with anti-FcR specificity and the cloning of FcR genes led to the real breakthrough in the structural analysis of FcRs. The poly-Ig FcR was the first FcR of which the genes were cloned. It turned out that the poly-Ig FcR has repeating Ig-like domains; five extracellular domains, a membrane-spanning portion, and a cytoplasmic tail. Four of the five extracellular domains are similar to the Ig KV, Ig HV domains and Thy-1 antigen, whereas the fifth domain resembles an Ig constant domain [3]. Recently several other FcRs have been cloned and it turned out that IgG FcRs show structural similarity to the Igs, i.e., they belong to the group of proteins known as the Ig superfamily [2]. Using monoclonal antibodies recognizing FcRs, three classes of the human IgG-binding structure — FcRI, FcRII and FcRIII - have been defined by Anderson and Looney [4]. The three receptors were found to be expressed on distinctive and overlapping populations of cells. FcRI (molecular weight about 72 kDa) is expressed only on mononuclear phagocytes The rank of order of affinity of FcRI for the IgG subclasses is IgG1 = IgG2>IgG4, while it does not interact with IgG2. FcRII (40 kDa) is present on a wide range of cells, including monocytes, neutrophils, eosinophils, platelets and B cells. It binds IgG1 and IgG3 (evaluated on platelets) with high affinity and equally well, while less readily with the other subclasses. FcRIII, the low affinity IgG binding receptor (50–70 kDa) expressed on neutrophils, eosinophils, macrophages, NK, and K cells, shows preferential binding of IgG1 and IgG3. The three distinct FcRs bind IgG subclasses of mouse origin as well, but the specificity of binding is quite distinctive. Based on resulted of gene cloning (reviewed in [2]) the FcRI binding monomeric IgG with high affinity seems to contain three extracellular Ig-like domains. Three forms of FcRII have been characterized (FcRIII A, B and C). Similarity to the equivalent murine IgG2b/1 binding FcR, 90–95% homology between

Lysis induction of Escherichia coli by the cloned lysis protein of the phage MS2 depends on the presence of osmoregulatory membrane-derived oligosaccharides.

Expression of the cloned lysis protein of phage MS2, which is sufficient to lyse wild type Escherichia coli, does not cause lysis of mutants lacking the osmoregulatory membrane-derived oligosaccharides (MDO). The lysis gene product normally found in the membrane fraction was not stably inserted into the membranes of a mdoA mutant; rather degradation and release from the membrane occurred. Gentle plasmolysis of the MDO-lacking mutant clearly showed an increased periplasmic space as compared to wild type cells. It is concluded that the MDOs play an important role in maintaining a proper arrangement of inner and outer membrane, a prerequisite for a functional insertion of the MS2 lysis protein.

Autolytic system of Staphylococcus simulans 22: influence of cationic peptides on activity of N-acetylmuramoyl-L-alanine amidase

Pep 5 and nisin are cationic peptide antibiotics which in addition to their membrane-disruptive action induce autolysis in staphylococci. To investigate the mechanism of lysis induction, the influence of the peptides on the activity of the N-acetylmuramoyl-L-alanine amidase of Staphylococcus simulans 22 was studied. In experiments with isolated cell walls at low ionic strength, the amidase activity was stimulated by the addition of Pep 5 and nisin, as well as by polylysine, streptomycin, and mono- and divalent cations. The concentrations necessary for activation depended on the nature of the cation and ranged from 5 microM for poly-L-lysine (n = 17) to 150 mM for Na+ at a cell wall concentration of 100 micrograms of cell walls per ml. No effect was observed if the cell walls were devoid of polyanionic constituents. Kinetic data suggested that the amidase bound to the teichoic and teichuronic acids of the cell wall and was thereby inhibited. Cationic molecules reversed this inhibition, most likely by displacing the enzyme from the polyanions. If the concentrations of the larger peptides were high in relation to cell wall concentration, the activation turned into inhibition, presumably by interfering with the access of the enzyme to its substrate. These experiments demonstrate that the activity of the amidase is modulated by basic peptides in vitro and help to explain how Pep 5 and nisin may cause lysis of treated cells.

Identification of monoclonal antibodies specific for the T cell receptor complex by Fc receptor-mediated CTL lysis.

Monoclonal antibodies (mAb) directed at the T cell receptor complex (TcR) on cloned T cells have generally been identified by their ability to inhibit the clone's antigen-specific function. Because such inhibition is highly dependent on antibody concentration and affinity, detection of anti-clonotypic antibodies to murine alloreactive T cells has been very difficult. In this report, an alternative method is described on the basis of the ability of antibodies specific for the TcR complex to activate T cells in an antigen-independent manner. The assay is based upon the observation that soluble antibodies to human T3 promote lysis of irrelevant, Fc receptor-positive targets by a human CTL line. By using this approach, an anti-TcR mAb has been identified among a panel of murine mAb generated against an alloreactive CTL clone. Induction of lysis by soluble anti-TcR mAb has been shown to require both the expression of Fc receptors on the target cell and conjugate formation between the effector and the target cell. This assay provides a screening procedure that is much more sensitive than inhibition of function, and it preferentially detects antibodies specific for cell surface molecules involved in T cell activation.

Involvement of penicillin-binding protein 2 with other penicillin-binding proteins in lysis of Escherichia coli by some beta-lactam antibiotics alone and in synergistic lytic effect of amdinocillin (mecillinam).

Compared with cefotaxime, ceftazidime, moxalactam, and aztreonam, ceftriaxone produced the best lytic and bactericidal effects when each was added at about 10 times the MIC to Escherichia coli W7. When each of these antibiotics was added at its MIC, only bacteriostasis occurred, but the simultaneous addition of amdinocillin (mecillinam) was synergistic in causing rapid lysis and bactericidal effects. Induction of lysis of two E. coli mutants containing either a thermosensitive penicillin-binding protein (PBP) 2 or 3 by relatively PBP 3-specific (aztreonam) and PBP 2-specific (amdinocillin) antibiotics indicated that inhibition of only PBPs 2 and 3 can cause lysis. Examination of the interactions of cefotaxime, aztreonam, and cefsulodin, with or without amdinocillin, with their targets suggested that other combinations of PBPs could be involved in the onset of lysis. However, inhibition of both PBPs 2 and 3 may explain the better lysis-inducing activity of ceftriaxone (which binds well to both of these PBPs), as well as the synergistic effect of amdinocillin when added together with low concentrations of other beta-lactam antibiotics that interact with PBP 3.

Induction and blocking of cytolysis in CD2+, CD3- NK and CD2+, CD3+ cytotoxic T lymphocytes via CD2 50 KD sheep erythrocyte receptor.

The 50 KD sheep red blood cell antigen receptor CD2 is the earliest T cell differentiation marker and is present on all blood-derived T cells, including natural killer (NK) cells. The CD2 antigen is also known to serve as an important activation site regulating various T cell functions. We report that anti-CD2 monoclonal antibodies (MAb) block MHC-restricted class I- and class II-specific cytolysis by CD2+, CD3+ clones of the relevant target cells, irrespective of whether lysis by these clones is blocked by anti-CD3 or anti-CD8 MAb. Moreover, anti-CD2 MAb (but not anti-CD3 MAb) are able to reduce MHC-nonrestricted, nonspecific cytolysis: a) by CD2+, CD3+ clones of K562 target cells; and b) by CD2+, CD3 NK clones of K562 as well as Daudi cells. Different preparations of anti-CD2 MAb vary in their capacity to inhibit cytolysis. For cloned effector cells, the percent inhibition of lysis by CLB-T11 greater than Lyt-3 MAb, whereas with "fresh" NK cells, the lysis inhibitory ability of Lyt-3 greater than CLB-T11. The antibody-dependent cellular cytotoxicity by "fresh" and cloned NK cells is not inhibited by anti-CD2 MAb. Anti-CD2 MAb also prevent the induction of lysis by cross-linked anti-CD3 MAb, e.g., by CD2+, CD3+ cloned cloned cells against (IgG-FcR+) Daudi cells. Anti-CD2 MAb can also induce cytolysis in some, but not all, CD2+, CD3- NK clones against xenogeneic P815 mouse mastocytoma cells. Anti-CD2 MAb, in combination with lectins (PHA or Con A: pretreatment of effector cells), can also induce cytolytic activity by CD2+, CD3+ clones against Daudi cells. Our data therefore support the concept that the CD2 antigen is an important activation site regulating a wide variety of T cell functions including cytolysis. Whether ligand interaction with the CD2 antigens results in augmentation or inhibition of T cell functions may very well depend on the type of CD2 antigen-ligand interaction, e.g., cross-linked ligand-receptor interaction may, in general, enhance the various T cell functions, whereas noncross-linked ligand-receptor interactions may inhibit such functions, as we and other investigators demonstrated earlier for the CD3/Ti antigen-receptor complex activation site.

Differential induction of Escherichia coli autolysis by penicillin and the bacteriophage phi X174 gene E product.

The behavior of the temperature-sensitive, penicillin-tolerant Escherichia coli mutant VC44 to endogenously induced autolysis by the bacteriophage phi X174 gene E product (gpE) was investigated. Expression of the cloned phi X174 lysis gene showed that cultures of strain VC44 grown at the restricted temperature were fully sensitive to endogenously induced autolysis. The results revealed that the modes of E. coli lysis induction by gpE and by penicillin differ and that the trigger mechanisms for autolysis depend greatly on the specific inducer used.

Induction of autolysis of staphylococci by the basic peptide antibiotics Pep 5 and nisin and their influence on the activity of autolytic enzymes

Pep 5 and nisin are cationic bactericidal peptides which were shown to induce autolysis in Staphylococcus cohnii 22. In contrast to nisin, Pep 5 induced lysis could be stimulated in the presence of glucose. Addition of lipoteichoic acids (LTA) (D-alanine:phosphorus = 0.475:1) inhibited all effects of Pep 5 on susceptible cells in a molar ratio LTA:Pep 5 of 10:1. Treatment of S. cohnii 22 with Pep 5 or nisin for 20 min and subsequent washing with 2.5 M NaCl released autolysin activity. Crude preparations of the hydrolyzing enzymes produced free amino groups as well as polysaccharide fragments from the murein backbone, suggesting the presence of a muramidase or glucosamidase, and endopeptidase or amidase. Both enzyme activities were inhibited by lipoteichoic acid; they could be fully reactivated by addition of Pep 5 in sufficient concentrations. The velocity of hydrolysis was not influenced by nisin, whereas it was doubled in presence of Pep 5. The results are discussed in view of a possible mechanism of induction of lysis by Pep 5 and nisin.

The O R control system of bacteriophage lambda : A physical-chemical model for gene regulation

A quantitative model has been developed for processes in the bacteriophage lambda that control the switchover from lysogenic to lytic modes of growth. These processes include the interactions of cI repressor and cro proteins at the three DNA sites of the right operator, O R, the binding of RNA polymerase at promoters P R and P RM, the synthesis of cI repressor and cro proteins, and the degradative action of recA during induction of lysis. The model is comprised of two major physical-chemical components: (1) a statistical thermodynamic theory for relative probabilities of the various molecular configurations of the control system; and (2) a kinetic model for the coupling of these probabilities to functional events, including synthesis of regulatory proteins cI and cro. Using independently evaluated interaction constants and rate parameters, the model was found capable of predicting essential physiological characteristics of the system over an extended time. Sufficiency of the model to predict known physiological properties lends credence to the physical-chemical assumptions used in its construction. Several major physiological characteristics were found to arise as “system properties” through the non-linear, time-dependent, feedback-modulated combinations of molecular interactions prescribed by the model. These include: (1) maintenance of the lysogenic state in the absence of recA-mediated cI repressor degradation; (2) induction of lysis and the phenomenon of subinduction; and (3) autogeneous negative control of cro. We have used the model to determine the roles, within the composite system, of several key molecular processes previously characterized by studies in vitro. These include: (1) co-operativity in cI repressor binding to DNA; (2) interactions between repressors and RNA polymerase (positive control); and (3) the monomer-dimer association of cI repressor molecules. A major role of cI repressor co-operativity is found to be that of guaranteeing stability of the lysogenic state against minor changes in cI repressor levels within the cell. The role of positive control seems to be that of providing for a peaked, rather than monotonie, dependence of P RM activity on cI repressor level, while permitting P R activity to be a step function. The model correlates an immense body of studies in vivo and in vitro, and it makes testable predictions about molecular phenomena as well as physiological characteristics of bacteriophage lambda. The approach developed in this study can be extended to include more features of the lambda system and to treat other systems of gene regulation.

Effects of chlordecone and its alteration products on isolated rat liver mitochondria

Partitioning of chlordecone, chlordecone alcohol, monohydrochlordecone, and dihydrochlordecone (2 to 100 μ m) into isolated rat liver mitochondria altered the permeability properties of the inner membrane as evidenced by: inhibition of valinomycin-induced swelling, induction of passive swelling, oxidation of exogenous NADH, and induction of lysis. Associated with the increase in permeability were stimulation of state 4 and inhibition of state 3 respiration for the oxidation of both succinate and glutamate. Except for the inhibition of valinomycin-induced swelling, the following order of potency for all assays was obtained: chlordecone alcohol ≥ chlordecone > monohydrochlordecone ⪢ dihydrochlordecone. Mirex, a 12-chlorine analog of chlordecone, and a dioxolanechlordecone adduct did not affect any of the reactions at saturating concentrations of 40 and 100 μ m, respectively. The hydrated ketone, or a hydroxyl moiety, and a high chlorine content appear to be responsible for lytic and inhibitory activity. Lysis resulted in the leakage of watersoluble matrix enzymes from the mitochondria, but not in the solubilization of integral proteins.

Effect of leukocyte hydrolases on bacteria XVI. Activation by leukocyte factors and cationic substances of autolytic enzymes in Staphylococcus aureus: modulation by anionic polyelectrolytes in relation to survival of bacteria in inflammatory exudates.

The mechanisms involved in the activation of autolytic enzymes in Staphylococcus aureus, by leukocyte extracts, cationic proteins, phospholipase A2, amines, and membrane-damaging agents was studied in a resting cell system as well as by growing staphylococci. The bacteria were labeled with [14C]N-acetylglucosamine and were subjected to a variety of agents either in 0.1 M acetate buffer, pH 5.0, or in phosphate buffer, pH 7.4. While intact log-phase cultures were found to undergo partial autolysis at pH 5.0 and almost complete lysis at pH 7.4, both heat-killed bacteria and bacterial cell walls were completely resistant to autolysis in buffers. Autolysis at pH 5.0 can be further activated by leukocyte extracts, nuclear histone, crystalline ribonuclease, egg-white and human lysozyme, phospholipase A2, as well as by spermine, spermidine, and polymyxins B and E. The addition of viable log-phase bacteria to radiolabeled heat-killed staphylococci or to radiolabeled cell walls which had been cleaned off autolytic enzymes resulted in degradation of the radiolabeled targets. The data suggest that the various inducers of autolysin activation caused leakage of autolytic enzymes from the intact bacteria which attacked the depolymerized the bacterial cell walls. Anionic polyelectrolytes like heparin, dextran sulfate, suramine, polyglutamic acid, and liquid (polyanethole sulfonic acid) markedly inhibited both spontaneous and induced lysis. Staphylococci which had grown in the presence of anionic polyelectrolytes became highly resistant to lysis triggered by any of the inducers of autolysis. Since inflammatory exudates are known to be rich in anionic polyelectrolytes, it is suggested that the prolonged survival of intact bacterial cells in such a milieu may be due to the inactivation of autolytic enzymes. It is also postulated that the degradation of certain bacterial species following phagocytosis or extracellular degradation may not be the result of the action of hydrolytic enzymes but rather the result of activation by leukocyte factors of autolytic enzymes which lead to bacteriolysis.

Alternative Complement Pathway-Mediated Lysis of Measles Virus Infected Cells: Induction by IgG Antibody Bound to Individual Viral Glycoproteins and Comparative Efficacy of F(ab′)2 and Fab′ Fragments

Abstract Lysis of measles virus-infected cells by human serum is dependent on IgG antibody and an intact alternative complement pathway. The binding sites of IgG measles virus antibody, or its fragments, on the surface of measles virus-infected cells were determined by cell surface radioiodination and immunoprecipitation. It was found that IgG bound to either of the two measles virus surface glycoproteins was effective in inducing cell lysis by the alternative pathway. Thus, IgG bound only to the viral hemagglutinin (HA) or only to the fusion protein (F) could induced lysis in C4-depleted human serum; the same number of IgG molecules bound to either HA or F induced equivalent dose-related lysis. Divalent antibody bound preferentially to HA on the surface of intact cells; this enabled antibody to F to be obtained free of antibody to HA by adsorption. Quantitative studies of binding and lysis showed that lysis of measles virus-infected cells by whole or C4-depleted serum required binding of at least 10 times more Fab′ than F(ab′)2 or IgG molecules per cell. In these experiments, C4-depleted serum was quantitatively and kinetically equivalent to whole serum in mediating lysis of measles-infected cells. Hence, the binding of IgG to either of the two measles viral polypeptides (HA, F) expressed on the surface of infected cells induces lysis by the alternative pathway, and there is a clear requirement for divalency for effective induction of lysis.

The release of carbohydrates during mating in Chlamydomonas reinhardi

During mating of gametes of the alga Chlamydomonas reinhardi, certain physiological changes occur. These changes include the formation, in the (+) gamete, of a fertilization tubule and the release, in both mating types, of a lytic factor which removes cell walls. We have been able to quantitate the latter process, by measuring accumulation of released carbohydrates during the mating process. Contrary to published reports, we have found that glutaraldehyde-fixed gametes and isolated gametic flagella, though they cause the agglutination reaction, do not induce the lytic factor. This implies that induction of lysis takes place during the one-to-one (+) and (-) pairing that occurs subsequent to the initial massive agglutination.

Induction of Prophage in Lactic Streptococci Isolated from Commercial Dairy Starter Cultures

Twelve commercial dairy starter cultures were examined for presence of lysogens by treating isolated strains with ultraviolet irradiation or mitomycin C. Induction of lysis in isolates from nine of the 12 commercial cultures suggested the presence of lysogenic strains. No indicator organisms were detected, but presence of phage was confirmed by electron microscopy in two of the Streptococcus cremoris isolates from the commercial cultures. The results confirm that some commercial dairy cultures produced in the United States contain phage-harboring strains.

"Natural" killer cells in the mouse. I. Cytotoxic cells with specificity for mouse Moloney leukemia cells. Specificity and distribution according to genotype.

In the spleens of young, adult mice there exist naturally occurring killer lymphocytes with specificity for mouse Moloney leukemia cells. The lytic activity was directed against syngeneic or allogeneic Moloney leukemia cells to a similar extent, but was primarily expressed when tested against in vitro grown leukemia cells. Two leukemias of non-Moloney origin were resistant and so was the mastocytoma line P815. Although killer activity varied between different strains of mice, the specificity of lysis was the same as indicated by competition experiments using unlabeled Moloney or other tumor cells as inhibitors in the cytotoxic assays. Capacity to compete and sensitivy to lysis by the killer cells were found to be highly positively correlated. Analysis of the kinetics of the cytotoxic assay revealed a rapid induction of lysis within one to four hours, arguing against any conventional in vitro induction of immune response. No evidence was found of soluble factors playing any role in the cytolytic assay.

Polybase induced lysis of yeast spheroplasts

The polybasic macromolecules DEAE-dextran (diethylaminoethyl-dextran, molecular weight 500000) and poly-DL-lysine (molecular weight 30000-70000) were absorbed with a high affinity by spheroplasts of Candida utilis and subsequently, induced lysis. The extent of lysis of spheroplasts and of the liberated vacuoles was studied under various conditions using alpha-glucosidase activity and soluble arginine as cytoplasmic and vacuolar markers, respectively. Adsorption of polybases was rapidly completed even at 0 degrees C; however, with small doses, lysis was poor at 0-12 degrees C and extensive at temperatures above 12 degrees C. This permitted the completion of adsorption before initiating lysis. The purified vacuoles were also sensitive to polybases though less so than the spheroplasts; however, after lysis of spheroplasts the liberated vacuoles were well protected against the action of polybases. A treatment with polybases which disrupted more than 99% of the spheroplasts left at least 70% of the vacuoles intact. Potassium chloride in high concentrations and calcium chloride in low concentrations inhibited polybase induced lysis of spheroplasts by preventing or even reversing the polybase adsorption. A polyacidic macromolecule, dextran sulfate, could prevent but not reverse the adsorption of polybase and subsequent lysis. Metabolic inhibitors reduced the susceptibility of spheroplasts to polybase induced lysis. Vacuoles isolated from polybase lysed spheroplasts still contained large pools of soluble amino acids, and their ability to transport arginine specifically is a further indication of their functional integrity.

FOUR NEW HL‐A ALLELIC FACTORS SUBTYPIC TO HL‐A12 AND W15. THEIR CORRELATION WITH W4 AND W6

SUMMARYSeveral anti‐HL‐A antisera, correlated with either HL‐A12 or W15, were studied. Immunogenetic analysis was carried out by population and family studies, adsorptions, elutions and resistance to lysis induction capacity. Antibodies present in the sera allow the distinction to be made between two alternative factors subtypic to HL‐A12,‘TO 50’and‘TO 51′, and two alternative factors subtypic to W15,‘TO 52’and‘TO 53′. These subdivisions are genetically determined. Lysostrip experiments demonstrated them to be on the same molecule carrying either HL‐A 12 or W15. Thus, they enable the identification of new locus FOUR allelic products. These new HL‐A factors are strictly correlated with W4 and W6: haplotypic association has regularly been found between TO 50 and W4, TO 51 and W6, TO 52 and W4, TO 53 and W6. This subdivision of HL‐A allelic products into specificities subtypic either to W4 or to W6 is a characteristic common to most, if not all, FOUR factors. Finally, the commonly observed cross‐reaction between W15 and W17 preferably takes place with TO 52. It should be noted that both TO 52 and W17 are subtypic to W4.

A replicative form of the DNA of minute virus of mice.

The growth of minute virus of mice (MVM) in L cells was followed by plaque assay of both cell-associated and free virus at intervals up to 36 h after infection. The major production of progeny virus occurred after incubation for 27 h and most of the virus remained cell-associated. L cells infected with MVM were pulse-labeled with 3H-thymidine for 6 h preceding induction of lysis with sodium dodecylsulfate. Two new species of DNA remained in the supernatant fractions from lysates after selective precipitation by 1 M NaCl of cellular DNA. These first appeared 17 h after infection. On the basis of sedimentation rates and response to heating and to treatment with alkali, one of these species is a hydrogen-bonded duplex molecule, which on denaturation hybridized with the single-stranded DNA of MVM virions.

Studies of the C3 shunt activation in cobra venom induced lysis of unsensitized erythrocytes.

A procedure is described to evaluate the activation of the C3 shunt through cobra venom factor-mediated lysis of unsensitized erythrocytes. Data pertaining to several parameters of this assay are given. These include the requirement for magnesium, inhibition by heparin and the effects of hydrazine. The available evidence also suggests that the mechanism of cobra venom interaction with serum factors such as C3 proactivator differs from that of immune aggregates or inulin.

Aflatoxin B1 induction of lysogenic bacteria.

A technique for biological verification of aflatoxin B(1) was developed based on toxin-mediated induction of lysis in a lysogenic strain of Bacillus megaterium NNRL B-3695. Reduction of culture turbidity was determined at various concentrations of toxin. Incubation of 1.1 x 10(-4) g (dry weight) of cells/ml of growth medium containing 25 mug of B(1) per ml at 37 C reduced initial turbidity 0.20 absorbance units in 4 hr. If the bacterial lysate of the lysogenic strain, after a 2-hr incubation with 25 mug of B(1) per ml, was plated with a sensitive B. megaterium strain (NRRL B-3694), plaque-forming units increased approximately 150 times relative to the control. Comparable testing of the effects of aflatoxin on the nonlysogenic, sensitive strain demonstrated that 75 mug of B(1) per ml neither induced lysis nor plaque-forming units. Although induction is not an exclusive property of aflatoxin B(1), the differential response of the lysogenic and sensitive Bacillus strains to B(1) offers a unique and rapid technique for biological verification of the toxin.