Bacterial Cell Division Regulation: Physiological Effects of Crystal Violet on Escherichia coli lon+ and lon− Strains

The Escherichia coli lon⁻ mutants apparently are defective in the ability to recommence cell division after temporary periods of deoxyribonucleic acid (DNA) synthesis inhibition. They are also more susceptible to cell division inhibition by the basic dye, crystal violet (CV), than are lon⁺ strains. In enriched broth, the lon⁺ strain continued to grow and divide in the presence of CV, but lon⁻ cell division was inhibited and filamentous growth resulted. In a supplemented minimal medium containing CV, lon⁻ cell division was only temporarily inhibited. There was no detectable specific effect on DNA synthesis, although CV slowed the rate of mass increase in both media. Trichloroacetic acid-insoluble lipid synthesis was preferentially inhibited in both lon⁺ and lon⁻ strains. In CV-containing enriched broth, diaminopimelic acid incorporation into trichloroacetic acid-insoluble compounds occurred at a rate greater than the rate of mass increase in both lon⁺ and lon⁻ strains. In a CV-containing supplemented minimal medium, diaminopimelic acid was incorporated to a greater extent by lon⁻ cells than by lon⁺ cells.     

Temperature-Sensitive Modification and Restriction Phenotypes of an Escherichia coli dnaD Mutant

A mutant of Escherichia coli temperature-sensitive for deoxyribonucleic acid synthesis, dnaD, was found to have temperature-sensitive modification and restriction phenotypes. In contrast to the original observation by Carl (1970), the mutant could support the growth of λ phage at 41 C. However, the λ phages thus produced were able to form plaques with normal plating efficiency only on E. coli C, a restriction-less strain, but not on E. coli K. Since the λ phages produced in the mutant at 30 C could form plaques equally well on both E. coli strains, it was concluded that the dnaD mutant has a temperature-sensitive modification phenotype. Furthermore, since the dnaD mutant allowed some growth of unmodified λ·C phages at 41 C but less at 30 C, the mutant is also temperature sensitive in restriction. The relationship, if any, between temperature-sensitive deoxyribonucleic acid synthesis and temperature-sensitive modification-restriction in the dnaD mutant is not known. Similar experiments were done with three dnaC mutants and one dnaA mutant. Two dnaC mutants were found to have altered restriction phenotypes at 41 C, but none of the mutants were defective in modification.     

Action spectrum for an enhancement of endogenous respiration by light in chlorella

The oxygen consumption of a starved chlorophyll-free, yellow mutant of Chlorella vulgaris is enhanced by very small amounts of blue light (λ 450 mμ); a saturation level is reached at about 500 ergs cm⁻² sec⁻¹. At that intensity the respiration is about 3 times greater than in the dark. An action spectrum for the enhancement of respiration shows 2 peaks around λ 450 and 375 mμ. Flavins and cis-carotenoids are discussed as the pigments involved.     

Lambda CIN-1, a New Mutation Which Enhances Lysogenization by Bacteriophage Lambda, and the Genetic Structure of the Lambda CY Region

Seven lambda cy mutants have been mapped within a small region located approximately halfway between the rightward boundary of the imm⁴³⁴ region and the lambda cII gene. The seven mutants lie at four sites separated by a total distance of about 12 nucleotide pairs, as estimated from recombination frequencies. Six of the seven mutants lie on the right side of the cy fine structure map, spanning a total distance of about 3–5 nucleotide pairs. Lying approximately 11–21 nucleotide pairs to the left of the leftmost cy mutant is a newly described mutation called cin-1, for c independent. The cin-1 mutation allows some lysogenization when coupled with any cy, cII or cIII mutant, but not when coupled with a defective cI gene. The cin-1 mutation, like cy mutants, has a cis-dominant action upon the cI gene in mixed infections. The observation that λimm⁴³⁴ cin-1 cy2001 lysogenizes efficiently, but not λimm⁴³⁴ cin-1 cy2001 cII68 nor any other λimm⁴³⁴ cin-1 cy derivative, is interpreted to mean that all of the cy mutants on the right side of the cy fine structure map inactivate a binding site for cII/cIII function, but that cy2001, the single mutant on the left side of the cy fine structure map, does not inactivate that binding site.     

The proportion of mutants in bacterial cultures

The proportion of mutants in a growing culture of organisms will depend upon (a) the rate at which the wild cells produce them (with or without growth), (b) the back mutation rate, and (c) the growth rates of the wild and mutant cells. If the mutation rate without growth and the back mutation rate are neglected, the growth of a mutant is expressed by See PDF for Equation and the ratio of the mutant to wild by See PDF for Equation in which λ = mutation frequency rate constant, "mutation rate," A = growth rate constant of wild cells W, B = growth rate constant of mutant cells M. If the term [B – (1 – 2λ)A] is positive, the proportion of mutants increases continuously. If it is negative, the proportion of mutants reaches a constant value See PDF for Equation If mutation is assumed to occur without growth at the rate C, then the corresponding equations are (11), (12), and (14). See PDF for Equation If (B + C – A) is negative and t = ∞, See PDF for Equation If C << A, See PDF for Equation     

The proportion of terramycin-resistant mutants in B. megatherium cultures

The number of terramycin-resistant mutants in Bacillus megatherium cultures, their mutation rate, and the growth rate of the wild and mutant cells have been determined under various conditions. These values are in agreement with the following equations (Northrop and Kunitz, 1957):— See PDF for Equation λ = mutation rate, A = growth rate constant of wild cells, B = growth rate constant of mutants, See PDF for Equation equilibrium. The value of the mutation rate as determined from equation (6) agrees with that found by the null fraction method.     

Molecular Mechanism of Heat Shock-Provoked Disassembly of the Coliphage λ Replication Complex

We have found previously that, in contrast to the free O initiator protein of λ phage or plasmid rapidly degraded by the Escherichia coli ClpP/ClpX protease, the λO present in the replication complex (RC) is protected from proteolysis. However, in cells growing in a complete medium, a temperature shift from 30 to 43°C resulted in the decay of the λO fraction, which indicated disassembly of RC. This process occurred due to heat shock induction of the groE operon, coding for molecular chaperones of the Hsp60 system. Here we demonstrate that an increase in the cellular concentration of GroEL and GroES proteins is not in itself sufficient to cause RC disassembly. Another requirement is a DNA gyrase-mediated negative resupercoiling of λ plasmid DNA, which counteracts DNA relaxation and starts to dominate 10 min after the temperature upshift. We presume that RC dissociates from λ DNA during the negative resupercoiling, becoming susceptible to the subsequent action of GroEL/S and ClpP/ClpX proteins. In contrast to λcro⁺, in λcro⁻ plasmid-harboring cells, the RC reveals heat shock resistance. After temperature upshift of the λcrots plasmid-harboring cells, a Cro repressor-independent control of λ DNA replication and heat shock resistance of RC are established before the period of DNA gyrase-mediated negative supercoiling. We suggest that the tight binding of RC to λ DNA is due to interaction of RC with other DNA-bound proteins, and is related to the molecular basis of the λcro⁻ plasmid replication control.     

Identifying DNA Mutations in Purified Hematopoietic Stem/Progenitor Cells

In recent years, it has become apparent that genomic instability is tightly related to many developmental disorders, cancers, and aging. Given that stem cells are responsible for ensuring tissue homeostasis and repair throughout life, it is reasonable to hypothesize that the stem cell population is critical for preserving genomic integrity of tissues. Therefore, significant interest has arisen in assessing the impact of endogenous and environmental factors on genomic integrity in stem cells and their progeny, aiming to understand the etiology of stem-cell based diseases.LacI transgenic mice carry a recoverable λ phage vector encoding the LacI reporter system, in which the LacI gene serves as the mutation reporter. The result of a mutated LacI gene is the production of β-galactosidase that cleaves a chromogenic substrate, turning it blue. The LacI reporter system is carried in all cells, including stem/progenitor cells and can easily be recovered and used to subsequently infect E. coli. After incubating infected E. coli on agarose that contains the correct substrate, plaques can be scored; blue plaques indicate a mutant LacI gene, while clear plaques harbor wild-type. The frequency of blue (among clear) plaques indicates the mutant frequency in the original cell population the DNA was extracted from. Sequencing the mutant LacI gene will show the location of the mutations in the gene and the type of mutation.The LacI transgenic mouse model is well-established as an in vivo mutagenesis assay. Moreover, the mice and the reagents for the assay are commercially available. Here we describe in detail how this model can be adapted to measure the frequency of spontaneously occurring DNA mutants in stem cell-enriched Lin^-IL7R^-Sca-1⁺cKit⁺⁺(LSK) cells and other subpopulations of the hematopoietic system.     

Targeted disruption of the Wnt regulator Kremen induces limb defects and high bone density

Kremen1 and Kremen2 (Krm1 and Krm2) are transmembrane coreceptors for Dickkopf1 (Dkk1), an antagonist of Wnt/β-catenin signaling. The physiological relevance of Kremen proteins in mammals as Wnt modulators is unresolved. We generated and characterized Krm mutant mice and found that double mutants show enhanced Wnt signaling accompanied by ectopic postaxial forelimb digits and expanded apical ectodermal ridges. Triple mutant Krm1^−/− Krm2^−/− Dkk1^+/− mice show enhanced growth of ectopic digits, indicating that Dkk1 and Krm genes genetically interact during limb development. Wnt/β-catenin signaling also plays a critical role in bone formation. Single Krm mutants show normal bone formation and bone mass, while double mutants show increased bone volume and bone formation parameters. Our study provides the first genetic evidence for a functional interaction of Kremen proteins with Dkk1 as negative regulators of Wnt/β-catenin signaling and reveals that Kremen proteins are not universally required for Dkk1 function.     

The Impact of Alpha-Syntrophin Deletion on the Changes in Tissue Structure and Extracellular Diffusion Associated with Cell Swelling under Physiological and Pathological Conditions

Aquaporin-4 (AQP4) is the primary cellular water channel in the brain and is abundantly expressed by astrocytes along the blood-brain barrier and brain-cerebrospinal fluid interfaces. Water transport via AQP4 contributes to the activity-dependent volume changes of the extracellular space (ECS), which affect extracellular solute concentrations and neuronal excitability. AQP4 is anchored by α-syntrophin (α-syn), the deletion of which leads to reduced AQP4 levels in perivascular and subpial membranes. We used the real-time iontophoretic method and/or diffusion-weighted magnetic resonance imaging to clarify the impact of α-syn deletion on astrocyte morphology and changes in extracellular diffusion associated with cell swelling in vitro and in vivo. In mice lacking α-syn, we found higher resting values of the apparent diffusion coefficient of water (ADC_W) and the extracellular volume fraction (α). No significant differences in tortuosity (λ) or non-specific uptake (k′), were found between α-syn-negative (α-syn −/−) and α-syn-positive (α-syn +/+) mice. The deletion of α-syn resulted in a significantly smaller relative decrease in α observed during elevated K⁺ (10 mM) and severe hypotonic stress (−100 mOsmol/l), but not during mild hypotonic stress (−50 mOsmol/l). After the induction of terminal ischemia/anoxia, the final values of ADC_W as well as of the ECS volume fraction α indicate milder cell swelling in α-syn −/− in comparison with α-syn +/+ mice. Shortly after terminal ischemia/anoxia induction, the onset of a steep rise in the extracellular potassium concentration and an increase in λ was faster in α-syn −/− mice, but the final values did not differ between α-syn −/− and α-syn +/+ mice. This study reveals that water transport through AQP4 channels enhances and accelerates astrocyte swelling. The substantially altered ECS diffusion parameters will likely affect the movement of neuroactive substances and/or trophic factors, which in turn may modulate the extent of tissue damage and/or drug distribution.     

Coordination of Initiation of Nuclear Division and Initiation of Cell Division in Schizosaccharomyces pombe: Genetic Interactions of Mutations

sep1⁺ encodes a Schizosaccharomyces pombe homolog of the HNF-3/forkhead family of the tissue-specific and developmental gene regulators identified in higher eukaryotes. Its mutant allele sep1-1 causes a defect in cytokinesis and confers a mycelial morphology. Here we report on genetic interactions of sep1-1 with the M-phase initiation mutations wee1⁻, cdc2-1w, and cdc25-22. The double mutants sep1-1 wee1⁻ and sep1-1 cdc2-1w form dikaryon cells at high frequency, which is due to nuclear division in the absence of cell division. The dikaryosis is reversible and suppressible by cdc25-22. We propose that the genes wee1⁺, cdc2⁺, cdc25⁺, and sep1⁺ form a regulatory link between the initiation of mitosis and the initiation of cell division.     

Lytic Replication of Coliphage Lambda in Salmonella typhosa Hybrids

Hybrids between Escherichia coli K-12 and Salmonella typhosa which conserved a continuous K-12 chromosomal diploid segment extending from pro through ara to the strA locus were sensitive to plaque formation by wild-type λ. These partially diploid S. typhosa hybrids could be lysogenized with λ and subsequently induced to produce infectious phage particles. When the K-12 genes were segregated from a lysogenic S. typhosa hybrid, phage-productive ability was no longer detectable due to loss of a genetic region necessary for vegetative replication of λ. However, λ prophage was shown to persist in a quiescent state in the S. typhosa hybrid segregant with phage-productive ability being reactivated after replacement of the essential K-12 λ replication region. Low-frequency transduction and high-frequency transduction lysates containing the gal⁺ genes of S. typhosa were prepared by induction of λ-lysogenic S. typhosa hybrids indicating that the attλ site is chromosomally located in S. typhosa in close proximity to the gal locus as in E. coli K-12. After propagation in S. typhosa hybrids, λ was subject to restriction by E. coli K-12 recipients, thus establishing that S. typhosa does not perform the K-12 modification of λ deoxyribonucleic acid. Hybrids of S. typhosa, however, did not restrict λ grown previously on E. coli K-12. The K-12 genetic region required for λ phage production in S. typhosa was located within min 66 to min 72 on the genetic map of the E. coli chromosome. Transfer of an F-merogenote encompassing the 66 to 72 min E. coli chromosomal region to λ-insensitive S. typhosa hybrids enabled them to replicate wild-type λ. The λ-insensitive S. typhosa hybrid, WR4255, which blocks λ replication, can be mutagenized to yield mutant strains sensitive to λvir and λimm434. These WR4255 mutants remained insensitive to plaque formation by wild-type λ.     

Host Specificity of Salmonella typhimurium Deoxyribonucleic Acid Restriction and Modification

The restriction and modification genes of Salmonella typhimurium which lie near the thr locus were transferred to a restrictionless mutant of Escherichia coli. These genes were found to be allelic to the E. coli K, B, and A restriction and modification genes. E. coli recombinants with the restriction and modification host specificity of S. typhimurium restricted phage λ that had been modified by each of the seven known host specificities of E. coli at efficiency of plating levels of about 10⁻². Phage λ modified with the S. typhimurium host specificity was restricted by six of the seven E. coli host specificities but not by the RII (fi⁻ R-factor controlled) host specificity. It is proposed that the restriction and modification enzymes of this S. typhimurium host specificity have two substrates, one of which is a substrate for the RII host specificity enzymes.     

Iron Triggers λSo Prophage Induction and Release of Extracellular DNA in Shewanella oneidensis MR-1 Biofilms

Prophages are ubiquitous elements within bacterial chromosomes and affect host physiology and ecology in multiple ways. We have previously demonstrated that phage-induced lysis is required for extracellular DNA (eDNA) release and normal biofilm formation in Shewanella oneidensis MR-1. Here, we investigated the regulatory mechanisms of prophage λSo spatiotemporal induction in biofilms. To this end, we used a functional fluorescence fusion to monitor λSo activation in various mutant backgrounds and in response to different physiological conditions. λSo induction occurred mainly in a subpopulation of filamentous cells in a strictly RecA-dependent manner, implicating oxidative stress-induced DNA damage as the major trigger. Accordingly, mutants affected in the oxidative stress response (ΔoxyR) or iron homeostasis (Δfur) displayed drastically increased levels of phage induction and abnormal biofilm formation, while planktonic cells were not or only marginally affected. To further investigate the role of oxidative stress, we performed a mutant screen and identified two independent amino acid substitutions in OxyR (T104N and L197P) that suppress induction of λSo by hydrogen peroxide (H₂O₂). However, λSo induction was not suppressed in biofilms formed by both mutants, suggesting a minor role of intracellular H₂O₂ in this process. In contrast, addition of iron to biofilms strongly enhanced λSo induction and eDNA release, while both processes were significantly suppressed at low iron levels, strongly indicating that iron is the limiting factor. We conclude that uptake of iron during biofilm formation triggers λSo-mediated lysis of a subpopulation of cells, likely by an increase in iron-mediated DNA damage sensed by RecA.     

Novel Reporter Alleles of GSK-3α and GSK-3β

Glycogen Synthase Kinase 3 (GSK-3) is a key player in development, physiology and disease. Because of this, GSK-3 inhibitors are increasingly being explored for a variety of applications. In addition most analyses focus on GSK-3β and overlook the closely related protein GSK-3α. Here, we describe novel GSK-3α and GSK-3β mouse alleles that allow us to visualise expression of their respective mRNAs by tracking β-galactosidase activity. We used these new lacZ alleles to compare expression in the palate and cranial sutures and found that there was indeed differential expression. Furthermore, both are loss of function alleles and can be used to generate homozygous mutant mice; in addition, excision of the lacZ cassette from GSK-3α creates a Cre-dependent tissue-specific knockout. As expected, GSK3α mutants were viable, while GSK3β mutants died after birth with a complete cleft palate. We also assessed the GSK-3α mutants for cranial and sternal phenotypes and found that they were essentially normal. Finally, we observed gestational lethality in compound GSK-3β^−/−; GSK3α^+/− mutants, suggesting that GSK-3 dosage is critical during embryonic development.     

VR09 Cell Line: An EBV-Positive Lymphoblastoid Cell Line with In Vivo Characteristics of Diffuse Large B Cell Lymphoma of Activated B-Cell Type

Background

small B-cell neoplasms can show plasmacytic differentiation and may potentially progress to aggressive lymphoma (DLBCL). Epstein-Barr virus (EBV) infection may cause the transformation of malignant cells in vitro.

Design and Method

we established VR09 cell line with plasmacytic differentiation, obtained from a case of atypical, non-CLL B-cell chronic lymphoproliferative disease with plasmacytic features. We used flow cytometry, immunohistochemistry, polymerase chain reaction, cytogenetic analysis and florescence in situ hybridization in the attempt at thoroughly characterizing the cell line. We showed VR09 tumorigenic potential in vivo, leading to the development of activated DLBCL with plasmacytic features.

Results

VR09 cells displayed plasmacytic appearance and grew as spherical tumors when inoculated subcutaneously into immunodeficient Rag2^−/− γ-chain^−/− mice. VR09 cell line and tumors displayed the phenotype of activated stage of B cell maturation, with secretory differentiation (CD19+ CD20+ CD79a+ CD79b+/− CD138+ cyclin D1- Ki67 80% IgM+ IgD+ MUM1+ MNDA+ CD10- CD22+ CD23+ CD43+ K+, λ- Bcl2+ Bcl6-) and they presented episomal EBV genome, chromosome 12 trisomy, lack of c-MYC rearrangement and Myd88 gene mutation, presence of somatic hypermutation in the VH region, and wild-type p53.

Conclusion

This new EBV-positive cell line may be useful to further characterize in vivo activated DLBCL with plasmacytic features.     

Physiological Role of β-Phosphoglucomutase in Lactococcus lactis

A β-phosphoglucomutase (β-PGM) mutant of Lactococcus lactis subsp. lactis ATCC 19435 was constructed using a minimal integration vector and double-crossover recombination. The mutant and the wild-type strain were grown under controlled conditions with different sugars to elucidate the role of β-PGM in carbohydrate catabolism and anabolism. The mutation did not significantly affect growth, product formation, or cell composition when glucose or lactose was used as the carbon source. With maltose or trehalose as the carbon source the wild-type strain had a maximum specific growth rate of 0.5 h⁻¹, while the deletion of β-PGM resulted in a maximum specific growth rate of 0.05 h⁻¹ on maltose and no growth at all on trehalose. Growth of the mutant strain on maltose resulted in smaller amounts of lactate but more formate, acetate, and ethanol, and approximately 1/10 of the maltose was found as β-glucose 1-phosphate in the medium. Furthermore, the β-PGM mutant cells grown on maltose were considerably larger and accumulated polysaccharides which consisted of α-1,4-bound glucose units. When the cells were grown at a low dilution rate in a glucose and maltose mixture, the wild-type strain exhibited a higher carbohydrate content than when grown at higher growth rates, but still this content was lower than that in the β-PGM mutant. In addition, significant differences in the initial metabolism of maltose and trehalose were found, and cell extracts did not digest free trehalose but only trehalose 6-phosphate, which yielded β-glucose 1-phosphate and glucose 6-phosphate. This demonstrates the presence of a novel enzymatic pathway for trehalose different from that of maltose metabolism in L. lactis.