Chemotactic properties of Escherichia coli mutants having abnormal Ca2+ content

The calA, calC, and calD mutants of Escherichia coli are known to be sensitive to Ca2+ (R. N. Brey and B. P. Rosen, J. Bacteriol. 139:824-834, 1979). In the absence of any added stimuli for chemotaxis, both the calC and the calD mutants swam with a tumbly bias. Both the calC and the calD mutants were defective in chemotaxis as measured by computer analysis, use of swarm plates, and capillary assays. The calA mutant was only slightly defective in motility and only slightly impaired in chemotaxis. Chemotactically wild-type cells had an intra-cellular free-Ca2+ level of about 105 nM. The intracellular free-Ca2+ levels of the mutants, as determined by use of the fluorescent Ca2+ indicator dye fura-2 or fluo-3, were about 90, about 1,130, and about 410 nM for calA, calC, and calD, respectively. Lowering the intracellular free-Ca2+ levels in wild-type cells and in the tumbly cal mutants by use of Ca2+ chelators promoted running (smooth swimming). Overexpression of CheZ (which causes dephosphorylation of CheY-phosphate) in the wild type and in the tumbly cal mutants decreased the level of tumbliness (which is caused by CheY-phosphate). The calA mutant was 4- to 10-fold more resistant than the wild type to the inhibitory effect of omega-conotoxin on chemotaxis. omega-Conotoxin had no effect on Ca2+ extrusion by wild-type E. coli; that result suggests that omega-conotoxin affects Ca2+ transport at the point of entry instead of exit

Maximal and inextensible polynomials and the geometry of the spectra of normal operators

We consider the set S(n,0) of monic complex polynomials of degree $n\ge 2$ having all their zeros in the closed unit disk and vanishing at 0. For $p\in S(n,0)$ we let $|p|_{0}$ denote the distance from the origin to the zero set of $p'$. We determine all 0-maximal polynomials of degree $n$, that is, all polynomials $p\in S(n,0)$ such that $|p|_{0}\ge |q|_{0}$ for any $q\in S(n,0)$. Using a second order variational method we then show that although some of these polynomials are inextensible, they are not necessarily locally maximal for Sendov's conjecture. This invalidates the recently claimed proofs of the conjectures of Sendov and Smale and shows that the method used in these proofs can only lead to (already known) partial results. In the second part of the paper we obtain a characterization of the critical points of a complex polynomial by means of multivariate majorization relations. We also propose an operator theoretical approach to Sendov's conjecture, which we formulate in terms of the spectral variation of a normal operator and its compression to the orthogonal complement of a trace vector. Using a theorem of Gauss-Lucas type for normal operators, we relate the problem of locating the critical points of complex polynomials to the more general problem of describing the relationships between the spectra of normal matrices and the spectra of their principal submatrices.Comment: A condensed version of the first half of this paper appeared in Math. Scand., see arXiv:math/0601600. Parts of the second half appeared in Trans. Amer. Math. Soc., see arXiv:math/0601519. The current version contains the full details of the counterexample constructions and some other result

Inhibition of Escherichia coli chemotaxis by omega-conotoxin, a calcium ion channel blocker

Escherichia coli chemotaxis was inhibited by omega-conotoxin, a calcium ion channel blocker. With Tris-EDTA-permeabilized cells, nanomolar levels of omega-conotoxin inhibited chemotaxis without loss of motility. Cells treated with omega-conotoxin swam with a smooth bias, i.e., tumbling was inhibited

Mitochondrially-Encoded Adenosine Triphosphate Synthase 6 Gene Haplotype Variation Among World Population During 2003-2013

Background: Adaptation and natural selection serve as an important part of evolution. Adaptation in molecular level can lead to genetic drift which causes mutation of genetic material; one of which is polymorphism of mitochondrial DNA (mtDNA). The aim of this study is to verify the polymorphism of mitochondrially-encoded Adenosine Triphosphate synthase6gene (MT-ATP6) as one of mtDNA building blocks among tropic, sub-tropic, and polar areas. Methods: This descriptive quantitative research used 3,210 mtDNA sequences, taken from GenBank, as secondary data from 27 different populations. The data were grouped into 3 population groups based on the climates of their location. After grouping, the sequences were then aligned and trimmed using Unipro EUGENE, and analysed by Arlequin and MitoTool. Results: Results demonstrated 21 haplotypes distributed among 3 populations with variations between each climate population. In the tropic and sub-tropic populations, the dominant haplotype is h1 while h6 is dominant in the polar population. Conclusions: There is a variation of haplotype polymorphism between tropic, sub-tropic, and polar climate population. &nbsp

Comparing methods for modeling longitudinal and survival data, with consideration of mediation analysis

Joint modeling of longitudinal and survival data has received much attention and is becoming increasingly useful. In clinical studies, longitudinal biomarkers are used to monitor disease progression and to predict survival. These longitudinal measures are often missing at failure times and may be prone to measurement errors. In previous studies these two types of data are frequently analyzed separately where a mixed effects model is used for longitudinal data and a survival model is applied to event outcomes. The argument in favor of a joint model has been the efficient use of the data as the survival information goes into modeling the longitudinal process and vice versa. In this thesis, we present joint maximum likelihood methods, a two stage approach and time dependent covariate methods that link longitudinal data to survival data. First, we use simulation studies to explore and assess the performance of these methods with bias, accuracy and coverage probabilities. Then, we focus on four time dependent methods considering models that are unadjusted and adjusted for time. Finally, we consider mediation analysis for longitudinal and survival data. Mediation analysis is introduced and applied in a research framework based on genetic variants, longitudinal measures and disease risk. We implement accelerated failure time regression using the joint maximum likelihood approach (AFT-joint) and an accelerated failure time regression model using the observed longitudinal measures as time dependent covariates (AFT-observed) to assess the mediated effect. We found that the two stage approach (TSA) performed best at estimating the link parameter. The joint maximum likelihood methods that used the predicted values of the longitudinal measures, similar to the TSA, provided larger estimates. The time dependent covariate methods that used the observed longitudinal measures in the survival analysis underestimated the true estimates. The mediation results showed that the AFT-joint and the AFT-observed underestimated the mediated effect. Comparison of the methods in Framingham Heart Study data revealed similar patterns. We recommend adjusting for time when estimating the association parameter in time dependent Cox and logistic models. Additional work is needed for estimating the mediated effect with longitudinal and survival data

Interferon Production by Nonviral Stimuli of Microbial Origin

An increasing number of nonviral materials of microbial origin has been reported to stimulate the production of interferon in cell cultures and (or) in animals. These materials include (a) gram-negative bacteria or the endotoxins prepared from their cell walls, (b) other microorganisms such as Rickettsiae, Bedsoniae, Protozoa, and (c) fungal products such as a mannan from Candida and various antibiotics which act as protein synthesis inhibitors, e.g., glutarimide antibiotics and tenuazonic acid. A summary is presented of the current state of knowledge about interferon production in animals by the most thoroughly studied nonviral substance of microbial origin, bacterial endotoxin. Further evidence is presented which clearly distinguishes the "endotoxin-type" of interferon response in animals from the response seen after the injection of virus. The data suggest that the release of preformed interferon from the tissues occurs in animals injected with endotoxin. On the other hand, interferon produced in response to the injection of virus is newly synthesized protein. While the exact chemical structure of the component of bacterial endotoxin responsible for interferon release has not yet been elucidated, it is clear that the lipid portion of the lipopolysaccharide, rather than the O-specific polysaccharide side chains or the core polysaccharide, is the active moiety

Tributes

Tributes to Richard V. De Smet and M. M. Thomas

Malawi’s Maize Marketing System

National food security in Malawi depends on improving the performance of maize markets. Ensuring that grain is consistently available at tolerable prices is crucial for consumers’ food security. At the same time, surplus producing farmers need to receive farm-gate prices consistently above production costs to intensify the use of fertilizer and other productivity enhancing technologies in a sustainable manner. These concerns give rise to the classic food price dilemma for policy makers in Malawi: how to keep prices low enough to ensure low income consumers’ access to food while keeping prices high enough to promote farm production incentives. These tensions cannot be avoided but they can be relieved through reducing food marketing margins, which shrink the wedge between producer and consumer prices. Moreover, Malawi faces major political and economic problems associated with food price instability especially given its dependence on rain fed agriculture in a region prone to drought. These issues show that improving the performance of maize markets is at the core of achieving sustainable food security and poverty reduction in Malawi.food security, Malawi, maize, marketing, food policy, Agricultural and Food Policy, Community/Rural/Urban Development, Food Security and Poverty, International Development, Marketing, q12, q18,

Probability Functions for Random Responses: Prediction of Peaks, Fatigue Damage, and Catastrophic Failures

This report reviews a number of theoretical matters in random process theory which can be applied to physical problems such as predicting peaks, structural fatigue damage, and catastrophic structural failures. The presentation emphasizes the basic assumptions which are involved, and discusses how to properly interpret the theoretical results. Various engineering examples are given as illustrations