Two gene clusters co-ordinate for a functional N-acetylglucosamine catabolic pathway in Vibrio cholerae.

Pathogenic microorganisms like Vibrio cholerae are capable of adapting to diverse living conditions, especially when they transit from their environmental reservoirs to human host. V. cholerae attaches to N-acetylglucosamine (GlcNAc) residues in glycoproteins and lipids present in the intestinal epithelium and chitinous surface of zoo-phytoplanktons in the aquatic environment for its survival and colonization. GlcNAc utilization thus appears to be important for the pathogen to reach sufficient titres in the intestine for producing clinical symptoms of cholera. We report here the involvement of a second cluster of genes working in combination with the classical genes of GlcNAc catabolism, suggesting the occurrence of a novel variant of the process of biochemical conversion of GlcNAc to Fructose-6-phosphate as has been described in other organisms. Colonization was severely attenuated in mutants that were incapable of utilizing GlcNAc. It was also shown that N-acetylglucosamine specific repressor (NagC) performs a dual role - while the classical GlcNAc catabolic genes are under its negative control, the genes belonging to the second cluster are positively regulated by it. Further application of tandem affinity purification to NagC revealed its interaction with a novel partner. Our results provide a genetic program that probably enables V. cholerae to successfully utilize amino - sugars and also highlights a new mode of transcriptional regulation, not described in this organism.

Atomistic simulation studies of magnetite surface structures and adsorption behavior in the presence of molecular and dissociated water and formic acid.

Static energy minimization techniques have been used to elucidate the surface structures of magnetite crystals in pure and hydroxylated forms. Adsorption energy values in the presence of molecular water, dissociate water and simple carboxylic group molecule (formic acid) are calculated and we found that the carboxylic group do not adsorb strongly in most of the pure and hydroxylated surfaces in comparison to water. Since the associated calcium minerals are floated from magnetite using fatty acid collector, our calculations corroborate the flotation practice of removing these impurity minerals from magnetite.

Competitive adsorption on wollastonite: an atomistic simulation approach.

Atomistic simulation techniques are used to simulate surface structure and adsorption behavior of scarcely floatable wollastonite mineral in the presence of molecular and dissociated water, methanoic acid, and methylamine. The latter two additives represent the two widely used collector head-group molecules. The static energy minimization code METADISE was used to perform the simulation to obtain pure surface energy and adsorption energy in the presence of added molecule. The hydroxylation was performed on those surfaces where low-coordinated silicon was made to saturate by bonding with hydroxyl group, and the subsequent charge neutralization was maintained by adding proton on single-coordinated surface oxygen. A comparison of surface energies revealed that all the surfaces become stabilized in the presence of added molecules; however, the presence of methylamine decreased the surface energy to lower values. Adsorption of dissociated water is preferred by the {100} and {102} surfaces, whereas the {001} surface preferred methylamine adsorption, because these show highly negative adsorption energies. In terms of molecular adsorption, the preferred adsorption sequence for all the surfaces is methylamine > methanoic acid > water without considering coadsorption. For the {100} and {102} surfaces, the adsorption energy values of carboxylic acid and amine are more negative than that of water and therefore we conclude that both carboxyl and amine head-group molecules adsorb preferably on wollastonite. Our simulation verify usability of carboxylic acid head group as widely used collectors for wollastonite flotation and, at the same time, it predicts the use of amine head-group collectors as possible modifiers, which corresponds well with our experimental findings.

Analysis of different approaches for evaluation of surface energy of microbial cells by contact angle goniometry.

Microbial adhesion on solid substrate is important in various fields of science. Mineral-microbe interactions alter the surface chemistry of the minerals and the adhesion of the bacterial cells to mineral surface is a prerequisite in several biobeneficiation processes. Apart from the surface charge and hydrophobic or hydrophilic character of the bacterial cells, the surface energy is a very important parameter influencing their adhesion on solid surfaces. There were many thermodynamic approaches in the literature to evaluate the cells surface energy. Although contact angle measurements with different liquids with known surface tension forms the basis in the calculation of the value of surface energy of solids, the results are different depending on the approach followed. In the present study, the surface energy of 140 bacterial and seven yeast cell surfaces has been studied following Fowkes, Equation of state, Geometric mean and Lifshitz-van der Waals acid-base (LW-AB) approaches. Two independent issues were addressed separately in our analysis. At first, the surface energy and the different components of the surface energy for microbial cells surface are examined. Secondly, the different approaches are evaluated for their internal consistency, similarities and dissimilarities. The Lifshitz-van der Waals component of surface energy for most of the microbial cells is realised to be approximately 40 mJ/m2 +/-10%. Equation of state and Geometric mean approaches do not possess any internal consistency and yield different results. The internal consistency of the LW-AB approach could be checked only by varying the apolar liquid and it evaluates coherent surface energy parameters by doing so. The electron-donor surface energy component remains exactly the same with the change of apolar liquid. This parameter could differentiate between the Gram-positive and Gram-negative bacterial cells. Gram-negative bacterial cells having higher electron-donor parameter had lower nitrogen, oxygen and phosphorous content on their cell surfaces. Among the four approaches, LW-AB was found to give the most consistent results. This approach provides more detailed information about the microbial cell surface and the electron-donor parameter differentiates different type of cell surfaces.

Morphology and histology of the female reprodutive system of Abedus ovatus Stal (Belostomatidae: Hemiptera: Insecta)

In Abedus ovatus Stal, the female reprodutive system consists of a pair of ovaries leading to oviduct and opens out by genital aperture. Each ovary is composed of five telotrophic ovarioles, with four different regions, terminal filament, germarium, vitellarium and pedicel. Germarium and vitellarium are the germ tubes in which the development of oocyte occurs. In the germarium, the differentiation of trophocytes into young oocytes was observed in three zones, Z I, Z II and Z III. Further development of oocytes in the vitellarium could be divided into seven stages, ST I-ST VII. The development eggs are lodged in the pedicel.