Spontaneous and Induced Variations in Bacteria

Devi, Puliakote (1948) Spontaneous and Induced Variations in Bacteria. PhD thesis, University of Glasgow.

Abstract

Part I. Spontaneous and induced variations in bacteria Two different organisms, Bacterium prodigiosum and Bacterium aerogenes have been examined for Spontaneous variation. Individual colonies of these organisms were tested for their ability to grow in a simple, chemically defined medium in which the parent strain grows. Colonies which would not grow in this medium were taken to be of variant strains. Bact. aerogenes was employed for further work on induced variations or mutations as it gave a low rate of spontaneous variation. Mutations were induced by X-rays and were conducted first by irradiation of broth cultures and later of bacteria in the dry state. Production of mutations in dried bacteria has not been reported previously. Different methods of suspension of the bacteria for drying, and different methods of storage were explored. After irradiation the cultures were examined for mutant strains using the method of Lederberg and Tatum. A critical study of this method was undertaken. Two categories of mutants described as "adaptable", and "non-adaptable" were obtained. About 70% of the mutant strains were identified as unable to carry out the biosyntheses of certain amino-acids, vitamins, purines or pyrimidines. The rest grew only with the addition of yeast extract to the medium. Some of the strains were further studied by investigating their response to related substance or substances which might be intermediates in the biosynthesis of the supplement required. Part II. Studies on adaptations. Further studies have been conducted on the "adaptable" strains. Variations occurring in these strains were examined but no conclusion could be drawn as to whether this was due to natural selection or mutation. Adaptation of these strains in different adapting media in the presence or absence of cell multiplication were studied. The only tentative conclusion that could be drawn was that no adaptation occurred in v/ashed suspensions in the presence of a medium containing phosphate buffer and ammonium sulphate. Part III. The histidine-less and nicotinic-less mutants of Bact. aerogenes A10C, and the possibility of using them in microbiological assays. The suitability of the simple medium for the parent strain was first studied from the point of view of maximum growth and acid production and various modifications employed. Studies on the histidine-less and nicotinic-less mutants were then conducted by using the modified medium. The response of the histidine-less mutant (506, 297 and 9B2) to graded doses of histidine was found to be quantitative. The nicotinic-less mutants (893 and 3A3) responded to nicotinic acid in a peculiar way in that a "lag" in growth was found to occur at lower concentrations while no such "lag" occurred with nicotinamide. The effect of size of inoculum, the period of incubation, the H-ion concentration and the addition of a small amount of nicotinamide to the basal medium on the "lag" in growth at lower concentrations of nicotinic acid was then studied. Each of these factors were found to decrease the "lag" period completely or to a great extent.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Microbiology
• Date of Award: 1948
• Depositing User: Enlighten Team
• Unique ID: glathesis:1948-79691
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 04 Mar 2020 15:28
• Last Modified: 04 Mar 2020 15:28
• URI: https://theses.gla.ac.uk/id/eprint/79691