Biofiltration of reduced sulphur compounds and community analysis of sulphur-oxidizing bacteria

The present work aims to use a two-stage biotrickling filters for simultaneous treatment of hydrogen sulphide (H₂S), methyl mercaptan (MM), dimethyl sulphide (DMS) and dimethyl disulphide (DMDS). The first biofilter was inoculated with Acidithiobacillus thiooxidans (BAT) and the second one with Thiobacillus thioparus (BTT). For separate feeds of reduced sulphur compounds (RSC), the elimination capacity (EC) order was DMDS > DMS > MM. The EC values were 9.8 g_MM-S/m³/h (BTT; 78% removal efficiency (RE); empty bed residence time (EBRT) 58 s), 36 g_DMDS-S/m³/h (BTT; 94.4% RE; EBRT 76 s) and 57.5 g_H2S-S/m³/h (BAT; 92% RE; EBRT 59 s). For the simultaneous removal of RSC in BTT, an increase in the H₂S concentration from 23 to 293 ppmv (EBRT of 59 s) inhibited the RE of DMS (97-84% RE), DMDS (86-76% RE) and MM (83-67% RE). In the two-stage biofiltration, the RE did not decrease on increasing the H₂S concentration from 75 to 432 ppmv.     

Viral genome segmentation can result from a trade-off between genetic content and particle stability

The evolutionary benefit of viral genome segmentation is a classical, yet unsolved question in evolutionary biology and RNA genetics. Theoretical studies anticipated that replication of shorter RNA segments could provide a replicative advantage over standard size genomes. However, this question has remained elusive to experimentalists because of the lack of a proper viral model system. Here we present a study with a stable segmented bipartite RNA virus and its ancestor non-segmented counterpart, in an identical genomic nucleotide sequence context. Results of RNA replication, protein expression, competition experiments, and inactivation of infectious particles point to a non-replicative trait, the particle stability, as the main driver of fitness gain of segmented genomes. Accordingly, measurements of the volume occupation of the genome inside viral capsids indicate that packaging shorter genomes involves a relaxation of the packaging density that is energetically favourable. The empirical observations are used to design a computational model that predicts the existence of a critical multiplicity of infection for domination of segmented over standard types. Our experiments suggest that viral segmented genomes may have arisen as a molecular solution for the trade-off between genome length and particle stability. Genome segmentation allows maximizing the genetic content without the detrimental effect in stability derived from incresing genome length.     

Combined effects of chlorpromazine and high fat diet on lipid levels and enzyme activities in bile, liver and plasma of Wistar rats

The effects of high fat diet and injection of chlorpromazine on bile lipid secretion were studied in the rats fed a control diet (C), a saturated fat, high cholesterol diet (S) and a polyunsaturated fat, high cholesterol diet (PU). As compared to controls, injection of chlorpromazine in the S and PU diet groups caused no appreciable change in the level of bile salts and bile phospholipids. Chlorpromazine did however enhance bile cholesterol, especially in the PU group, and lower secretion of lysosomal enzyme (beta-glucuronidase) into bile. Impairment of lysosomal enzyme secretion but not of bile lipid secretion suggests that the lysosomal activity is not directly involved in the bile secretion mechanism. These data point up the risks of using chlorpromazine therapy in association with a diet high in fat and cholesterol.     

Nucleotide sequence heterogeneity of the RNA from a natural population of foot-and-mouth-disease virus

The genomic RNA from isolates of foot-and-mouth-disease virus (FMDV) of serological types O or C obtained during epizootic outbreaks have been analysed by two-dimensional gel electrophoresis of the T1 RNase-generated oligonucleotides (T1 fingerprinting). Among virus isolates that are closely related serologically, 4-12 oligonucleotide changes were detected constitute the genome, the variations affect 0.7%-2.2% positions in FMDV RNA. Higher nucleotide-sequence divergence exists between the genomic RNAs from serologically unrelated viruses, while a 100-fold lower RNA sequence heterogeneity has been detected by analysis of individual clones derived from one viral isolate. Oligonucleotide mapping indicates that the variant oligonucleotides are scattered throughout the FMDV genome. We suggest that extensive genetic variability at many RNA sites is the basis for the antigenic diversity of FMDV.     

Characterization of the human transferrin receptor produced in a baculovirus expression system

Recombinant human transferrin receptor has been produced in a baculovirus expression system. Magnetic particles coated with an anti-transferrin receptor monoclonal antibody were used to immunoselect virus-infected Sf9 insect cells expressing the human transferrin receptor on their cell surface. Recombinant virus containing the human transferrin receptor cDNA was then plaque-purified from these cells. Biosynthetic labeling studies of infected cells showed that the human transferrin receptor is one of the major proteins made 2-3 days postinfection. The recombinant receptor made in insect cells is glycosylated and is also posttranslationally modified by the addition of a fatty acid moiety. However, studies with tunicamycin and endoglycosidases H and F showed that the oligosaccharides displayed on the recombinant receptor differ from those found on the naturally occurring receptor in human cells. As a consequence, the human receptor produced in the baculovirus system has an Mr of 82,000 and is smaller in size than the authentic receptor. About 30% of human transferrin receptors made in insect cells do not form intermolecular disulfide bonds, but are recognized by the anti-transferrin receptor antibody, B3/25, and bind specifically to a human transferrin-Sepharose column. Binding studies using 125I-labeled human transferrin showed that insect cells infected with the recombinant virus expressed an average of 5.8 +/- 0.9 X 10(5) transferrin receptors (Kd = 63 +/- 9 nM) on their cell surface. Thus, the human transferrin receptor produced in insect cells is biologically active and appears suitable for structural and functional studies.     

A rare fraction of human hematopoietic stem cells with large telomeres

The lack of specific markers for stem cells makes the physical identification of this compartment difficult. Hematopoietic stem cells differ in their repopulating and self-renewal potential. Our study shows that multiple classes of human hematopoietic CD34+ greatly differ in telomere length. Flow-cytometry-based fluorescent in situ hybridization and confocal microscopy of CD34+ cells has revealed remarkable telomere length heterogeneity, with a hybridization pattern consistent with different classes of human hematopoietic progenitor cells. These results also point to the existence of a significant clonal heterogeneity among primitive hematopoietic cells and provide the first evidence of a rare fraction of CD34+ cells with large telomeres in humans. Marta García-Escarp and Vanessa Martinez-Muñoz contributed equally to this work.This work was supported by a grant to J.P. from the Spanish Ministry of Science and Technology (SAF2002-02618) and by a grant to V.M.-M. from DakoCytomation.     

Carbohydrate Depletion in Roots and Leaves of Salt-Stressed Potted <Emphasis Type="Italic">Citrus clementina</Emphasis> L.

In citrus, damage produced by salinity is mostly due to toxic ion accumulation, since this salt-sensitive crop adjusts osmotically with high efficiency. In spite of this observation, the putative role of sugars as osmolites under salinity remains unknown. In this work, we have studied carbohydrate contents (total hexoses, sucrose and starch) in leaves and roots of citrus grown under increasing salinity. The experimental system was characterized through the analyses of several parameters known to be strongly affected by salinity in citrus, such as chloride accumulation, photosynthetic rate, ethylene production and leaf abscission. Three-year-old plants of the Clementina de Nules cultivar grafted on Carrizo citrange rootstock were watered with three different levels of salinity (NaCl was added to the watering solutions to achieve final concentrations of 30, 60 and 90 mM). Data indicate that salt stress caused an accumulation of chloride ions in a way proportional to the external increase in NaCl. The adverse conditions reduced CO₂ assimilation, increased ethylene production and triggered abscission of the injured leaves. Data also show that salinity induced progressive depletions of carbohydrates in leaves and roots of citrus plants. This observation clearly indicates that sugar accumulation is not a main component of the osmotic adjustment machinery in citrus.     

Hydrogenase genes are uncommon and highly conserved in Rhizobium leguminosarum bv. viciae

A screening for hydrogen uptake (hup) genes in Rhizobium leguminosarum bv. viciae isolates from different locations within Spain identified no Hup+ strains, confirming the scarcity of the Hup trait in R. leguminosarum. However, five new Hup+ strains were isolated from Ni-rich soils from Italy and Germany. The hup gene variability was studied in these strains and in six available strains isolated from North America. Sequence analysis of three regions within the hup cluster showed an unusually high conservation among strains, with only 0.5-0.6% polymorphic sites, suggesting that R. leguminosarum acquired hup genes de novo in a very recent event.