To elucidate the nature of bacterial assimilatory nitrate reductase, we attempted to use bacteria which contain assimilatory but not dissimilatory nitrate reductase. Four strains of bacteria (M-1, M-2, M-3 and J-1), isolated in this study, and Nocardia globerula IFO 13509 had such characteristics; they grew in a medium containing nitrate as the sole nitrogen source and did not accumulate nitrite, ammonia or molecular nitrogen during growth in nitrate synthetic or nitrate complex media with or without aeration. Strains M-1, M-2 and M-3 are Bacillus spp., which are either identical to or closely resemble B. megaterium, and strain J-1 is a Pseudomonas sp. which resembles P. hydrogenovora. Resting cells of these bacteria assimilated nitrate in the presence of glucose or pyruvate without accumulation of nitrite. Assimilatory nitrate reductase in cell-free extracts from the bacteria reduced nitrate if NADPH or NADH was added as an electron donor. Both NADPH and NADH served as the donor for the enzymes from M-1 and M-2, while only NADPH was the effective donor for the enzymes from M-3, J-1 and N. globerula. All the enzymes from these bacteria were predominantly localized in the soluble cytoplasmic fraction. Effects of inhibitors, such as KClO₃, NaN₃, NH₂OH and p-chloromercuri benzoate, were variable when one of the inhibitors was tested for the enzymes from different strains, but inhibition was similar when tested on the enzyme from the same strain (M-1 or M-2) with either NADPH or NADH. The enzymes from M-1, M-3 and J-1 were inhibited by 1mM KClO₃, but the enzymes from M-2 and N. globerula were not inhibited; the enzyme from M-2 was not inhibited by 1mM NaN₃, but the enzymes from the other strains were inhibited.

View full abstract

Flow microcalorimetry has been used to measure the anaerobic and aerobic rate of glucose catabolism by washed cell suspensions of Streptococcus agalactiae under flow and stopped flow conditions. The rate of glucose catabolism under aerobic and anaerobic conditions was similar, while heat production was greater under aerobic conditions due to divergence from a homolactic fermentation which was confirmed by enthalpy calculations. The pH of the buffer, in the range of 5.5 to 6.8, did not affect the rate of glucose catabolism or heat production. In the presence of 2, 4-dinitrophenol at a concentration optimized for maximum stimulation of glucose catabolism, the increased amount of glucose catabolized appeared as lactic acid under anaerobic and aerobic conditions; buffer pH determined the rate of glucose catabolism, with the maximum rate occurring at pH 6.0. The significance of pH in restricting the growth of different strains of lactic acid bacteria is considered in terms of the provision of energy from carbohydrate catabolism.

View full abstract

Three-factor crosses in both Rhizopus stolonifer and R. microsporus gave results which supported the hypothesis that normal sexual functions (karyogamy and meiosis) were operating in these species. However, not all meiotic products are recovered in the germsporangium of each germinating zygospore. When the number of germsporangia containing each genotype were scored, the sizes of the eight possible genotypes obtainable from a three-factor cross were found to be approximately equal. Likewise, allelic recovery values were approximately equal. Parental/recombinant figures indicate that none of the loci studied (3 in R. stolonifer and 4 in R. microsporus) were linked. Classification of each germsporangium according to the number and kinds of genotypes recovered revealed that 35% of those in R. stolonifer and 17% of those in R. microsporus contained products of more than one meiosis.

View full abstract

One of two 1.9kb HaeII segments of pSC101 is capable of autonomous replication. Replication of a plasmid containing the segment retains characteristics of the pSC101-type replication such as the dnaA-dependence, the copy number of the plasmid, the location of the origin, the direction of replication, and the incompatibility property. Analysis of deletion mutants revealed that a 1.65kb region within the HaeII segment contained functions sufficient for autonomous replication. A terminal 0.6kb segment on which the replication origin was mapped by an electron microscopic analysis of replicating molecules can replicate in the presence of a helper plasmid providing a traps-acting function and can express incompatibility toward pSC101.

View full abstract

This paper describes an evolutionary analysis of IS1 elements based on nucleotide sequence data from six iso-insertion elements of IS1 (iso-IS1s) which are present in chromosomes and plasmids of Escherichia coli and Shigella species as repeated sequences. The sequence comparison, which permitted construction of a phenogram, showed that the iso-IS1s can be divided into three groups. One group consists of four elements with 1% nucleotide sequence divergence. A second and third group each consists of one element, with 10% and 46% divergence, respectively, to the first group. Despite their divergence, amino acid sequences in the two IS1 encoded genes, insA and insB, and the terminal inverted repeat sequences, insL and insR, were found to be highly conserved. The evolutionary distance per site in the six sequences suggests that the IS1 element has diverged to a greater degree than bacterial genes of known nucleotide sequences have. We postulate that the existence of a group of well conserved iso-IS1s and of highly diverged iso-IS1s may be due to the transposition ability of the IS1 element, generating repetitive sequences in both bacterial chromosomes and plasmids which can then independently diverge. We also discuss possible regulatory mechanisms of transposition mediated by IS1 based on this analysis, including the influence of colon usage of insA and insB. The observed colon selection agrees well with those colons used by weakly expressed E. coli proteins.

View full abstract

Two new species of the genus Kitasatosporia are described, for which the names Kitasatosporia phosalacinea and Kitasatosporia griseola are proposed. The former produces a new peptide antibiotic, phosalacine, and the latter produces a known antibiotic, setamycin. As in K. setalba, the type species of Kitasatosporia, the aerial and submerged spores of two the new strains contain LL-2, 6-diaminopimelic acid (A₂pm), while the vegetative and filamentous mycelia contain meso-A₂pm. The type strain of K. phosalacinea is strain KA-338 (IFO 14372, JCM 3340) and that of K. griseola is strain AM-9660 (IFO 14371, JCM 3339).

View full abstract

An accumulator model for microorganisms is proposed to describe the mechanism generating the electron flow from microbes. This model is based on the following central assumption: the microbial cell surface has a function to charge electrons released from inside the organism and to discharge them to the outside. Escherichia coli was used to test this model. The model was very useful in analyzing the time course of the current generated by the organism. To determine the suitability of the model, the consistency between the predictions based on the model and the observations was investigated by the following two types of experiments. (1) An experiment to increase the rate of electron charge from the respiratory chain of E. coli to the cell surface by adding succinic acid to the cell suspension. (2) An experiment to increase the rate of electron discharge from the cell surface to the outside by adding an anion exchange resin to the cell suspension. In both experiments the predictions and the observations were in good agreement. Consequently it was concluded that the accumulator model is useful in understanding the electrical characteristics of microbes. It was confirmed that an anion exchange resin can cause an electron transfer from the E. coli to the resin owing to an attractive force between the electron on the cell surface and the positive charge on the surface of the resin. A cation exchange resin, having a negatively charged surface, and an electrically neutral resin had little effect on the current.

View full abstract