The sensitivity of halobacteria to antibiotics

Abstract Eleven species of the genera Halobacterium, Halococcus and the recently proposed Haloarcula were tested by the macro-broth dilution method for their sensitivity to 20 antibiotics with different modes of action. The most active were bacitracin, erythromycin, haloquinone, rifampicin and novobiocin. Resistant mutants of H. mediterranei to bacitracin, chloramphenicol and josamycin were obtained with frequencies of spontaneous mutation between 10⁻⁴ and 10⁻⁷.     

Mitochondrial mutagenesis in Saccharomyces cerevisiae. III. Nitrous acid.

Nitrous acid (NA) induced mutations efficiently in mitDNA, conferring resistance to erythromycin and weakly induces mit- mutations. In some strains of yeast it also enhanced rho- mutations. The frequencies of nuclear and mitochondrial mutations induced with NA are compared.     

Novel shuttle plasmid vehicles for Escherichia-Streptococcus transgeneric cloning

A novel plasmid vector that is able to replicate both in Escherichia coli and in Streptococcus sanguis is described. This 9.2-kb plasmid, designated pVA856, carries Cm^r, Tc^r and Em^r determinants that are expressed in E. coli. Only the Em^r determinant is expressed in S. sanguis. Both the Cm^r and the Tc^r of pVA856 may be insertionally inactivated. This plasmid affords several different cleavage-ligation strategies for cloning in E. coli followed by subsequent introduction of chimeras in to S. sanguis. In addition, we have modified a previously described E. coli-S. sanguis shuttle plasmid [pVA838; Macrina et al., Gene 19 (1982) 345–353], so that it is unable to replicate in S. sanguis. The utility of such a plasmid for cloning and selecting sequences enabling autonomous replication in S. sanguis is demonstrated.     

Resistance in tomato to the greenhouse whitefly: analysis of population dynamics

Life history parameters including longevity, developmental time, and reproduction were determined for whiteflies, Trialeurodes vaporariorum (Westwood), kept in clip-on cages on susceptible parent, Lycopersicon esculentum, resistant parent, L. hirsutum glabratum, and intermediate breeding lines of tomato. Using the Lewontin triangular reproductive function, the intrinsic rate of increase (r_m) was calculated for each genotype. This is an elegant tool for detecting resistance, as it incorporates all salient factors of life history. Comparing r_m to the other parameters measured, selection criteria were chosen. Developmental time is not a suitable selection criterion as it varies very little even between the most susceptible and the most resistant genotypes. Additionally, developmental time of T. vaporariorum offspring was found to be highly significantly correlated to parental age on all tomato genotypes except L. hirsutum glabratum. Total reproduction, truncated population counts, and longevity appear good criteria for selection. This test, focusing on antibiotic factors, shows large differences between the resistant and susceptible parent genotypes, but much smaller differences between the breeding lines and the susceptible parent. Earlier screenings relying on a variety of tests appear to have maintained antixenotic rather than antibiotic properties in the breeding lines.     

Preferred ambient temperature for old and young men in summer and winter

To investigate the effects of age on thermal sensitivity, preferred ambient temperature (T _pref) was compared between old (71–76 years) and young (21–30 years) groups, each consisting of six male subjects in summer and winter. The air temperature (T _a) was set at either 20° C or 40° C at commencement. The subject was directed to adjust theT _a for 45 min by manipulating a remote control switch to the level at which he felt most comfortable. In the older group, theT _pref was significantly lower in trials starting at 20° C than that starting at 40° C in summer. The fluctuation ofT _pref (temperature difference between maximum and minimumT _a during the last 10 min) was significantly wider in the older group in both summer and winter. Repetition of the same experiment on each subject showed a poorer reproducibility ofT _pref in the older group than in the younger group in summer. Tympanic and esophageal temperatures of the older group kept falling throughout the trial starting at 20° C in summer. These results suggest that thermal sensitivity is decreased with advancing age and that thermal perception in the elderly, especially to cold, is less sensitive in summer.     

Agrobacterium rhizogenes mediated induction of apparently untransformed roots and callus in chrysanthemum

The agropine type Agrobacterium rhizogenes strain LBA9402 induced callus and roots on stems of greenhouse grown plants and on leaf disks of in vitro grown plantlets of chrysanthemum (Dendranthema grandiflora Tzvel.). In this callus and roots no opines were detected, nor were any of the other features of the hairy root syndrome observed. Experiments aimed to identify the nature of the tumour-like growth revealed that induction was correlated with the presence of the TR-DNA on the Ri-plasmid. Root induction was probably the result of auxin synthesis following transient expression of iaaM and iaaH genes, present on the TR-DNA. The chrysanthemum cultivar used, cv. Parliament, showed a high auxin sensitivity compared to tobacco. Analysis of early transformation events using the GUSintron reporter gene revealed that low efficiency gene transfer and transient gene expression took place, but most probably without stable integration of the T-DNA in the plant genome. The results presented here stress the fact that callus formation or root induction as measures for transformation efficiency should be used with caution.     

Cloning and characterization of a plasmid DNA from anacystis nidulans 6301

A plasmid DNA of Anacystis nidulans 6301 was isolated by CsCl-EtBr centrifugation. The Mr of the plasmid, named pBA1, was estimated to be 5.04 +/- 0.26 X 10(6) by electron microscopic analysis and 5.2 X 10(6) by agarose gel electrophoresis. The pBA1 DNA was opened at a unique site with BamHI and cloned in pBR322 vector propagated in Escherichia coli HB101 cells. The recombinant plasmid, named pBAS18, was digested with various restriction endonucleases and its cleavage map was constructed. Based on this result, the cleavage map of the pBA1 plasmid is presented.     

Valine resistant plants derived from mutated haploid and diploid protoplasts of Nicotiana sylvestris and N. tabacum

Summary Protoplasts were derived from haploid and diploid Nicotiana sylvestris and N. tabacum. Exposure of the protoplasts to mutagenic doses of ultraviolet (U.V.) radiation prior to two selection rounds in the presence of 4 mM (or 5 mM) and 8 mM of valine, respectively, was required to obtain cell lines with persistent valine resistance. Such lines were obtained from haploid and diploid N. sylvestris protoplasts as well as from haploid protoplasts of N. tabacum but not from (1.8 × 10⁷) diploid N. tabacum protoplasts. The ratio between number of verified valine-resistant cell lines and the initial number of U.V. exposed protoplasts enabled the estimation of the following order of mutation frequency: haploid N. sylvestris > haploid N. tabacum > diploid N. sylvestris. Plants which retained the valine resistance and transmitted it to their sexual progeny were derived from the resistant cell lines.     

The effect of cessation of growth on protein synthesis in a mutant of Chinese hamster ovary cells with a temperature-sensitive leucyl-tRNA synthetase

A temperature-sensitive mutant of Chinese hamster ovary cells with an altered leucyl-tRNA synthetase fails to grow and to incorporate amino acids into protein properly at or near the non-permissive temperature. This mutant was used to determine whether cessation of growth at the elevated temperature affected elongation factor EF-1, since the activity of EF-1 is markedly lower in non-growing cells in stationary phase than in rapidly-growing cells in exponential phase. Cell-free extracts prepared from cells maintained at 39°C for 24 h showed a marked decrease in the ability to translate natural mRNAs, compared to cells incubated at 34°C. However, the ability to translate poly(U), which requires elongation factor EF-1 (and EF-2), was not affected. Analyses of activities involved in the initiation of protein synthesis and in the activation of amino acids revealed that, with the exception of leucyl-tRNA synthetase, the rest of the components required for translation also appeared to be relatively stable even after 24 h at the elevated temperature. The effects of elevated temperature on cell-free extracts were also investigated. The results were similar to those obtained with intact cells; that is, except for leucyl-tRNA synthetase which was rapidly inactivated in vitro at 39°C, other aminoacyl-tRNA synthetases and translational components involved in chain initiation and elongation were relatively stable. Thus, no change in EF-1 activity was detected as a result of arrested cell growth, an inherent lability of the elongation factor, or metabolic degradation as a consequence of a rapid turnover rate in the absence of protein synthesis.