Collective Motion of Spherical Bacteria

A large variety of motile bacterial species exhibit collective motions while inhabiting liquids or colonizing surfaces. These collective motions are often characterized by coherent dynamic clusters, where hundreds of cells move in correlated whirls and jets. Previously, all species that were known to form such motion had a rod-shaped structure, which enhances the order through steric and hydrodynamic interactions. Here we show that the spherical motile bacteria Serratia marcescens exhibit robust collective dynamics and correlated coherent motion while grown in suspensions. As cells migrate to the upper surface of a drop, they form a monolayer, and move collectively in whirls and jets. At all concentrations, the distribution of the bacterial speed was approximately Rayleigh with an average that depends on concentration in a non-monotonic way. Other dynamical parameters such as vorticity and correlation functions are also analyzed and compared to rod-shaped bacteria from the same strain. Our results demonstrate that self-propelled spherical objects do form complex ordered collective motion. This opens a door for a new perspective on the role of cell aspect ratio and alignment of cells with regards to collective motion in nature.     

Application of NIR Spectroscopy Coupled with PLS Regression for Quantification of Total Polyphenol Contents from the Fruit and Aerial Parts of Citrullus colocynthis

Introduction

Citrullus colocynthis (L.) Schrad is extensively used to treat diabetes, obesity, fever, cancer, amenorrhea, jaundice, leukemia, rheumatism, and respiratory diseases. Chemical studies have indicated the presence of several cucurbitacins, flavones, and other polyphenols in this plant. These phytochemical constituents are responsible for the interesting antioxidant and other biological activities of C. colocynthis.

Objective

In the present study, for the first time, near infrared (NIR) spectroscopy coupled with partial least square (PLS) regression analysis was used to quantify the polyphenolic phytochemicals of C. colocynthis.

Methodology

The fruit and aerial parts of the C. colocynthis were extracted individually in methanol followed by fractionation in n‐hexane, chloroform, ethyl acetate, n‐butanol, and water. Near infrared (NIR) spectra were obtained in absorption mode in the wavelength range 700–2500 nm. The PLS regression model was then built from the obtained spectral data to quantify the total polyphenol contents in the selected plant samples.

Results

The PLS regression model obtained had a R² value of 99% with a 0.98 correlationship value and a good prediction with a root mean square error of prediction (RMSEP) value of 1.89% and correlation of 0.98. These results were further confirmed through UV–vis spectroscopy and it is found that the ethyl acetate fraction has the maximum value for polyphenol contents (101.7 mg/100 g; NIR, 100.4 mg/100 g; UV–vis).

Conclusions

The polyphenolic phytochemicals of the fruit and aerial parts of C. colocynthis have been quantified successfully by using multivariate analysis in a non‐destructive, economical, precise, and highly sensitive method, which uses very simple sample preparation. Copyright © 2017 John Wiley & Sons, Ltd.     

Evolutionary mechanisms underlying the functional divergence of duplicate genes involved in vertebrates' circadian rhythm pathway

Circadian rhythms, that are governed physiologically and behaviorally by endogenous clock, have been described in many species. Living organisms use this endogenous circadian clock to anticipate environmental transitions, perform activities at biologically advantageous times during the day, and undergo characteristic seasonal responses. Gene duplication is one of the most important mechanisms in the evolution of gene diversity. After duplication, one or both of duplicates can accumulate amino acid changes, thereby promoting functional divergence through the action of natural selection. The circadian system, like many other multigene families, has undergone this genetic revolution, and so circadian genes that are found in single copies in insects are duplicated in vertebrates. We analyzed six groups of genes involved in vertebrates' circadian rhythm pathway to find signatures of molecular evolutionary processes such as gene duplication, natural selection, recombination, and functional divergence. The obtained results, then, were used to determine what evolutionary forces have influenced the fates of duplicated genes of each group. We showed in this research that recombination has not been widespread during the evolution of circadian genes and that purifying selection has been the prominent natural pressure operating on circadian genes. We also showed that the evolution of circadian genes has been depended on gene duplication and functional divergence. Finally, we put forward models best describing the evolutionary fates of circadian duplicates.     

The geometry of a synaptic intermediate in a pathway of bacteriophage lambda site-specific recombination.

Bacteriophage lambda uses site-specific recombination to move its DNA into and out of the Escherichia coli genome. The recombination event is mediated by the phage-encoded integrase (Int) at short DNA sequences known as attachment ( att ) sites. Int catalyzes recombination via at least four distinct pathways, distinguishable by their requirements for accessory proteins and by the sequence of their substrates. The simplest recombination reaction catalyzed by Int does not require any accessory proteins and takes place between two attL sites. This reaction proceeds through an intermediate known as the straight-L bimolecular complex (SL-BMC), a stable complex which contains two attL sites synapsed by Int. We have investigated the orientation of the two substrates in the SL-BMC with respect to each other using two independent direct methods, a ligation assay and visualization by atomic force microscopy (AFM). Both show that the two DNA substrates in the complex are arranged in a tetrahedral or nearly square planar alignment skewed towards parallel. The DNA molecules in the complex are bent.     

Development of a coupled modeling for tumor growth,angiogenesis, oxygen delivery,and phenotypic heterogeneity

Biomechanics and Modeling in Mechanobiology - Analysis of the evolution and growth dynamics of tumors is crucial for understanding cancer and the development of individually optimized therapies....