bluuebunny/crossref_metadata_2025_split huggingface dataset:
Production of pollution‐tolerant strains of unicellular algae through mutagenic treatment. I. Ethyl methane sulphonate
Authors: Kumar H. D. , Sharma Vasundhara , Bisaria G. P. 
Published: July 2010

AbstractThe unicellular algae Anacystis nidulans and Chlorella vulgaris were collected from effluents of the Indian Oil Refinery Barauni and the Sindri Fertilizer Factory (India), respectively, and isolated in unialgal and bacteria‐free culture.The algae were treated with the mutagen ethyl methane sulphonate and such mutagenically treated algae were compared with untreated controls with respect to growth characteristics and the capacity to absorb the two important components of polluted habitats, viz., phosphate and nitrate.Treated A. nidulans grew faster and showed a consistently higher uptake of phosphate than untreated. Treated C. vulgaris cells grew more slowly than untreated cells and showed lesser phosphate uptake during early phases of growth but greater uptake during the later phases.Nitrate uptake capacity was increased in both algae following treatment.
Regulative Beeinflussung der Nourseothricinbiosynthese durch O‐Aminobenzoesäure in Kulturen des Streptomyces noursei JA 3890b
Authors: Gräfe U. , Bocker H. , Reinhardt G. , Thrum H. 
Published: July 2010

AbstractThe biosynthesis of nourseothricin, a streptothricin type antibiotic, is strongly stimulated by o‐aminobenzoic acid in cultures of S. noursei JA 3890 b. o‐Aminobenzoic acid (OAB) was shown to interfere with the amino acid metabolism and to influence last not least the efficacy of the precursor supplying system in the antibiotic biosynthesis. Thus, mycelium cultivated in presence of OAB (7.5 mM) exhibits strongly increased activities of NADP‐specific glutamate dehydrogenase. Simultaneously, this effector prevents the induction of alanine dehydrogenase in productive cultures suggesting that an enhanced formation of alanine interferes with antibiotic biosynthesis. Insignificant variations of further enzymic activities, e.g. of transaminases, of phosphoenolpyruvate carboxylase and of enzymes of the tricarboxylic acid cycle were observed. Furthermore, the possible role of o‐aminobenzoic acid as an effector of metabolite transport systems or of energy metabolism is discussed.
Utilization of lipids as sole carbon sources by thermophilic fungi
Authors: Oso B. A. 
Published: July 2010

AbstractThe ability of six thermophilic fungi to utilize fatty acids and glycerol as sole carbon sources for growth was studied in liquid shake‐cultures at 45°C. These fungi, which were found occurring in stacks of oil palm kernels at the oil mills in Nigeria, included Chaetomium thermophile var. coprophile COONEY and EMERSON, Chaetomium thermophile var. dissitum COONEY and EMERSON, Mucor pusillus LINDT, Thermoascus aurantiacus MIEHE sensu APINIS, Thermoascus crustaceus (APINIS and CHESTERS) STOLK, and Humicola lanuginosa (GRIFFON and MAUBLANC) BUNCE. All the organisms produced the best growth on stearic, palmitic, oleic, and myristic acids with the exception of C. thermophile var. coprophile which did not grow on myristic acid. They all had an average growth on behenic, acetic, butyric, and valeric acids with the exception of T. crustaceus and H. lanuginosa which did not utilize butyric acid, and M. pusillus and H. lanuginosa which produced no growth on valeric acid. The other fatty acids tested, capric, caprylic, lauric, linoleic, and arachidic acids, were not available to any of them, while glycerol was utilized by all. The six organisms produced good growth and indicated acid production on a Nile blue sulphate/groundnut oil medium. Their involvement in the biodeterioration of oil palm produce during processing and in storage was suggested.
Wirkung von Ammoniumhumat auf einige Virus‐Zell‐Systeme
Authors: Klöcking Renate , Sprössig M. 
Published: July 2010

AbstractEs wird die Wirkung von Ammoniumhumat auf die Vermehrung von 3 RNS‐Viren (Coxsackievirus A9, Influenzavirus A2, ECHO‐Virus Typ 6) und 3 DNS‐Viren (Herpes‐simplex‐Virus Typ 1, Adenovirus Typ 2, Vakziniavirus) geprüft. Als humatempfindlich erweisen sich — in der Reihen‐folge ihrer Hemmbarkeit — Herpes‐simplex‐Virus Typ 1 > Influenzavirus A2 > Coxsackievirus A9. Dagegen wird die Vermehrung von ECHO‐Virus Typ 6, Adenovirus Typ 2 und Vakziniavirus nicht oder kaum beeinflußt. Für Herpes‐simplex‐Virus Typ 1 wird ein Eingreifen des Humates in die Adsorptionsphase des Virus nachgewiesen und die Hemmung eines späteren, für die Virus‐synthese erforderlichen Stoffwechselschrittes wahrscheinlich gemacht.
Einfluß freier Fettsäuren auf die Aktivität von Enzymen des Citrat‐ und Glyoxylatzyklus aus Acinetobacter calcoaceticus
Authors: Kleber H.‐P. , Göbel H. 
Published: July 2010

AbstractDer Einfluß von freien Fettsäuren der Kettenlänge C6—C12 auf die Aktivität der Enzyme des Citratzyklus (Citratsynthase, Aconitase, Isocitratdehydrogenase, Fumarase, Malatdehydrogenase), des Glyoxylatzyklus (Isocitratlyase) sowie des Malatenzyms aus Acinetobacter calcoaceticus wird untersucht.Durch freie Fettsäuren wird nur das Malatenzym gehemmt. Die Fettsäuren hemmen das Enzym gegen L‐Malat kompetitiv nichtlinear. Die graphisch ermittelten KI‐Werte nehmen in der homologen Reihe der Fettsäuren von der Hexansäure (KI = 1,0 × 10−2 M) zur Dodecansäure (KI = = 3,0 × 10−4 M) ab. Die durch Fettsäuren bedingte Hemmung des Malatenzyms ist abhängig vom pH‐Wert.
Untersuchungen an T3‐Phagen. VII. Cross streak‐Komplementierung von temperatursensitiven
Authors: Krüger D. H. , Scholz D. , Rosenthal H. A. 
Published: July 2010

AbstractTemperature‐sensitive (ts) mutants of phage T3 were isolated following mutagenesis with nitrosoguanidine. We have found 9 complementation groups by means of the cross streak method applied in an incubator which maintains a constant non‐permissive temperature. The same method permits the rapid recognition of ts mutations in previously defined genes immediately after mutagenesis.
Reduction of cycloalkanones by several microorganisms
Authors: Lemière G. L. , van De Wal A. J. , Geens B. C. , Pattijn V. G. , Alderweireldt F. C. , Voets J. P. 
Published: July 2010

AbstractInvestigations were carried out on the reductive capacity of several microorganisms growing in the presence of decalones and monocyclic ketones. Some microorganisms (2 mould strains and 11 bacterial strains) were isolated from the soil, while others (8 mould strains) were obtained from type culture collections.The reductive capacities of these strains towards several cyclic ketones, such as cyclopentanone, ‐hexanone, and ‐heptanone and the respective 2‐substituted derivatives were studied. In view of further investigations on the mechanism of these reductions, standard procedures (inoculation, incubation, etc.) have been elaborated in order to allow quantitative comparison of the results.
Kinetik des Wachstums und der Riboflavinüberproduktion von Candida guilliermondii in kontinuierlicher Kultur
Authors: Sauerstein J. , Straube G. , Fritsche W. 
Published: July 2010

AbstractThe kinetics of growth, yield, and riboflavin overproduction in continuous culture of Candida guilliermondii were investigated. Iron was the limiting substrate with an influent concentration of 10 μg Fe μ 1−1.The steady state concentration of biomass increases with decreasing dilution rate (D) in the range of D between 0.019 and 0.184 h−1.The production of biomass per glucose (YC6H12O6) decreases from 0.260 to 0.093 with decreasing dilution rate from 0.184 to 0.019 h−1. Under conditions of 0 < D ≦ 0.012 h−1 the growth is not only limited by substrate iron.The steady state riboflavin concentration increases with decreasing D, if 0.019 ≦ D ≦ 0.136 h−1. The quotient p̄RF/√x demonstrating the amount of produced riboflavin per biomass also increases. Maximum values of specific riboflavin formation rate (kpRF) are measured at dilution rates about 0.136 h−1.It is concluded that growth and riboflavin overproduction are connected.
De novo‐Biosynthese von Nikotinsäure bei Candida lipolytica
Authors: Böttcher F. , König A. , Samsonova I. A. , Birnbaum D. , Lutzmann H. 
Published: July 2010

AbstractMNNG‐induzierte Mutanten mit einer blockierten Nikotinsäurebiosynthese wurden bei einem imperfekten und einem zur sexuellen Vermehrung befähigten Stamm von C. lipolytica isoliert und phänotypisch charakterisiert. Es konnten Mutanten mit einer inaktiven Tryptophanpyrrolase (nic1), Kynureninhydroxylase (nic2), 3‐Hydroxykynureninase (nic3) und einer blockierten Synthese von Nikotinsäure aus 3‐Hydroxyanthranilsäure (nic4) erhalten werden.Mit Hilfe der Mutanten wurde festgestellt, daß in beiden C. lipolytica‐Stämmen die Nikotinsäure nur ein Folgeprodukt des Tryptophanabbaus über Formylkynurenin, Kynurenin, 3‐Hydroxykynurenin und 3‐Hydroxyanthranilsäure ist. Der Kurzschluß‐ sowie der Bakterienweg der Nikotinsäurebiosynthese können auch nicht bei Anthranilsäure‐ oder Glycerinfütterung bzw. unter Bedingungen, die Katabolitrepression ausschließen, realisiert werden. In dieser Hinsicht unterscheidet sich C. lipolytica von den anderen bisher untersuchten Hefen.Eine Regulation des Tryptophan‐Nikotinsäure‐Weges durch Endprodukthemmung scheint nicht vorzuliegen.
Effect of mineral acids on iron bacteria
Authors: Barbić F. F. , Bracilović D. M. 
Published: July 2010

AbstractThe oxidative ability of Thiobacillus ferrooxidans in the presence of different concentrations of H2SO4, HCl, HNO3, and their mixtures was investigated. Bacteriological oxidation of FeSO4 is expressed as a function of time and acid concentration. For each acid and for their mixtures lethal concentrations for T. ferrooxidans were found experimentally. On the basis of the lethal concentration for each acid separately the lethal concentrations of their mixtures were computed and it was found that they are in good agreement with the experimental data.
Photobiological behaviour of bacteria and phages supplemented with aza‐analogues of nucleic acid bases
Authors: Kittler L. , Hradečna Z. , Jacob H.‐E. , Löber G. 
Published: July 2010

AbstractThe photochemical stability of anomalous nucleic acid bases of the azatype, 5‐azacytosine (I), 5‐azacytidine (II), 6‐azacytosine (III), 6‐azacytidine (IV), 6‐azathymine (V), 6‐azauracil (VI), and 8‐aza‐adenine (VII) to U. V. light of the wavelength 254 nm differs from the U. V. stability of the normal constituents. Changes of the U. V. inactivation ofEscherichia coliK12 C600,E. coliB,Bacillus cereus, as well asE. coliphages λ cb2and λ b2b5supplemented with azaderivatives prior to irradiation were investigated. It was found that I, II, III, IV, and VII are more, V and VI less sensitive to U. V. light compared with corresponding natural nucleic acid bases. Their changed U. V. sensitivities are reflected in the survival curves after U. V.‐irradiation in as far as azabases are incorporated into the nucleic acidsin vivo.This explains the increase in U. V. sensitivity ofE. coliK12 C600,E. coliB, andB. cereussupplemented with I, II, III, IV, and VII and the decrease in U. V. sensitivity ofStreptococcus faecalissupplemented with V (the latter information was taken from GÜNTHER and PRUSOFF 1967). The lack of any significant influence on inactivation curves ofE. coliK12 C600 by V and VI, and onE. coliphages λ cb2and λ c2b5by II, is discussed in terms of too small incorporation rates. No discrimination was put forward with respect to DNA and RNA incorporation.
Abhängigkeit der Ausbildung bestimmter Antigene von Proteus mirabilis Stamm 1095/67 beim Wachstum auf Minimalnährmedien
Authors: Reissbrodt R. , Kemmer G. , Seltmann G. 
Published: July 2010

AbstractProteus mirabilis strain 1095/67 has been cultivated in surface culture on different minimal media, which were composed either of single amino acids or combinations of several amino acids without or with stepwise addition of other C‐sources up to the complete medium. We found a direct dependence of the formation of the various antigens (moving to the cathode, to the anode, or not moving) on the composition of the medium.Certain amino acids (Ala, Glu, Asp, Ser) elicit only parts of the antigenic spectrum formed in complete medium, but enrich special antigens. With only 2 amino acids (Ala and Glu) and the vitamins thiamine, pyridoxal, and niacine in the anorganic basic medium the complete antigenic spectrum can be formed. We have shown that the composition of the cell wall varies with the composition of the culture medium.In shaked cultures we found serine to be essential for the production of the antigen moving to the cathode and the thermolabile antigene moving to the anode (ATA), niacine to be of fundamental importance in the biosynthesis of all antigens. Already under very limited supply of nutrients ATA, common to all gram‐negative bacteria, is formed and, therefore, it seems to be a very basic cell wall component.
Amylase of the thermophilic actinomycete Thermomonospora vulgaris
Authors: Allam A. M. , Hussein A. M. , Ragab A. M. 
Published: July 2010

Abstractα‐Amylase of the thermophilic actinomycete Thermomonospora vulgaris was partially purified. Maximal enzyme activity was obtained at 60 °C and pH 6.0. KM value was 1.4%. The effect of some metal salts on enzyme activity was studied. Enzyme activity was inhibited by KCN, EDTA, and iodoacetate. Inhibition by EDTA was completely nullified by CaCl2, but the inhibition by iodoacetate was not overcome by 2‐mercaptoethanol. Exposure of the enzyme to pH 7.0 and 9.0 for 2hr. did not affect the enzyme, but exposure to pH 3.0 for few minutes completely inactivated the enzyme. Exposure of the enzyme to 60 °C resulted in an appreciable inactivation and exposure to 80 °C completely inactivated the enzyme. Addition of CaCl2, 2‐mercaptoethanol, or enzyme substrate did not stabilize the 60 °C exposed enzyme. However, bovine serum albumin had a protective effect when the enzyme was exposed to 60 °C but not to 80 °C. The enzyme was stable in the presence of 8 M urea.
Effects of the antibiotic resistomycin on the synthesis of macromolecules
Authors: Haupt I. , Wähnert U. , Pitra Ch. , Löber G. , Luck G. , Eckardt K. 
Published: July 2010

AbstractResistomycin preferentially inhibits RNA synthesis in comparison to DNA and protein synthesis in intact bacterial cells. Studies with cell‐free systems have shown that the antibiotic interferes with DNA and RNA synthesis, while protein synthesis is inhibited to a much lesser extent. Detailed studies in cell‐free systems indicate an interaction of resistomycin with DNA‐ and RNA polymerase. In the case of RNA polymerase this was proved by CD measurements, whereas no interaction of the antibiotic with DNA, RNA, and homopolynucleotides could be found. One can conclude that the binding of the antibiotic to RNA polymerase is the basis for its interference with RNA synthesis.
Physiologie und Biochemie der Streptomyceten. III. Einbau von D‐Glucose‐u‐14C in Paromomycin als Indikator für die Antibioticabildung durch Streptomyces albus var. metamycinus nov. var.
Authors: Köster H. , Liebermann B. , Reuter G. 
Published: July 2010

AbstractParomomycin was isolated from culture filtrates of Streptomyces albus var. metamycinus nov. var. after feeding the growing cultures with D‐glucose‐u‐14C. From the different incorporation rates conclusions concerning different features of the paromomycin biosynthesis (utilization of the carbon source, proportional and disproportional changes of the rates of synthesis) could be drawn. Uptake and metabolism of glucose are discussed.
Pyridinnucleotid‐unabhängige Oxydation von längerkettigen aliphatischen Alkoholen durch ein Enzym aus Acinetobacter calcoaceticus
Authors: Tauchert H. , Roy M. , Schöpp W. , Aurich H. 
Published: July 2010

AbstractBei A. calcoaceticus 69‐V wird nach Ultraschallaufschluß im zellfreien Rohextrakt ein Pyridin‐nucleotid‐unabhängiges Enzym zur Oxydation von längerkettigen primären aliphatischen Alkoholen nachgewiesen. Als Testsubstrate wurden Hexanol und Octanol verwendet. Als Elektronen‐akzeptor kann Dichlorphenolindophenol dienen. Der entstehende Aldehyd wird als Phenyl‐hydrazon identifiziert und quantitativ gemessen. DCIP‐Abnahme und Hydrazonzunahme ent‐sprechen sich. Das pH‐Optimum der Reaktion liegt bei 7,5. Phenazinmethosulfat hat keinen Einfluß auf die Reaktionsgeschwindigkeit. Die spezifische Aktivität des Enzyms liegt nach Wachstum auf n‐Alkanen etwa bei 4 nMol/min/mg Protein; nach Wachstum auf Äthanol ist das Enzym nicht nachweisbar.
Induzierbare Akkumulation von α‐Ketoglutarsäure in Kulturen eines Makrolidantibioticum‐bildenden Stammes von Streptomyces hygroscopicus JA 6599
Authors: Gräfe U. , Bocker H. , Reinhardt G. , Thrum H. 
Published: July 2010

AbstractThe excessive production of pyruvic and 2‐oxoglutaric acid by S. hygroscopicus JA 6599 grown on a medium rich in complex carbon and nitrogen sources was studied.Towards the end of the first day of batch cultivation a maximum level of both keto acids in the medium was observed. By diluting the complete culture with water at 22nd hour, however, a further increase of 2‐oxoglutarate concentration was induced and the antibiotic production was slightly stimulated. In diluted cultures the oxygen saturation was found to be distinctly higher than in non‐diluted ones and, on the other hand, the mycelial activities of both pyruvate and 2‐oxoglutarate decarboxylases were decreased.Since the 2‐oxoglutarate level was strongly influenced by inhibitors of glycolysis and of citric acid cycle, it is suggested that the metabolite accumulation in diluted cultures is mainly caused by modifications of the metabolic control of carbohydrate catabolism due to an improved aeration. Furthermore, the macrolide antibiotic A 6599 produced by S. hygroscopicus JA 6599 itself was shown to interfere with the accumulation of 2‐oxoglutaric acid.
Regulation der Aktivität des Malatenzyms aus Acinetobacter durch organische Säuren
Authors: Kleber H.‐P. , Aurich H. 
Published: July 2010

AbstractDer Einfluß von organischen Säuren des Citrat‐ und Glyoxylatzyklus sowie einiger Aminosäuren auf die Aktivität des Malatenzyms aus Acinetobacter calcoaceticus wird untersucht. Von den eingesetzten Verbindungen hemmen nur Oxalacetat und Glyoxylat das Enzym deutlich.Oxalacetat ergibt mit L‐Malat als dem variablen Substrat in der doppelt‐reziproken Darstellung einen nicht‐linearen Kurvenverlauf. Die Hemmung ist vom pH‐Wert abhängig. Mit NADP+ als dem variablen Substrat zeigt Oxalacetat eine nicht‐kompetitive Hemmung.Glyoxylat hemmt das Malatenzym gegen L‐Malat kompetitiv linear (KI = 1,7 × 10−4 M). Die Hemmung ist vom pH‐Wert unabhängig. Mit NADP+ als dem variablen Substrat wird eine gemischte Hemmung erhalten, wobei Vmax stärker beeinflußt wird als der scheinbare KM‐Wert.
Bacterial leaching of waste uranium materials
Authors: Barbič F. F. , Bracilović D. M. , Krajinčanić B. V. , Lučić J. L. 
Published: July 2010

AbstractThe effect of ferrobacteria and thiobacteria on the leaching of waste uranium materials from which 70–80% of uranium was previously leached by classical chemical hydrometallurgical procedure has been investigated. The bacteria used are found in the ore and the mine water of Zletovska River locality, Yugoslavia. Parameters of biological leaching were examined in the laboratory. Leaching conditions were changed with the aim of increasing the amount of uranium leached. The effect of pyrite added to the waste materials before the beginning of leaching has also been examined. Uranium leaching is directly proportional to the composition and number of ferrobacteria and thiobacteria, and increased by almost twice the value obtained from the same starting materials without using bacteria.Increased sulphuric acid concentrations stimulate considerably the rate of leaching. Uranium leaching is increased up to 20% while sulphuric acid consumption is simultaneously decreased by the addition of pyrite.Uranium concentrations in starting waste materials used for leaching were extremely low (0.0278 and 0.0372% U) but about 60% recovery of uranium was obtained, with relatively low consumption of sulphuric acid.
Proteinkristalle und Tubuli‐Bündel in Hefezellen III. Identifizierung der Kristalle als Alkoholdehydrogenase (ADH)
Authors: Künkel W. 
Published: July 2010

AbstractInducibility of alcohol dehydrogenase (ADH) crystals in yeast cells depends on the growth phase. They accumulate during exponential growth, a process that is parallelled by accumulation of a special protein (H protein). The following pieces of evidence show that crystals, H protein, and ADH are identical:
The three proteins have the same amino acid composition and subunit molecular weight;
active H protein and ADH exhibit the same electrophoretic mobility, indicating a common molecular weight of about 158000 D;
the native H protein and a crystal fraction stabilized by Zn++ and dialyzed against EDTA possess ADH activity.
Einfluß unterschiedlicher Temperaturen auf Stoffwechsel, Phagozytosevermögen und Vitalität von Tetrahymena pyriformis
Authors: Burmeister J. 
Published: July 2010

AbstractDer Stoffwechsel, das Phagozytosevermögen und die Vitalität von Tetrahymena pyriformis HS wurden in ihrer Abhängigkeit von der Temperatur in einem Bereich von 10°C—42,5°C untersucht. Zwischen 15 °C und 35 °C steigt die Atmung linear mit der Temperatur an. Die Temperaturkoeffizienten Q10 sind entsprechend im Bereich von 10 °C—15 °C sehr hoch: 4,1; zwischen 15 °C und 25 °C betragen sie 2,6 und zwischen 25 °C und 35 °C 1,6. Bei 40 °C nimmt die Atmung stark ab, aber auch bei der letalen Temperatur von 42,5 °C ist noch ein gewisser O2‐Verbrauch zu registrieren. Ein durch Phagozytose atmungsaktiver Substanzen gesteigerter Stoffwechsel zeigt relativ die gleiche Reaktion auf Temperaturerhöhung und gleiche Werte für den Stoffwechsel‐koeffizienten wie der Ruhestoffwechsel, es dürfte sich danach um ein und dasselbe Stoffwechselsystem handeln. Das Phagozytosevermögen setzt oberhalb 10 °C ein und hat ein Optimum zwischen 25 °C und 35 °C, bei 40 °C erfolgt schon eine starke Einschränkung. Eine strenge Parallelität zur Höhe des Stoffwechsels kann nicht festgestellt werden, die geringe Steigerung zwischen 25 °C und 35 °C dürfte durch physikalische Prozesse bedingt sein. Bei der Phagozytose können deutlich 2 Anteile unterschieden werden: Phagozytosegrad und Phagozytoseindex, beide werden durch die Temperatur gleichsinnig beeinflußt. Der Cilienschlag ist bei 5 °C noch nicht erloschen, wenn auch stark verlangsamt, er hört erst beim Erreichen der oberen Vitalitätsgrenze (42,5 °C) auf. Von den untersuchten Zellfunktionen ist das Phagozytosevermögen empfindlicher als der Cilienschlag und das Ausschließungsvermögen für Trypanblau. Bei einem Vergleich mit anderen Phagozyten, den Leukozyten (PML) der Säugetiere ergeben sich folgende Unterschiede: Ihre Tempera‐turtoleranz ist größer, speziell auch die des Phagozytosevermögens, dagegen ist ihre Zellbeweglichkeit (Migration) empfindlicher gegenüber Hyperthermie. Bei beiden Objekten konnte noch ein geringer Sauerstoffverbrauch auch nach dem Überschreiten der oberen Vitalitätsgrenze festgestellt werden. Schließlich sei noch einmal auf den unterschiedlichen Grundstoffwechsel beider Zellarten — Tetrahymena oxydativ, Leukozyten glykolytisch—verwiesen. Der gesteigerte Sauerstoffverbrauch während der Phagozytose, der bei Tetrahymena auf einer Steigerung des Grundstoffwechsels beruht, wird bei den Leukozyten durch die Aktivierung eines neuen Stoffwechselsystems (Pentosephosphatzyklus) hervorgerufen.
Mutagenesis in bacteriophage T 7. I. Chemically induced mutagenesis
Authors: Meyer M. 
Published: July 2010

AbstractThe mutagenesis in phage T 7 after MMS‐, HNO2‐, hydroxylamine‐, 5‐BUdR‐, and 2‐AP‐treatment in relation to host controlled functions is investigated. There was no dependence of the induction of mutations on the character of the host strains (rec, hcr). A back mutation system (amber system) and a forward mutation system (host range system) have been used. Substances which cause mainly transitions from GC to AT do not lead or only rarely lead to reversions of the amber system; but chemicals producing transitions from AT to GC do so.