Plasmid evolution and interaction between the plasmid addiction stability systems of two related broad-host-range IncQ-like plasmids

Plasmid pTC-F14 contains a plasmid stability system called pas (plasmid addiction system), which consists of two proteins, a PasA antitoxin and a PasB toxin. This system is closely related to the pas of plasmid pTF-FC2 (81 and 72% amino acid identity for PasA and PasB, respectively) except that the pas of pTF-FC2 contains a third protein, PasC. As both pTC-F14 and pTF-FC2 are highly promiscuous broad-host-range plasmids isolated from bacteria that share a similar ecological niche, the plasmids are likely to encounter each other. We investigated the relative efficiencies of the two stability systems and whether they had evolved apart sufficiently for each pas to stabilize a plasmid in the presence of the other. The three-component pTF-FC2 pas was more efficient at stabilization of a heterologous tester plasmid than the two component pas of pTC-F14 in Escherichia coli host cells (+/- 92% and +/- 60% after 100 generations, respectively). The PasA antidote of each pas was unable to neutralize the PasB toxin of the other plasmid. The pas proteins of each plasmid autoregulated their own expression as well as that of the pas of the other plasmid. The pas of pTF-FC2 was more effective at repressing the pas operon of pTC-F14 than the pas of pTC-F14 was able to repress itself or the pas of pTF-FC2. This increased efficiency was not due to the PasC of pTF-FC2. The effect of this stronger repression was that pTF-FC2 displaced pTC-F14 when the two plasmids were coresident in the same E. coli host cell. Plasmid curing resulted in the arrest of cell growth but did not cause cell death, and plasmid stability was not influenced by the E. coli mazEF genes.     

Reduction in interaction between cGMP and cAMP in dog ventricular myocytes with hypertrophic failure

Baseline function and signal transduction are depressed in hearts with hypertrophic failure. We tested the hypothesis that the effects of cGMP and its interaction with cAMP would be reduced in cardiac myocytes from hypertrophic failing hearts. Ventricular myocytes were isolated from control dogs, dogs with aortic valve stenosis hypertrophy, and dogs with pacing hypertrophic failure. Myocyte function was measured using a video edge detector. Cell contraction data were obtained at baseline, with 8-bromo-cGMP (10(-7), 10(-6), and 10(-5) M), with erythro-9-(2-hydroxy-3-nonyl)adenine [EHNA; a cAMP phosphodiesterase (PDE(2)) inhibitor] plus 8-bromo-cGMP, or milrinone (a PDE(3) inhibitor) plus 8-bromo-cGMP. Baseline percent shortening and maximal rates of shortening (R(max)) and relaxation were slightly reduced in hypertrophic myocytes and were significantly lower in failing myocytes (R(max): control dogs, 95.3 +/- 17.3; hypertrophy dogs, 88.2 +/- 5.5; failure dogs, 53.2 +/- 6.4 mum/s). 8-Bromo-cGMP dose dependently reduced myocyte function in all groups. However, EHNA (10(-6) M) and milrinone (10(-6) M) significantly reduced the negative effects of cGMP on cell contractility in control and hypertrophy but not in failing myocytes (R(max) for control dogs: cGMP, -46%; +EHNA, -21%; +milrinone, -19%; for hypertrophy dogs: cGMP, -40%; +EHNA, -13%; +milrinone, -20%; for failure dogs: cGMP, -40%; +EHNA, -29%; +milrinone, -32%). Both combinations of EHNA-cGMP and milrinone-cGMP significantly increased intracellular cAMP in control, hypertrophic, and failing myocytes. These data indicated that the cGMP signaling pathway was preserved in hypertrophic failing cardiac myocytes. However, the interaction of cGMP with the cAMP signaling pathway was impaired in these failing myocytes.     

The interaction between two oppositely charged polyelectrolytes

Mixtures of a weak polybase (polyethylenimine) and a weak polyacid acrylamide-acrylic acid copolymer in aqueous solutions at several ionic strengths and polymer concentrations are studied potentiometrically. When the concentrations of the polyethylenimine and acrylamide-acrylic acid copolymer charges are not too different, phase separation into two liquid phases (“complex coacervation”) is observed. In the pH region where no phase separation occurs, potentiometric titrations are performed on mixtures of both polymers. From the titrations of polyethylenimine solutions, acrylamide-acrylic acid copolymer solutions, and the mixtures, the free energy of interaction has been evaluated according to the theory of Litan. The dependence of the free energy of interaction on pH, polymer concentrations, and ionic strength is explained quantitatively with a model of cooperative electrostatic physical association.     

Test for interaction between two unlinked loci

Despite the growing consensus on the importance of testing gene-gene interactions in genetic studies of complex diseases, the effect of gene-gene interactions has often been defined as a deviance from genetic additive effects, which is essentially treated as a residual term in genetic analysis and leads to low power in detecting the presence of interacting effects. To what extent the definition of gene-gene interaction at population level reflects the genes' biochemical or physiological interaction remains a mystery. In this article, we introduce a novel definition and a new measure of gene-gene interaction between two unlinked loci (or genes). We developed a general theory for studying linkage disequilibrium (LD) patterns in disease population under two-locus disease models. The properties of using the LD measure in a disease population as a function of the measure of gene-gene interaction between two unlinked loci were also investigated. We examined how interaction between two loci creates LD in a disease population and showed that the mathematical formulation of the new definition for gene-gene interaction between two loci was similar to that of the LD between two loci. This finding motived us to develop an LD-based statistic to detect gene-gene interaction between two unlinked loci. The null distribution and type I error rates of the LD-based statistic for testing gene-gene interaction were validated using extensive simulation studies. We found that the new test statistic was more powerful than the traditional logistic regression under three two-locus disease models and demonstrated that the power of the test statistic depends on the measure of gene-gene interaction. We also investigated the impact of using tagging SNPs for testing interaction on the power to detect interaction between two unlinked loci. Finally, to evaluate the performance of our new method, we applied the LD-based statistic to two published data sets. Our results showed that the P values of the LD-based statistic were smaller than those obtained by other approaches, including logistic regression models.     

Electrostatic interaction between two charged spherical molecules

An explicit analytic expression is obtained for the electrostatic energy of the interaction between two ion-impenetrable space-charged hard spheres as a model for spherical molecules in an electrolyte solution on the basis of the linearized Poisson-Boltzmann equation. An explicit expression for the potential distribution in a 3D-space is also found. The polarization effects due to the mutual influence between the spheres are taken into account. The analysis is done by assuming different dielectric permittivities of the respective spheres and of the solution as well. It is shown that the correction terms in the expression for the total energy of interaction arising from the polarization effects always correspond to forces of attraction between the spheres. The contribution of these terms to the total energy of interaction depends on the distance between the two spheres and the dielectric permittivities of the spheres and the solution as well as on the electrolyte concentration in the solution. A numerical simulation of the potential field topography is carried out at several values of the Debye-Hückel parameter. It is shown that the polarization effect can produce significant changes in the potential distribution in the case of strong interacting spheres.     

Indirect population interaction between two aphid species

We designed an experiment to test whether two species of aphid feeding on different species of host plant influence each others population dynamics via shared parasitoids (apparent competition) or other indirect processes. Pea aphid ( Acyrthosiphon pisum ) colonies declined faster towards mid-summer when there were nearby colonies of nettle aphid ( Microlophium carnosum ), though the significance of the difference ( P  = 0.06) was just short of the traditional 0.05 level. Observations suggested that parasitoids were not responsible for this difference, however, and that it was highly likely to be caused by aphid-specific predators.     

In vivo interaction between mouse liver lysosomes and chloroquine

Particles sedimenting at 27,000 g X 10 min (MLCQ) were separated from liver homogenates of mice injected with chloroquine (CQ). The MLCQ contained most of the drug recovered in the organ as well as 50% of the liver aryl sulphatase activity. The release of CQ from MLCQ was studied in some physicochemical conditions, and in the presence of various agents known to modify membrane composition and stability. At pH 7.4, the equilibrium between free and bound CQ depended on the dilution of the MLCQ, and the time to reach equilibrium was strongly influenced by the temperature of incubation. Several agents causing membrane disruption and lysosomal enzyme leakage, such as osmotic shock, sonication and digitonin, had little effect on the CQ release. Acid and alkaline buffers, 0.55 M KCl and 0.1% Triton X-100 caused, instead, the immediate release of most of the bound CQ. Concentrations of digitonin causing the release of aryl sulphatase activity had little effect on bound CQ, suggesting that the drug is retained in lysosomes by forces and/or structures different in nature from those retaining most of the lysosomal enzyme activity. We think that the CQ trapped in lysosomes is bound to high affinity sites in membranous structures which are particularly altered by agents known to extract peripheral proteins from biological membranes or to change the conformation of molecular structures.     

An EAL domain protein and cyclic AMP contribute to the interaction between the two quorum sensing systems in Escherichia coli

Quorum sensing (QS) is a bacterial cell-cell communication process by which bacteria communicate using extracellular signals called autoinducers. Two QS systems have been identified in Escherichia coli K-12, including an intact QS system 2 that is stimulated by the cyclic AMP (cAMP)-cAMP receptor protein (CRP) complex and a partial QS system 1 that consists of SdiA (suppressor of cell division inhibitor) responding to signals generated by other microbial species. The relationship between QS system 1 and system 2 in E. coli, however, remains obscure. Here, we show that an EAL domain protein, encoded by ydiV, and cAMP are involved in the interaction between the two QS systems in E. coli. Expression of sdiA and ydiV is inhibited by glucose. SdiA binds to the ydiV promoter region in a dose-dependent, but nonspecific, manner; extracellular autoinducer 1 from other species stimulates ydiV expression in an sdiA-dependent manner. Furthermore, we discovered that the double sdiA-ydiV mutation, but not the single mutation, causes a 2-fold decrease in intracellular cAMP concentration that leads to the inhibition of QS system 2. These results indicate that signaling pathways that respond to important environmental cues, such as autoinducers and glucose, are linked together for their control in E. coli.     

Segmental vascular resistances and compliances in dog lung

The segmental distribution of vascular resistances and compliances were evaluated in isolated blood perfused lung lobes using arterial, venous, and double-occlusion pressures and were compared with filtration midpoint capillary pressures (Pc,f). We separated total vascular resistance (RT) and compliance (CT) into large artery (Ra, Ca), large vein (Rv, Cv), and microvascular compartments (Rmc, Cmc) at base-line and increased vascular pressures and during infusions of histamine, serotonin, and norepinephrine. In control lobes, double-occlusion pressure (Pdo) closely approximated Pc,f at all vascular pressures. Pre- and postcapillary resistance were approximately equal when referenced to either Pc,f or Pdo. Although Rmc comprised 42% of RT and Cmc constituted 76% of CT, a twofold increase in base-line Pc,f caused RT to decrease to 67% and Rmc/RT to 29% of control values, whereas CT decreased to 87% and Cmc/CT decreased to 88% of control values over the same Pc,f range. Mean static CT was 2.25 +/- 0.09 ml X cmH2O-1. 100 g-1, whereas dynamic CT was 1.54 +/- 0.08 ml X cmH2O-1. 100 g-1, or only 68% of static vascular compliance. Drug infusions increased mean RT from 4.2- to 5.3-fold and significantly decreased both static and dynamic CT. Although all vascular segments were constricted, histamine affected primarily large veins, serotonin increased Ra greater than Rv, and norepinephrine constricted upstream and downstream vessels about equally. Increased Pc,f in the presence of these drugs decreased RT significantly in every case primarily through attenuation of the drug vasoconstrictor effect on Rmc and decreased CT primarily due to a decrease in Cmc, but increased Cmc/(Ca + Cv). Thus the microvascular compartment appears to be the major site of both fluid filtration and vascular compliance and contributes significantly to total vascular resistance. Drug infusions constricted large and small vessel compartments as defined here, but increased Pc,f attenuated microvascular vasoconstriction and to a lesser extent large vessel vasoconstriction resulting in a reduced microvascular resistance in both drug-treated and control lobes. This effect can be attributed to recruitment and/or distension of microvessels and distension of larger vessels.     

A redox-dependent interaction between two electron-transfer partners involved in photosynthesis

Ferredoxin:NADP⁺:reductase (FNR) catalyzes one terminal step of the conversion of light energy into chemical energy during photosynthesis. FNR uses two high energy electrons photoproduced by photosystem I (PSI) and conveyed, one by one, by a ferredoxin (Fd), to reduce NADP⁺ to NADPH. The reducing power of NADPH is finally involved in carbon assimilation. The interaction between oxidized FNR and Fd was studied by crystallography at 2.4 Å resolution leading to a three-dimensional picture of an Fd–FNR biologically relevant complex. This complex suggests that FNR and Fd specifically interact prior to each electron transfer and disassemble upon a redox-linked conformational change of the Fd.     

The interaction between two charged rods in an electrolyte solution

A problem on the electrostatic interaction of two homogeneously charged macromolecular rods of a finite length, submerged into an electrolyte solution was considered. An explicit expression for the energy of interaction and rotational moment as a function of the angle of rotation between the long axes of the molecules was obtained. At small angles of rotation, the expression for energy turns into the corresponding formula for parallel rods, and the rotational moment tends to zero, as it follows from geometrical considerations. The possibility is discussed whether the study is applicable to real biological systems, including liquid-crystalline dispersions of DNA.     

On the interaction in culture between two pathogenic soil-inhabiting fungi

Summary Interaction betweenFusarium vasinfectum andMacrophomina phaseoli was studied on solid and in liquid media at varying cultural conditions, in an attempt to explain the reduction in virulence of each fungus when the two pathogens were mixed together in the soil. Metabolites produced by each fungus in liquid media were suppressive to the growth of the other. Such suppression was influenced by the pH factor. Saltation ofFusarium was favoured by the presence ofMacrophomina metabolites.Dedicated to ProfessorTibor Benedek on the occasion of his 70th birthday.     

The interaction between hemoglobin and two surfactants with different charges

The interactions of hemoglobin (Hb) with sodium dodecyl sulfate (SDS) and dodecyl trimethylammonium bromide (DTAB) are investigated by several methods. We observed the formation of hemichrome below the critical micelle concentration (cmc) of surfactant and the release of heme from Hb above the cmc. When pH value of Hb/surfactant system is lower than isoelectric point (pI) of Hb, the interaction of SDS with Hb is both electrostatic and hydrophobic, while the interaction of DTAB with Hb is hydrophobic mainly. On the contrary, when pH > pI, the interaction of SDS with Hb is hydrophobic mainly, while the interaction of DTAB with Hb is both electrostatic and hydrophobic. In the case where both the electrostatic interaction and hydrophobic interaction exist, the electrostatic interaction plays a more important role. Thus, SDS tends to interact with Hb more obviously than DTAB does when pH < pI and the interaction between DTAB and Hb is stronger when pH > pI.