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1.
Isolation and characterization of pyridoxine auxotrophs of Escherichia coli   总被引:6,自引:5,他引:1  
Dempsey, Walter B. (University of Florida, Gainesville), and P. F. Pachler. Isolation and characterization of pyridoxine auxotrophs of Escherichia coli. J. Bacteriol. 91:642-645. 1966.-Pyridoxine auxotrophs of Escherichia coli B have been consistently produced by a modified penicillin enrichment method. This modified penicillin technique included a 6-hr growth period in the absence of any pyridoxine followed by a 2-hr treatment with penicillin at 1,000 units per ml. Penicillin was removed from these cultures by membrane filtration and the process was repeated. A minimum of three cycles was found necessary to isolate auxotrophs. Different phenotypes within the group of pyridoxine auxotrophs were distinguished by their responses to feeding with the various forms of pyridoxine, as well as by cross-feeding tests. Two auxotrophs were also differentiated by their frequency of reversion to prototrophy. Cross-feeding tests indicated that seven of the phenotypes fed in a linear sequence. These phenotypes had a very low frequency of reversion. The auxotrophs with a high frequency of reversion cross-fed in a linear sequence and fed the first five of the other seven auxotrophs. One of the auxotrophs isolated was a pyridoxal auxotroph.  相似文献   

2.
Twenty one cysteine and 13 methionine auxotrophs of Sinorhizobium meliloti Rmd201 were obtained by random mutagenesis with transposon Tn5. The cysteine auxotrophs were sulfite reductase mutants and each of these auxotrophs had a mutation in cysI/cysJ gene. The methionine auxotrophs were metA/metZ, metE and metF mutants. One hundred per cent co-transfer of Tn5-induced kanamycin resistance and auxotrophy from each Tn5-induced auxotrophic mutant indicated that each mutant cell most likely had a single Tn5 insertion. However, the presence of more than one Tn5 insertions in the auxotrophs used in our study cannot be ruled out. All cysteine and methionine auxotrophs induced nodules on alfalfa plants. The nodules induced by cysteine auxotrophs were fully effective like those of the parental strain-induced nodules, whereas the nodules induced by methionine auxotrophs were completely ineffective. The supplementation of methionine to the plant nutrient medium completely restored symbiotic effectiveness to the methionine auxotrophs. These results indicated that the alfalfa host provides cysteine but not methionine to rhizobia during symbiosis. Histological studies showed that the defective symbiosis of methionine auxotrophs with alfalfa plants was due to reduced number of infected nodule cells and incomplete transformation of bacteroids.  相似文献   

3.
Micrococcus glutamicus ATCC 13032, a glutamic acid-producing organism, was treated with 0.2M ethylmethane sulfonate, the auxotrophs isolated showing varied patterns of extracellular amino acids. Eighty auxotrophic strains were obtained, out of which 31 excreted 1.0-4.0 mg threonine per ml and all the auxotrophs required biotin for growth and production of the amino acid. Eleven auxotrophs produced 1.5 to 3.0 mg alanine per ml and these auxotrophs required amino acids for their growth. Other auxotrophs lost their excretion capacity in subsequent fermentation trials. Further mutation of the biotin-requiring auxotroph Micrococcus glutamicus EM with gamma rays resulted in the isolation of 89 auxotrophic strains, out of which 28 excreted threonine (up to 5.0 mg per ml) higher than the parent auxotroph. Exposure to X-rays yielded 97 auxotrophs, out of these 35 producing 1.0-3.0 mg methionine per ml and requiring biotin for growth and production of the amino acid. Other auxotrophs produced alanine (0.5 to 2.0 mg per ml) and threonine (2.0 to 3.3 mg per ml). Irradiation with gamma rays favoured the development of threonine producing auxotrophs while X-rays favoured methionine-producing auxotrophs.  相似文献   

4.
To develop a biochemical genetic approach to understanding cell carbon synthesis or metabolic pathways in methanogens, Methanobacterium ivanovii was selected as a model organism for genetic manipulation studies. The organism displayed a colony size of 3 to 6 mm in less than 2 weeks and had a plating efficiency of about 90%, which made it suitable for replica plating. Mutagenesis and selection techniques were developed for selection of acetate auxotrophs. Chemical mutagenesis with ethyl methanesulfonate, followed by enrichment with bacitracin as a selective agent, resulted in stable acetate auxotrophs. M. ivanovii was very sensitive to UV, but UV-induced acetate auxotrophs were unstable and reverted within two to four transfers. The acetate auxotrophs were analyzed in relation to wild type for carbon monoxide dehydrogenase enzyme activity.  相似文献   

5.
Starvation survival response of Mycobacterium tuberculosis   总被引:3,自引:0,他引:3       下载免费PDF全文
Parish T 《Journal of bacteriology》2003,185(22):6702-6706
The ability of Mycobacterium tuberculosis auxotrophs to survive long-term starvation was measured. Tryptophan and histidine auxotrophs did not survive single-amino-acid starvation, whereas a proline auxotroph did. All three auxotrophs survived complete starvation. THP-1 cells were also able to restrict the growth of the tryptophan and histidine auxotrophs.  相似文献   

6.
Natural heterozygosity in Candida albicans.   总被引:24,自引:8,他引:16       下载免费PDF全文
We subjected 16 Candida albicans clinical isolates to ultraviolet radiation and tested the survivors for auxotrophy. Six isolates displayed strongly biased auxotroph spectra: three yielded methionine auxotrophs, two yielded both isoleucine-valine and adenine auxotrophs, and one yielded lysine auxotrophs. We present evidence that auxotrophs arise by segregation from naturally occurring heterozygous states. The remaining isolates yielded few or no auxotrophs in an arbitrary sample (greater than 2,500) of survivors of irradiation. Our experiments indicate that C. albicans is diploid, although aneuploidy (2n + i) cannot be rigorously excluded. We discuss the possible utility of heterozygosity as a marker in epidemiological studies, and we discuss a rationale for the frequent occurrence of heterozygosity.  相似文献   

7.
Summary A protocol has been developed for the negative selection of plant auxotrophs using the nucleoside analogues BUdR and FUdR. The protocol was optimised using nitrogen-starved protoplast-derived cells of Nicotiana plumbaginifolia to simulate auxotrophy. The present results represent a significant improvement over previous reports in that: 1) The background of colonies escaping BUdR/FUdR kill is low and reproducible. 2) The protocol was improved to the point where background survival was 0.03% for non-starved cultures and 0.09% for auxin-starved cultures. 3) It was shown that UV irradiation decreases BUdR sensitivity of dividing cells and that this is overcome by increased exposure to BUdR. 4) Application of the method to auxin-starved haploid protoplast-derived cell suspensions resulted, for the first time, in the selection of temperature-sensitive (ts) auxin auxotrophs. 5) It could be demonstrated, for the first time, that the method in practice enriches for auxotrophs, in this case by a factor of 10 for auxin auxotrophs and at least 60 for ts auxin auxotrophs.Abbreviations BUdR 5-bromodeoxyuridine - FUdR 5-fluoro-deoxyuridine - MNNG N-methyl-N-nitro-N-nitrosoguanidine - NAA 1-naphthaleneacetic acid - BAP 6-benzylamino-purine - CFE colony forming efficiency - PE plating efficiency - ts temperature sensitive  相似文献   

8.
Addition of certain ribonucleosides to exponentially growing cultures of Escherichia coli increased the extent of thymidine incorporation. The prolonged uptake of thymidine was correlative with the ability of these ribonucleosides to prevent the degradation of thymidine. In addition to protecting thymidine, uridine reversed partially (70 to 80%) the inhibition of deoxyribonucleic acid (DNA) synthesis in thymineless auxotrophs by cytosine arabinoside, hydroxyurea, and nalidixic acid. This reversal was selective for auxotrophic strains since no reversal of inhibition by uridine was observed in any of the prototrophic strains examined. In the presence of uridine, the rapid assimilation of thymidine by prototrophic and auxotrophic strains was prevented and the rate of DNA synthesis became a function of the available exogenous thymidine. Under these conditions, prototrophic strains accumulated equivalent amounts of thymidine into the acid-soluble (pool) and acid-insoluble (DNA) cell fractions. In contrast, 95 to 98% of the thymidine taken up by auxotrophs was found in the acid-insoluble (DNA) cell fraction. The results suggest that different mechanisms for DNA synthesis exist in auxotrophs and prototrophs. Based on these observed differences, some possible mechanisms for the selective reversal of the inhibition of DNA synthesis in auxotrophs are discussed.  相似文献   

9.
S Kondo  A Yamagishi    T Oshima 《Journal of bacteriology》1991,173(23):7698-7700
Uracil auxotrophs of Sulfolobus acidocaldarius were positively selected by using 5-fluoroorotic acid. The wild-type strain was unable to grow in medium containing 5-fluoroorotic acid, whereas the mutants grew normally. Positive selection could be done for the auxotrophs. Mutants deficient in orotidine-5'-monophosphate pyrophosphorylase activity were isolated.  相似文献   

10.
A protocol employing inositol starvation was used to isolate proline and adenine auxotrophs of Candida tropicalis. Interspecific hybrids between red adenine auxotrophs of C. tropicalis and Candida albicans were formed by protoplast fusion. These C. tropicalis red adenine auxotrophs were shown to fall into two complementation groups by crossing them with a known C. albicans ade1 tester strain. It is suggested that these two groups correspond to the ade1 and ade2 mutants of Saccharomyces cerevisiae and C. albicans and that these defined mutants may be useful in attempts to develop transformation systems for C. tropicalis.  相似文献   

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