Characterization of cpsF and its product CMP-N-acetylneuraminic acid synthetase, a group B streptococcal enzyme that can function in K1 capsular polysaccharide biosynthesis in Escherichia coli

Group B Streptococcus (GBS) is the foremost cause of neonatal sepsis and meningitis in the United States. A major virulence factor for GBS is its capsular polysaccharide, a high molecular weight polymer of branched oligosaccharide subunits. N -acetylneuraminic acid (Neu5Ac or sialic acid), at the end of the polysaccharide side chains, is critical to the virulence function of the capsular polysaccharide. Neu5Ac must be activated by CMP-Neu5Ac synthetase before it is incorporated into the polymer. We showed previously that a transposon mutant of a serotype III GBS strain which had no detectable capsular Neu5Ac was deficient in CMP-Neu5Ac-synthetase activity (Wessels et al ., 1992). In this paper, we report the identification and characterization of cpsF , a gene interrupted by transposon insertion in the previously described Neu5Ac-deficient mutant. The predicted amino acid sequence of the cpsF gene product shares 57% similarity and 37% identity with CMP-Neu5Ac synthetase encoded by the Escherichia coli K1 gene, neuA . The enzymatic function of the protein encoded by cpsF was established by cloning the gene in E. coli under the control of the T7 polymerase/promoter. Lysates of E. coli in which the cpsF gene product was expressed, catalysed the condensation of CTP with Neu5Ac to form CMP-Neu5Ac. In addition, when a CMP-Neu5Ac synthetase-deficient mutant of E. coli K1 was transformed with cpsF , K1 antigen expression was restored. We conclude that cpsF encodes CMP-Neu5Ac synthetase in type III GBS, and that the GBS enzyme can function in the capsule-synthesis of a heterologous bacterial species.     

Decrease in tolerance to fenvalerate, in resistantHelicoverpa armigera after pupal diapause

Pyrethroid resistant and susceptible adults ofHelicoverpa armigera (Lepidoptera: Noctuidae) were screened for tolerance to pyrethroids after 6 wk or 12 wk pupal diapuse. Resistant larvae and F₂ larvae from a cross between resistant and susceptible parents (two replicates), were reared under conditions to induce pupal diapause. After eclosion, adults were tested in glass vials coated with the pyrethroid fenvalerate, at a dose (DD) that is known to discriminate between susceptible and heterozygous resistant individuals. In all diapause experiments, the frequency of resistance was lower in the test groups that had experienced diapause compared with the non-diapausing control group. The underlying cause of the decline is not certain but selective mortality of resistant versus susceptible individuals could not account for all the difference in two of the three experiments — tolerance to the pyrethroid, fenvalerate, is most likely to have declined either as a consequence of diapause or from the extended time of development associated with diapause. These results indicate that monitoring programs could underestimate pyrethroid resistance frequencies when usingH. armigera adults emerging from diapause.     

Effects of HCN, phenolic acids and related compounds in Sorghum bicolor on the feeding behaviour of the planthopper Peregrinus maidis

The feeding behaviour of the planthopper Peregrinus maidis was looked at in relation to the cyanide and phenolic compounds found in sorghum. Tests were carried out using both plant material and artificial media. HCN was found to be deterrent in long-term feeding tests with artificial media but it is unlikely to affect feeding when present in the plant. Mixtures of phenolic acids and their esters reduced feeding on artificial media when presented to the insects at concentrations similar to those occurring in young plants. Phenolic acid concentration was correlated with enhanced production of salivary sheath material in both plants and artificial media. In plants high concentrations of phenolic acids were correlated with a reduction in the ability of P. maidis to locate the phloem tissues.

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Résumé Les effets de l'HCN, des acides phénoliques et des composés voisins du Sorgho sur le comportement alimentaire de Peregrinus maidis, ont étré examinés en utilisant la plante ou un régime artificiel. HCN testé dans un régime artificiel est répulsif à des concentrations voisines de celles trouvées dans des plantes de 10 cm de haut. Des tests ultérieurs sur les effects de HCN sur le comportement de pigûre, montrent qu'il est plus toxique que répulsif. Les acides phénoliques et les esters èlevent l'activité perforatrice mais diminuent la prise de nourriture sur régime artificiel. De fortes teneurs en acides phénoliques dans les tissus de la plante sont aussi associées à des piqûres plus longues, à une plus grande ramification des piqûres et à une diminution correspondante de l'aptitude de P. maidis à découvrir le phloeme.

     

Effects of fetal intravenous glucose challenge in normal and growth retarded fetuses

Fetal intravenous glucose challenge test (0.75 g/kg of estimated fetal weight) was performed at 26-33 weeks gestation in 9 patients undergoing fetal blood sampling (FBS) by ultrasound guided needling from the umbilical vein. The indication for FBS was rapid karyotyping for fetal malformations in 5 (control group) and severe intrauterine growth retardation in the remaining 4 (IUGR group). Fetal blood samples were taken before the glucose infusion and after 1, 3, 5, 10 and 15 min; glucose and insulin were assayed on each occasion and acid-base balance at 0 and 5 min. Basal fetal pO2, pH, glucose and insulin were lower in the IUGR group than in controls. Following the glucose challenge, fetal glucose levels were similar in the two groups, but in the IUGR group the latter part of the glucose curve was characterized by a slower and delayed return to basal levels. In control fetuses the insulin response following the glucose challenge peaked at 3 min while in IUGR no change in insulin concentration was detected. Fetal pO2 did not change in either group; the median change in fetal pH was significantly different between the two groups (controls: +0.01; IUGR: -0.04; P less than 0.05) and there was a significant correlation between basal pO2 and the change in fetal pH (r = 0.79) (P less than 0.02). These results support the concept of a low energy state in IUGR. Fetal glucose supplementation in IUGR is unlikely to be of benefit and may even exacerbate underlying acidosis.     

Deep Crustal Communities of the Juan de Fuca Ridge Are Governed by Mineralogy

Volcanic ocean crust contains a global chemosynthetic microbial ecosystem that impacts ocean productivity, seawater chemistry and geochemical cycling. We examined the mineralogical effect on community structure in the aquifer ecosystem by using a four-year in situ colonization experiment with igneous minerals and glasses in Integrated Ocean Drilling Program Hole 1301A on the Juan de Fuca Ridge. Microbial community analysis and scanning electron microscopy revealed that olivine phases and iron-bearing minerals bore communities that were distinct from iron-poor phases. Communities were dominated by Archaeoglobaceae, Clostridia, Thermosipho, Desulforudis and OP1 lineages. Our results suggest that mineralogy determines microbial composition in the subseafloor aquifer ecosystem.     

Using untapped telemetry data to explore the winter biology of freshwater fish

Winter is a challenging period for aquatic research—weather is uncomfortable, ice is hazardous, equipment fails, and daylength is short. Consequently, until recently relatively little research on freshwater fishes has included winter. Telemetry methods for tracking fish and observing movement behavior are an obvious solution to working in harsh conditions because much of the data can be collected remotely, and passive methods collect data year-round without winter maintenance. Yet, many telemetry studies do not collect data during winter or, if they do, only report data from the ice-free seasons while the remaining data are unused. Here, we briefly summarize the advantages and limitations of using telemetry methods in winter, including acoustic and radio telemetry and passive integrated transponder technology, then review the range of questions related to fish ecology, behavior, bioenergetics, and habitat use that can be addressed in winter using telemetry. Our goals are to highlight the untapped potential of winter fish biology and to motivate scientists to revisit their four-season telemetry data and incorporate objectives specific to winter biology in future study plans.