Genetic analysis of mutagenesis in aging Escherichia coli colonies

Bacteria live in unstructured and structured environments, experiencing feast and famine lifestyles. Bacterial colonies can be viewed as model structured environments. SOS induction and mutagenesis have been observed in aging Escherichia coli colonies, in the absence of exogenous sources of DNA damage. This cAMP-dependent mutagenesis occurring in Resting Organisms in a Structured Environment (ROSE) is unaffected by a umuC mutation and therefore differs from both targeted UV mutagenesis and recA730 (SOS constitutive) untargeted mutagenesis. As a recB mutation has only a minor effect on ROSE mutagenesis it also differs from both adaptive reversion of the lacI33 allele and from iSDR (inducible Stable DNA Replication) mutagenesis. Besides its recA and lexA dependence, ROSE mutagenesis is also uvrB and polA dependent. These genetic requirements are reminiscent of the untargeted mutagenesis in λ phage observed when unirradiated λ infects UV-irradiated E. coli. These mutations, which are not observed in aging liquid cultures, accumulate linearly with the age of the colonies. ROSE mutagenesis might offer a good model for bacterial mutagenesis in structured environments such as biofilms and for mutagenesis of quiescent eukaryotic cells. Received: 30 April 1997 / Accepted: 1 July 1997     

Expression of heterologous phytochromes A, B or C in transgenic tobacco plants alters vegetative development and flowering time

In this study, oat phytochrome A (phyA), Arabidopsis phytochrome B (phyB) or Arabidopsis phytochrome C (phyC) were expressed in both day-neutral and photo-period-sensitive (short-day) tobacco (Nicotiana tabacum cv. Hicks). Introgression of the Maryland Mammoth (MM) gene into cv Hicks was used to confer short-day photo-periodic sensitivity. Expression of oat phyA led to characteristic hypersensitivity of hypocotyls to red light (R) and far-red light (FR) and an overall dwarfing of the mature plant. Expression of Arabidopsis phyB enhanced the sensitivity of hypocotyls to R and caused even more marked dwarfing of the mature plant. In contrast, the expression of Arabidopsis phyC had no detectable consequences for the photocontrol of hypocotyl elongation. However, phyC expression did lead to a R-dependent increase in cotyledon expansion in de-etiolating seedlings and to a significant increase in leaf area in mature plants. This provides the first experimental evidence that phyC is biologically active. The flowering time of cv Hicks plants grown under 8 h photoperiods was virtually unaffected by a 30 min white light (W) night break given 8 h into the dark period. In contrast, cv Hicks MM plants responded to a night break with a delay in flowering. Expression of phyA or phyB led to a night break-dependent delay in flowering in cv Hicks plants. For cv Hicks MM plants, the expression of any of phyA, phyB or phyC caused a marked enhancement of the flower-delaying effect of a night break. These observations indicate that transgenic phyA, phyB or phyC can interact with the endogenous mechanisms controlling flowering time in tobacco.     

Suitability of oven-dried root nodules for Rhizobium strain identification by immunofluorescence and agglutination

Legume root-nodules, dried at oven temperature (70°C for 48 h) were suitable for Rhizobium strain identification by immunofluorescence and agglutination. The fluorescence of bacteroids of R. japonicum, R. leguminosarum, R. meliloti, R. phaseoli , and Rhizobium spp. from oven-dried nodules was the same as those from frozen, desiccated, or nodules dried at room temperature (28°C). Oven-dried nodules did not require further steaming for agglutination. Bacteroid agglutinations gave 2–16 fold lower titres than those of the cultured cells. Fresh and oven-dried soybean rhizobia from a mixed inoculation gave exactly the same results when identified by immunofluorescence or agglutination.     

Nucleotide sequence analysis of the lemur beta-globin gene family: evidence for major rate fluctuations in globin polypeptide evolution

Lemur beta-related globin genes have been isolated and sequenced. Orthology of prosimian and human epsilon-, gamma-, and beta-related globin genes was established by dot-matrix analysis. All of these lemur globin genes potentially encode functional beta-related globin polypeptides, though precisely when the gamma-globin gene is expressed remains unknown. The organization of the 18-kb brown lemur beta-globin gene cluster (5' epsilon-gamma-[psi eta-delta]-beta 3') is consistent with its evolution by contraction via unequal crossing-over from the putative ancestral mammalian beta-globin gene cluster (5' epsilon-gamma- eta-delta-beta 3'). The dwarf lemur nonadult globin genes are arranged as in the brown lemur. Similar levels of synonymous (silent) nucleotide substitutions and noncoding DNA sequence differences have accumulated between species in all of these genes, suggesting a uniform rate of noncoding DNA divergence throughout primate beta-globin gene clusters. These differences are comparable with those observed in the nonfunctional psi eta pseudogene and have therefore accumulated at the presumably maximal neutral rate. In contrast, nonsynonymous (replacement) nucleotide substitutions show a significant heterogeneity in distribution for both the same gene in different lineages and different genes in the same lineage. These major fluctuations in replacement but not silent substitution rates cannot be attributed to changes in mutation rate, suggesting that changes in the rate of globin polypeptide evolution in primates is not governed solely by variable mutation rates.      

Transactions of the One Hundredth Annual Meeting of The Canadian Medical Association: Part II

The purpose of this retrospective study was to compare (1) regular methadone withdrawal treatment and (2) prolonged methadone withdrawal treatment in 105 and 71 voluntary patients respectively, who attended the Narcotic Addiction Foundation (N.A.F.) between 1959 and mid-1964. Treatment consisted of individual counselling and medical care for all, and only residential care and psychiatric assessment for selected cases. The number of treatment sessions and the details of drug therapy are described.One hundred and fifty-three of 176 patients (87%) were interviewed approximately one to five years after the first clinic contact. Forty-three per cent showed some overall improvement in their behaviour. Rehabilitation was defined as change in a specific area—drug use, work, criminal behaviour, community associations, friendship patterns and family relationships—rather than in terms of abstention from drugs only. Age affected comparative results.     

Specificity of recA441-mediated (tif-1) mutational events.

Summary To investigate the impact of SOS induction on the distribution of spontaneous mutation, 111 recA441-mediated mutations were characterized at the DNA sequence level in the lacI gene of Escherichia coli. A 2.6-fold enhancement in lacI ^– mutation frequency was observed after induction of the SOS system in the absence of mutagenic treatment, and specific classes of mutational events were induced. G : C C : G, G : C T : A and A : T T : A transversion events were specifically enhanced after SOS induction. A preferential 5-Y-Purine-3 neighbouring base specificity for these transversion events is reported here (normalised for mutation of the purine residue). In addition, a preference for transversion events at 5-C/GTGG-3 sequences is also observed. Fifty events were recovered at the lacI frameshift hotspot site and were equally represented by 4 bp addition and deletion events. This 1:1 ratio deviates significantly from the 4:1 distribution characteristic of spontaneous frameshift mutation in the RecA⁺ background and is a consequence of the fourfold induction of the (–)4 event. This abberrant distribution was confirmed by oligomeric probing of 474 independent recA441-mediated spontaneous lacI ^– mutations.     

Mites of the familyMacrochelidae as predators of two species of dung-breeding pest flies

Nine species of macrochelid mites [Macrocheles “glaber” (Müller),M. aestivus Halliday,M. mammifer Berlese,M. peniculatus Berlese,M. robustulus (Berlese),M. merdarius (Berlese),M. peregrinus Krantz,M. eurygaster Krantz,Glyptholaspis confusa (Foà) were tested in the laboratory as predators of 2 species of dung-breeding pest flies (Musca vetustissima Walker,Haematobia irritans exigua de Meijere). The mites varied in their ability to attack the 2 fly species at both egg and larval stages. larger mites were generally more effective predators than the smaller species. The level of predation imposed byM. “glaber” onMusca vetustissima also varied with the developmental stage of both predator and prey.      

Failure of tachykinins including substance P and its fragments to influence proteoglycan and protein synthesis in bovine chondrocytes in vitro.

Adult bovine articular chondrocytes were exposed to substance P, neurokinins A and B or substance P fragments, SP1-4, SP1-6 and SP7-11 in vitro. Proteoglycan synthesis was assessed by measuring proteoglycans which were released into the culture medium or incorporated into the cell layer. The intact tachykinins or substance P fragments had no direct effect on proteoglycan synthesis. Nor was total protein production affected. Gel chromatography, under dissociative conditions, revealed that sulphated proteoglycans detected in the medium or cell layer following treatment of chondrocytes with substance P, contained proteoglycans of similar molecular weight to those produced by cells exposed only to diluent controls. Therefore, we conclude that the acceleration of arthritis by substance P does not appear to be mediated through an effect on chondrocyte synthetic function.     

Device for rapid quantification of human carotid baroreceptor-cardiac reflex responses

We designed, constructed, and evaluated a new device to characterize the human carotid baroreceptor-cardiac reflex response relation rapidly. We designed this system for study of reflex responses of astronauts before, during, and after space travel. The system comprises a new tightly sealing silicone rubber neck chamber, a stepping motor-driven electro-deposited nickel bellows pressure system, capable of delivering sequential R-wave-triggered neck chamber pressure changes between +40 and -65 mmHg, and a microprocessor-based electronics system for control of pressure steps and analysis and display of responses. This new system provokes classic sigmoid baroreceptor-cardiac reflex responses with threshold, linear, and saturation ranges in most human volunteers during one held expiration.