Membranes of five-fold alamethicin-resistant<Emphasis Type="Italic">Staphylococcus aureus,Enterococcus faecalis</Emphasis> and<Emphasis Type="Italic">Bacillus cereus</Emphasis> show decreased interactions with alamethicin due to changes in membrane fluidity and surface charge

The aim of this study was to understand development of resistance to alamethicin (a model barrel stave pore forming antimicrobial peptide) by investigating changes in phospholipid profile, fatty acid side chain analysis and extent of alamethicin insertion in biomimetic membrane prepared form wild type strains and five folds alamethicin resistant variants ofStaphylococcus aureus NCDC 110,Enterococcus faecalis NCDC 114 andBacillus cereus NCDC 66. The wild type strains NCDC 110, 114, 66, were sensitive to alamethicin with IC₅₀ 5.5, 3.25 and 2.0 μg/ml respectively. Wild type strains were cultured in the presence of alamethicin to select resistant variants with IC₅₀ 29.0, 17.0 and 9.5 μg/ml respectively. The phospholipid profile analysis revealed increase in amino-group containing phospholipids to amino-group lacking phospholipids ratio between wild-type and resistant variant inS. aureus and B. cereus but decreased inE. faecalis. Predominant fatty acids in all strains were composed of even number of carbons. Linoleic acid was detected only in resistant strain ofB. cereus. As indicated by saturated-to-unsaturated fatty acids ratio, the membrane fromS. aureus andE. faecalis became more rigid, whereas, inB. cereus it became more fluid. Using a colorimetricin vitro assay, a decrease in alamethicin insertion in the biomimetic membrane could be observed upon acquisition of resistance. The membranes of five-fold alamethicin-resistantS. aureus, E. faecalis andB. cereus revealed changes in membrane fluidity and surface charge upon acquisition of resistance to alamethicin.     

Unfolding of the chromatin fiber driven by overexpression of noninteracting bridging factors

Nuclear molecules control the functional properties of the chromatin fiber by shaping its morphological properties. The biophysical mechanisms controlling how bridging molecules compactify chromatin are a matter of debate. On the one side, bridging molecules could cross-link faraway sites and fold the fiber through the formation of loops. Interacting bridging molecules could also mediate long-range attractions by first tagging different locations of the fiber and then undergoing microphase separation. Using a coarse-grained model and Monte Carlo simulations, we study the conditions leading to compact configurations both for interacting and noninteracting bridging molecules. In the second case, we report on an unfolding transition at high densities of the bridging molecules. We clarify how this transition, which disappears for interacting bridging molecules, is universal and controlled by entropic terms. In general, chains are more compact in the case of interacting bridging molecules because interactions are not valence limited. However, this result is conditional on the ability of our simulation methodology to relax the system toward its ground state. In particular, we clarify how, unless using reaction dynamics that change the length of a loop in a single step, the system is prone to remain trapped in metastable, compact configurations featuring long loops.     

Association of interleukin-18 genotypes (−607C > A) and (−137 G > C) with the hepatitis B virus disease progression to hepatocellular carcinoma

Chronic infection with HBV has been reported to be associated with the development of HCC. The inflammation mounted by cytokine-mediated immune system plays an important role in the pathogenesis of HBV-associated HCC. IL-18 is a pro-inflammatory cytokine whose role in the development of HBV-associated chronic to malignant disease state has not been much studied. The present study was conceived to determine the role of genetic polymorphisms in IL-18, serum levels of IL-18, and expression level of its signal transducers in the HBV disease progression. A total of 403 subjects were enrolled for this study including 102 healthy subjects and 301 patients with HBV infection in different diseased categories. Polymorphism was determined using PCR–RFLP. Genotypic distributions between the groups were compared using odd’s ratio and 95% CI were calculated to express the relative risk. Circulating IL-18 levels were determined by ELISA. Expression levels of pSTAT-1 and pNF?B was determined by western blotting. In case of IL-18(??607C?>?A), the heterozygous genotype (CA) was found to be a protective factor while in case of IL-18(??137G?>?C) the heterozygous genotype (GC) acted as a risk factor for disease progression from HBV to HCC. Moreover, serum IL-18 levels were significantly increased during HBV disease progression to HCC as compared to controls. Also the levels of activated signal transducers (pSTAT-1 and pNF-κB) of IL-18 in stimulated PBMCs were significantly increased during HBV to HCC disease progression. These findings suggest that IL-18 has the potential to act as a biomarker of HBV-related disease progression to HCC.

     

Pathogenicity of Colletotrichum gloeosporioides (Penz.) Sacc. causal agent of anthracnose in different varieties of eggplant (Solanum melongena L.) determined by levels of cross-reactive antigens shared by host and pathogen

Pathogenicity test of the fungal pathogen Colletotrichum gloeosporioides (Penz.) Sacc., causal agent for anthracnose in eggplant (Solanum melongena L.), was performed in 28 commercially cultivated eggplant varieties by analysing the antigenic patterns of host and pathogen. Through initial screening following detached leaf inoculation technique and whole plant inoculation technique, Pusa purple long (Ppl) variety was found to be the most susceptible while Shamala variety (Shav) was the most resistant. Cross-reactive antigens (CRA) shared by susceptible varieties and C. gloeosporioides was detected by immunodiffusion and immunoelectrophoresis and indirect enzyme-linked immunosorbent assay (ELISA). Such antigens could not be detected between the resistant varieties and the pathogen and also between a nonpathogen (Alternaria porri) and all the test varieties. However, ELISA showed that low levels of common antigens were present between all combinations. The level of CRA was found to decrease with increasing resistance. Indirect immunogold labeling followed by silver enhancement revealed that CRA were concentrated mainly in the cell wall regions throughout the tissue. The level of CRA was found to correlate to the pathogenicity of C. gloeosporioides in different eggplant varieties. ELISA may therefore be used to screen the commercially cultivated eggplant varieties for resistance to C. gloeosporioides.     

Biochemical changes and adaptive strategies of plants under heavy metal stress

Heavy metal contamination of soil, aqueous waste stream and ground water causes major environmental and human health problems. Heavy metals are major environmental pollutants when they are present in high concentration in soil and show potential toxic effects on growth and development in plants. Due to unabated, indiscriminate and uncontrolled discharge of hazardous chemicals including heavy metals into the environment, plant continuously have to face various environmental constraints. In plants, seed germination is the first exchange interface with the surrounding medium and has been considered as highly sensitive to environmental changes. One of the crucial events during seed germination entails mobilization of seed reserves which is indispensable for the growth of embryonic axis. But, metabolic alterations by heavy metal exposure are known to depress the mobilization and utilization of reserve food by affecting the activity of hydrolytic enzymes. Some plants possess a range of potential mechanisms that may be involved in the detoxification of heavy metals by which they manage to survive under metal stress. High tolerance to heavy metal toxicity could rely either on reduced uptake or increase planned internal sequestration which is manifested by an interaction between a genotype and its environment. Such mechanism involves the binding of heavy metals to cell wall, immobilization, exclusion of the plasma membrane, efflux of these toxic metal ions, reduction of heavy metal transport, compartmentalization and metal chelation by tonoplast located transporters and expression of more general stress response mechanisms such as stress proteins. It is important to understand the toxicity response of plant to heavy metals so that we can utilize appropriate plant species in the rehabilitation of contaminated areas. Therefore, in the present review attempts have been made to evaluate the effects of increasing level of heavy metal in soils on the key behavior of hydrolytic and nitrogen assimilation enzymes. Additionally, it also provides a broad overview of the strategies adopted by plants against heavy metal stress.     

Thermostable hexameric form of Eis (Rv2416c) protein of M. tuberculosis plays an important role for enhanced intracellular survival within macrophages

Eis protein is reported to enhance the intracellular survival of Mycobacterium tuberculosis in human macrophages. Eis protein is not only known to skew away the immunity by disturbing the protective T(H)1 response, but aminoglycoside acetyltransferase activity of Eis is reported to regulate autophagy, inflammation and cell death. Here we have gained insight into the structure-function properties of Eis. Eis protein is a hexameric αβ protein. Although urea and guanidinium hydrochloride (GdmCl) was found to induce one-step unfolding of Eis but size exclusion chromatography showed that GdmCl treated Eis maintained its hexameric form. SDS-PAGE assay confirmed that hexameric form of Eis is partially stable to SDS and converts into trimers and monomers. Out of these three forms, aminoglycoside acetyltransferase activity is found to be associated only with hexamers. The Tm of Eis was found to be ～75°C. Aminoglycoside acetyltransferase Eis demonstrated remarkable heat stability retaining >80% of their activity at 70°C which falls down to ～50% at 75°C and is completely inactive at 80°C. Further, intracellular survival assay with heated samples of M. smegmatis harboring eis gene of M. tuberculosis H37Rv demonstrated a possible role for the thermostability associated with Eis protein in the enhanced intracellular survival within macrophages. In sum, these data reveal that only hexameric form of Eis has a thermostable aminoglycoside acetyltransferase activity. This is the first report showing the thermostability associated with aminoglycoside acetyltransferase activity of Eis protein being one of the essential features for the execution of its biological role.