Nanosilica synthesis mediated by Aspergillus parasiticus strain

Rice husks (RHs) are plant waste materials abundant in phytoliths silica bodies. These were used as starting material for fungal-mediated biotransformation leading to the synthesis of a high-value added product. A strain of Aspergillus parasiticus was capable of transforming the amorphous silica conglomerates into structured nanoparticles (NPs) in the process of RHs biotransformation. Silica NPs were produced extracellularly and their size ranged from 3 to 400 nm depending on the biotransformation conditions and the post-biotransformation supernatant processing. To characterize the NP's structure and dimension, SEM, STEM, EDX and FTIR technics were applied. These demonstrated and confirmed that pyramid (400 nm), cubical (85 nm) and spherical (3 nm and 24 ± 8 nm) forms of silica NPs were obtained.     

Mother-to-infant transmission of human immunodeficiency virus type 1 involving five envelope sequence subtypes.

Genetic analysis of human immunodeficiency virus type 1 (HIV-1) from cases of mother-to-infant transmission were analyzed in an effort to provide insights into the viral selection that may occur during transmission, as well as the timing and source of transmitted viruses. HIV-1 env genes obtained from seven mothers and their perinatally infected infants in Sweden were studied. Five envelope sequence clades (A to E) were found to be represented. We used a heteroduplex tracking assay (HTA) to assess the genetic relatedness between early viral isolates from the infants and serial maternal virus populations taken during pregnancy and at delivery. HTA findings were used to select for DNA sequence analysis maternal virus populations that were either closely or more distantly related to the infant virus. In each case, nucleotide sequence analysis confirmed the genetic relationships inferred by the HTA. Only maternal peripheral blood was sampled, and large sets of maternal specimens throughout pregnancy were generally not available. However, no consistent correlation was found to support the hypothesis that infant viruses should match blood-derived maternal virus genotypes found early in pregnancy if infants were found to be infected at birth or, conversely, that infant viruses should match blood-derived maternal virus genotypes found at delivery if infants were found to be infected only some time later.     

SPECIATION AND POPULATION GENETIC STRUCTURE IN TROPICAL PACIFIC SEA URCHINS

Unlike populations of many terrestrial species, marine populations often are not separated by obvious, permanent barriers to gene flow. When species have high dispersal potential and few barriers to gene flow, allopatric divergence is slow. Nevertheless, many marine species are of recent origin, even in taxa with high dispersal potential. To understand the relationship between genetic structure and recent species formation in high dispersal taxa, we examined population genetic structure among four species of sea urchins in the tropical Indo-West Pacific that have speciated within the past one to three million years. Despite high potential for gene flow, mtDNA sequence variation among 200 individuals of four species in the urchin genus Echinometra shows a signal of strong geographic effects. These effects include (1) substantial population heterogeneity; (2) lower genetic variation in peripheral populations; and (3) isolation by distance. These geographic patterns are especially strong across scales of 5000-10,000 km, and are weaker over scales of 2500-5000 km. As a result, strong geographic patterns would not have been readily visible except over the wide expanse of the tropical Pacific. Surface currents in the Pacific do not explain patterns of gene flow any better than do patterns of simple spatial proximity. Finally, populations of each species tend to group into large mtDNA regions with similar mtDNA haplotypes, but these regional boundaries are not concordant in different species. These results show that all four species have accumulated mtDNA differences over similar spatial and temporal scales but that the precise geographic pattern of genetic differentiation varies for each species. These geographic patterns appear much less deterministic than in other well-known coastal marine systems and may be driven by chance and historical accident.     

Regulation of guanylate cyclase activity by atrial natriuretic factor and protein kinase C

Summary The putative second messenger of certain atrial natriuretic factor (ANF) signal transductions is cyclic GMP. Recently, we purified a 180-kDa protein, apparently containing both ANF receptor and guanylate cyclase activities, and hypothesized that this is one of the cyclic GMP transmembrane signal transducers. The enzyme is ubiquitous and appears to be conserved. Utilizing the 180-kDa membrane guanylate cyclase, we now show that the 180-kDa guanylate cyclase is regulated in opposing fashions by two receptor signals—ANF stimulating it and protein kinase C inhibiting it. Furthermore, protein kinase C phosphorylates the 180-kDa enzyme. This suggests a novel switch on and switch off mechanism of the cyclic GMP signal transduction. Switch off represents the phosphorylation while switch on the dephosphorylation of the enzyme.     

A new anaerobic bacterium,forming up to five endospores per cell —Anaerobacter polyendosporus gen. et spec. nov.

An obligately anaerobic sporeforming bacterium assigned to a new genus and species Anaerobacter polyendosporus gen. et spec. nov. is described. Characteristic features distinguishing the bacterium from known anaerobic sporeformers were variable cell shape, including spherical, the ability to form up to five endospores per cell, diffusive distribution of reserve polysaccharide throughout the cytoplasm, independence from growth factors. The eubacterial nature of the organism was revealed by its sensitivity to 1 mg/l of streptomycin, rifampicin, penicillin and to lysozyme. It belonged to Firmicutes by the type of cell wall structure. The cell wall consisted of one layer; the outer membrane was absent. The cells were not motile. The spores were spherical or oval, heat-resistant, contained dipicolinic acid and had typical endospore structure. Cortex, coats, spore coare, and in most cases exosporium could be distinguished. The bacterium fermented carbohydrates, but not amino acids. The products of fermentation included ethanol, acetate, lactate, butyrate, butanol, H₂ and CO₂. Sulfate or nitrate could not be used as electron acceptors, but nitrite was reduced to NH ₄ ⁺ in a dissimilatory process. The bacterium was capable of fixing N₂. The G + C content of the DNA was 29 mol %. The bacterium was isolated from meadow-gley soil.     

Positive and negative control of nod gene expression in Rhizobium meliloti is required for optimal nodulation

We show that expression of common nodulation genes in Rhizobium meliloti is under positive as well as negative control. A repressor protein was found to be involved in the negative control of nod gene expression. Whereas the activator NodD protein binds to the conserved cis-regulatory element (nod-box) required for coordinated regulation of nod genes, the repressor binds to the overlapping nodD1 and nodA promoters, at the RNA polymerase binding site. A model depicting the possible interaction of the plant-derived nod gene inducer (luteolin), the NodD and the repressor with the nod promoter elements is presented. Mutants lacking the repressor exhibited delayed nodulation phenotype, indicating that fine tuning of nod gene expression is required for optimal nodulation of the plant host.