Influence of host cultivars and Rhizobium species on the growth and symbiotic performance of Phaseolus vulgaris under salt stress

In order to study the effect of salt stress on the Rhizobium-common bean symbiosis, we investigated the response of both partners, separately and in symbiosis. The comparison of the behaviour of five cultivars of Phaseolus vulgaris differing in seed colour, growing on nitrates and different concentrations of NaCl, showed genotypic variation with respect to salt tolerance. Coco Blanc was the most sensitive cultivar, whereas SMV 29-21 was the most tolerant one. At the Rhizobium level, two strains previously selected for their salt tolerance were used: Rhizobium tropici strain RP163 and Rhizobium giardinii strain RP161. Their relative growth was moderately decreased at 250mM NaCl, but they were able to grow at a low rate in the presence of 342 mM NaCl. Their viability at the minimal inhibitory concentration was slightly affected. The effect of salinity on Rhizobium-plant association was studied by using the tolerant variety SMV 29-21 and the sensitive one Coco Blanc inoculated separately with both strains. In the absence of salinity, the strains induced a significantly higher number of nodules on the roots of the cultivar SMV 29-21 compared to those of Coco Blanc. Concerning effectiveness, both strains were similarly effective with SMV 29-21, but not with Coco Blanc. In the presence of salinity, Coco Blanc was more severely affected when associated with RP163 than with RP161. Salinity affected the nodulation development more than it affected the infection steps. Neither of the two strains was able to nodulate SMV 29-21 under saline conditions, in spite of the fact that this was considered the most salt-tolerant variety. The unsuccessful nodulation of SMV 29-21 could be related to the inhibition by salt of one or more steps of the early events of the infection process. In conclusion, N-fixing plants were found to be more sensitive to salt stress than those depending on mineral nitrogen. Evidence presented here suggests that a best symbiotic N2 fixation under salinity conditions could be achieved if both symbiotic partners, as well as the different steps of their interaction (early events, nodule formation, activity, etc.), are all tolerant to this stress.     

Use of a homologous radioimmunoassay (RIA) to evaluate the effect of maternal and foetal parameters on pregnancy-associated glycoprotein (PAG) concentrations in sheep

Early pregnancy detection and prediction of the number of lambs would be profitable for sheep breeders because it enables them to adjust nourishment of pregnant ewes according to the individual needs in order to prevent health problems around parturition. The concentration of ovPAG has previously been reported to be related with maternal parameters (farm, breed and age) as well as foetal parameters (number of lambs, their sex and birth weight), but contradictory results were obtained in different small-scale studies. This large-scale study evaluates the effect of these parameters on the ovPAG concentration, determined by a homologous radioimmunoassay (RIA), and it further investigates the possibility to predict the number of lambs by means of homologous ovPAG determination. Eighty-three and ninety-five ewes of the Suffolk and Texel breed, respectively, housed on four different farms (experiment 1) and 68 ewes of the Suffolk breed, housed on two different farms (experiment 2) were included in this study, and their estrous cycles were synchronised using a progesterone analogue. On the day of synchronisation (D-14) and at 25 (D25), 35 (D35) and 45 (D45) days after insemination, blood samples were taken and a homologous radioimmunoassay (RIA) was used to determine the ovPAG concentrations. At parturition, age of the ewe, number and sex of the lambs (experiment 1) and birth weight (experiment 2) were registered. OvPAG concentrations were not affected by age of the ewe and sex of the lambs. Farm and breed of the ewes, number and birth weight of the lambs had a significant effect on ovPAG concentrations at all time points (P<0.05). The odds of multiple lambs increased significantly with increasing ovPAG concentration, although prediction of litter size based on ovPAG concentration at the individual ewe level was not useful due to small sensitivity and/or specificity whatever the cutoff value used. In conclusion, the ovPAG concentration is affected by farm and breed of the ewes, and number and birth weight of the lambs.     

Gene expression between a congenic strain that contains a quantitative trait locus of high bone density from CAST/EiJ and its wild-type strain C57BL/6J

Peak bone density is an important determining factor of future osteoporosis risk. We previously identified a quantitative trait locus (QTL) that contributes significantly to high bone density on mouse chromosome 1 from a cross between C57BL/6J (B6) and CAST/EiJ (CAST) mouse strains. We then generated a congenic strain, B6.CAST-1T, in which the chromosomal fragment containing this QTL had been transferred from CAST to the B6 background. The congenic mice have a significantly higher bone density than the B6 mice. In this study we performed cDNA microarray analysis to evaluate the gene expression profile that might yield insights into the mechanisms controlling the high bone density by this QTL. This study led to several interesting observations. First, approximately 60% of 8,734 gene accessions on GEM I chips were expressed in the femur of B6 mice. The expression and function of two-thirds of these expressed genes and ESTs have not been documented previously. Second, expression levels of genes related to bone formation were lower in congenic than in B6 mice. These data are consistent with a low bone formation in the congenic mice, a possibility that is confirmed by reduced skeletal alkaline phosphatase activity in serum compared with B6 mice. Third, expression levels of genes that might have negative regulatory action on bone resorption were higher in congenic than in B6 mice. Together these findings suggest that the congenic mice might have a lower bone turnover rate than B6 mice and raise the possibility that the high bone density in the congenic mice could be due to reduced bone resorption rather than increased bone formation. Electronic Publication     

Double radial immunodiffusion as a tool to identify pregnancy-associated glycoproteins in ruminant and nonruminant placentae

Pregnancy-associated glycoproteins (PAGs) are antigens synthesized in the superficial layers of the ruminant trophoblast. Initially, they were identified either as proteins released into the maternal bloodstream (where they have applications in pregnancy diagnosis) (PAG1) or as molecules binding to the LH receptor (PAG2). In this study, double radial immunodiffusion was used to test the ability of antisera raised against different PAG molecules (bovine, ovine and caprine) to react with placental extracts from nonruminants (rabbit, cat, mouse, pig, and wild pig) and ruminants (cow, ewe, and goat). Placental extracts from all nonruminants tested except rabbit reacted with anti bovine PAG2 (anti-boPAG2). Extracts of ruminant placentas reacted with different antisera, confirming the expression of various PAG molecules. According to the time at which the placentas were collected (early or middle pregnancy), the reaction differed as regards the thickness, position, and number of precipitation lines, suggesting that PAG expression varies as pregnancy progresses. Bos indicus and Bos taurus placental extracts exhibited different reactions with anti-boPAG2: a single precipitation line in the former case and two lines in the latter. This suggests differential expression of boPAG2 related glycoproteins in these two subspecies.     

CXCR4-dependent infection of CD8+, but not CD4+, lymphocytes by a primary human immunodeficiency virus type 1 isolate

We recently isolated from an infant an X4-syncytium-inducing (SI) human immunodeficiency virus type 1 (HIV-1) variant (92US143-T8) that was able to infect CD8+ lymphocytes independently of CD4. Although it was CD4 independent, the 92US143-T8 isolate also maintained the ability to infect CD4+ cells. In the present study, we investigated the role of CXCR4 in the infection of CD4+ and CD8+ cells by this primary isolate. The expression of CXCR4 was down modulated in CD8+ lymphocytes after infection with the 93US143-T8 isolate. Infection of CD8+ lymphocytes by the 93US143-T8 isolate was prevented by treatment with AMD3100, a specific antagonist for CXCR4, indicating CXCR4-dependent infection. Interestingly, AMD3100 treatment had no inhibitory role in the infection of purified CD4+ lymphocytes by the same isolate. Furthermore, AMD3100 treatment failed to prevent infection of known CD4+ CXCR4+ T-cell lines (MT-2 and CEM) by the 93US143-T8 isolate. In fact, virus replication in the CD4+ cells was often enhanced in the presence of AMD3100. Viruses produced from the infected CD4+ cells in the presence of AMD3100 maintained an unchanged envelope genotype and an SI phenotype. For the first time, these results provide evidence of CXCR4-dependent infection of CD8+ lymphocytes by a primary HIV-1 isolate. This study also shows a different mode of infection for the CD4+ and CD8+ lymphocytes by the same HIV-1 variant. Finally, our findings suggest that a more careful evaluation is necessary before the random use of AMD3100 as a new entry inhibitor in patients harboring SI HIV-1 strains.     

Isolation of CD4-independent primary human immunodeficiency virus type 1 isolates that are syncytium inducing and acutely cytopathic for CD8+ lymphocytes

Previous studies have established the existence of CD4-independent simian immunodeficiency virus, human immunodeficiency virus type 2 (HIV-2), and laboratory strains of HIV-1. However, whether CD4-independent viruses may also exist in HIV-1-infected patients has remained unclear. We have recently reported the isolation of viruses from an AIDS patient that were able to infect CD8(+) cells independent of CD4, using CD8 as a receptor. Using a similar approach, here we examined viruses from 12 randomly selected patients (obtained from the AIDS Research and Reference Program, National Institutes of Health) for the presence of CD4-independent HIV-1. CD4-independent variants were isolated from infected CD8(+) cells from the viral quasispecies of 7 of 12 patients. The CD4-independent isolates were able to infect primary CD8(+) cells as well as a CD4(-) CD8(+) T-cell line. Soluble CD4 and blocking anti-CD4 or -CD8 antibody had no effect on infection of CD8(+) cells. Remarkably, two of the seven CD4-independent isolates, but not their parental bulk viruses, induced syncytia and caused acute death of infected CD8(+) cells. Some of the CD4-independent variants were also able to infect U87 cells that were negative for CD4, CD8, and common HIV coreceptors, suggesting a novel entry mechanism for these isolates. The CD4-independent isolates were derived from adults and children infected with subtypes A, B, and D. Although no common motif for CD4 independence was found, novel sequence changes were observed in critical areas of the envelopes of the CD4-independent viruses. These results demonstrate that HIV-1-infected patients can frequently harbor viruses that are able to mediate CD4-independent infection of CD8(+) cells. In addition, this study also provides evidence of primary HIV-1 variants that are syncytium inducing and acutely cytopathic for CD8(+) lymphocytes.     

Caffeoyl coenzyme A O-methyltransferase down-regulation is associated with modifications in lignin and cell-wall architecture in flax secondary xylem

Caffeoyl coenzyme A O-methyltransferase (CCoAOMT, EC 2.1.1.104) down-regulated-flax (Linum usitatissimum) plants were generated using an antisense strategy and functionally characterized. Chemical analyses (acetyl bromide and thioacidolysis) revealed that the lignin quantity was reduced and that the Syringyl/Guaïacyl (S/G) lignin monomer ratio was modified in the non-condensed lignin fraction of two independent down-regulated lines. These modifications were associated with altered xylem organization (both lines), reduced cell-wall thickness (one line) and the appearance of an irregular xylem (irx) phenotype (both lines). In addition UV microspectroscopy also indicated that CCoAOMT down-regulation induced changes in xylem cell-wall structure and the lignin fractions. Microscopic examination also suggested that CCoAOMT down-regulation could influence individual xylem cell size and identity. As a first step towards investigating the cellular mechanisms responsible for the unusual structure of flax lignin (G-rich, condensed), recombinant flax CCoAOMT protein was produced and its affinity for different potential substrates evaluated. Results indicated that the preferred substrate was caffeoyl coenzyme A, followed by 5-hydroxyconiferaldehyde suggesting that flax CCoAOMT possesses a small, but probably significant 5′ methylating activity, in addition to a more usual 3′ methylating activity.     

Characteristics and Dynamics of Salmonella Contamination along the Coast of Agadir,Morocco

The occurrence of Salmonella enterica in the environment of tropical and desert regions has remained largely uninvestigated in many areas of the world, including Africa. In the present study, we investigated the presence of Salmonella spp. along 122 km of the coastline of Agadir (southern Morocco) in relation to environmental parameters. A total of 801 samples of seawater (243), marine sediment (279), and mussels (279) were collected from six sites between July 2004 and May 2008. The overall prevalence of Salmonella spp. was 7.1%, with the highest occurrence in mussels (10%), followed by sediment (6.8%) and seawater (4.1%). Only three serotypes were identified among the 57 Salmonella sp. strains isolated. S. enterica serotype Blockley represented 43.8% of all Salmonella strains and was identified in mussel and sediment samples. S. enterica serotype Kentucky (29.8%) was found almost exclusively in mussels, whereas S. enterica serotype Senftenberg (26.3%) was detected in sediment and seawater. Statistical analysis using generalized additive models identified seawater temperature, environmental temperature, rainfall, and solar radiation as significant factors associated with the presence of Salmonella. Rainfall was the only variable showing a linear positive effect on the presence of Salmonella in the sea, whereas the remaining variables showed more complex nonlinear effects. Twenty-eight (49.1%) Salmonella isolates displayed resistance to ampicillin (22 isolates), nalidixic acid (9 isolates), sulfonamide compounds (2 isolates), and tetracycline (1 isolate), with six of these isolates displaying multiple resistance to two of these antimicrobial agents. Pulsed-field gel electrophoresis analysis revealed homogenous restriction patterns within each serotype that were uncorrelated with the resistance pattern profiles.Salmonella enterica bacteria are one of the most frequent causes of food-borne infections transmitted to humans, mainly from animal products (9). In addition to health concerns, the presence of Salmonella contamination in the food chain has serious economic consequences related to the costs of medical care and lost productivity (36). Thus, studies aimed at examining the capacity of Salmonella spp. to survive in different habitats are critical for controlling contamination and understanding the routes of colonization of new hosts (40).Salmonella bacteria display a high degree of resistance to a large variety of stress factors, which provides them with an enhanced capacity to persist in changing environments (40). However, the persistence of the organism outside of the host is not uniform among the different serogroups (3, 4, 13, 24, 32, 34). About 50 of the more than 2,500 different serotypes of Salmonella included in the current classification scheme (29) are dominantly identified in human and animal sources (34). Information about groups that predominate in a given environment and their relationship to potential human or animal origins remains scarce. In recent years, some studies carried out in aquatic environments have provided new insights into the ecological preferences of different Salmonella serogroups in these environments. These studies have revealed the presence of specific patterns of contamination in different geographical areas in association with environmental and oceanographic variables (13, 24, 32) and have identified major factors and conditions that favor the presence of the contaminating bacteria. Identification of the different Salmonella strains present in the environment at serotype level is an essential preliminary step in discriminating potentially clinically important strains among the Salmonella present in contaminated areas, providing invaluable information about the nature of the contamination and allowing the inference of potential routes of dissemination through microbial source tracking (31). All of this information is critical for an improved assessment of the potential risks to public health associated with Salmonella and for the evaluation of the ecological preferences of the diverse and heterogeneous group of organisms which comprise the genus Salmonella (26).The lack of information regarding the epidemiology, contamination, and potential routes of transmission of Salmonella is of particular concern in many regions of the world, such as Africa and Central America, where gastrointestinal diseases continue to be a major cause of illness, primarily due to poor sanitary conditions and nutritional deficiencies. In the present study, we investigated the dynamics of Salmonella contamination in the coastal areas of Agadir, a populous region of southern Morocco where shellfish production and maritime tourism are important to the local economy. Information concerning the biological characteristics of the isolates was correlated with environmental data in order to evaluate the climatic conditions that favor contamination of this region by this pathogen and to identify the potential sources of contamination.     

Changes in ecdysteroid and juvenile hormone levels in developing eggs of Bombyx mori

It is well-known that insect eggs can contain very high concentrations of ecdysteroids, which undergo drastic changes during embryogenesis. We found that this is equally valid for juvenile hormones. Three juvenile hormone-immunoreactive compounds were observed in developing Bombyx mori eggs. They were assumed to be juvenile hormones 1, 2 and 3 according to their retention time in HPLC. These hormones underwent drastic and sudden changes. In the space of one day their concentration was seen to rise rapidly from an undetectable level up to as high as 4 × 10^?6 micromoles per mg of eggs. Their presence was detected as early as the first day of embryonic development, as well as during the blastokinesis period (day 5 to day 9) and in late embryos (day 12 to day 14). Their relative concentrations varied greatly. On two occasions, day 1 and day 8, all three hormones were simultaneously present. Moreover, juvenile hormone 3 was present during the blastokinesis period, either alone or in combination with hormone 2. The latter was the only hormone present in late embryos, before hatching. Thus, with regard to both ecdysteroids (ecdysone and 20-hydroxyecdysone) and juvenile hormones, each day of embryonic development displayed a different hormonal pattern. These patterns undoubtedly constitute a “hormonal code” of embryogenesis control. While 20-hydroxyecdysone can be assumed to trigger cuticulogenesis in embryos as it does in larvae, the effects of the other hormones as well as their possible interactions are questionable.     

Quantitative study and modelling of the litter decomposition in a European alluvial forest. Is there an influence of overstorey tree species on the decomposition of ivy litter (Hedera helix L.)?

The influence on the decomposition rate of ivy litter (Hedera helix L.) of three ligneous overstorey species (oak, Quercus robur L., white poplar, Populus alba and ash, Fraxinus excelsior L.) that support ivy was studied in an alluvial hardwood forest. The ivy provides an abundant litter at the end of spring. The decomposition of ivy litter and the nutrient release rate were analyzed over four months during the growing season of the canopy trees, the hypothesis being that throughfall could slow down the mass loss rate of ivy depending on the support species. Mathematical models for mass loss and nutrient (P, N, K and Mg) release rates were developed. Mass loss rate and the release rate of magnesium, nitrogen and phosphorus show significant differences depending on species whereas no influence of species was observed on the release rate of potassium. The results illustrate the significant effect of oak compared to ash and poplar in slowing down mass loss rate and nitrogen, phosphorus and magnesium release rates. The mass loss rate over time under the three species followed the proposed exponential model, whereas the release rates of phosphorus and magnesium did not follow this model. This model is fitted to the data in two cases out of three for potassium. Magnesium and potassium are released more rapidly when nitrogen accumulates and the phosphorus content does not change significantly. No species × date interaction was observed, except in the case of magnesium. The species effect is interpreted as an effect of composition of throughfalls and presence or absence of inhibitory substances such as phenolic compounds.