A Bioassay for Determining Pathogenicity of Entomogenous Fungi on Whiteflies

A simple and effective laboratory bioassay method for determining the pathogenicity of entomogenous fungi to whiteflies is presented. The bioassay is based on characterization of the growth rate and development of entomogenous fungi on fourth instar nymphs of the silverleaf whitefly (SLWF), Bemisia argentifolii (Bemisia tabaci, Strain B), and is useful in determining the effects of environmental factors (e.g., temperature and humidity) and additives (e.g., surfactants, adjuvants, and pesticides) on the development of entomogenous fungi. Such information can provide a better understanding of the influence of these factors on the performance of entomogenous fungi when tested under field conditions. The bioassay has been successfully implemented for the evaluation of the pathogenicity of Paecilomyces fumosoroseus, Verticillium lecanii, and Beauveria bassiana against fourth instar nymphs of SLWF. It has the potential to be useful as a screening tool for determining pathogenicity of new fungal isolates and for the standardization and quality control of commercial fungal preparations for viability and virulence against insect pests before they are used far field applications.     

Elucidation of trophic interactions in an unusual single-cell nitrogen-fixing symbiosis using metabolic modeling

Marine nitrogen-fixing microorganisms are an important source of fixed nitrogen in oceanic ecosystems. The colonial cyanobacterium Trichodesmium and diatom symbionts were thought to be the primary contributors to oceanic N₂ fixation until the discovery of the unusual uncultivated symbiotic cyanobacterium UCYN-A (Candidatus Atelocyanobacterium thalassa). UCYN-A has atypical metabolic characteristics lacking the oxygen-evolving photosystem II, the tricarboxylic acid cycle, the carbon-fixation enzyme RuBisCo and de novo biosynthetic pathways for a number of amino acids and nucleotides. Therefore, it is obligately symbiotic with its single-celled haptophyte algal host. UCYN-A receives fixed carbon from its host and returns fixed nitrogen, but further insights into this symbiosis are precluded by both UCYN-A and its host being uncultured. In order to investigate how this syntrophy is coordinated, we reconstructed bottom-up genome-scale metabolic models of UCYN-A and its algal partner to explore possible trophic scenarios, focusing on nitrogen fixation and biomass synthesis. Since both partners are uncultivated and only the genome sequence of UCYN-A is available, we used the phylogenetically related Chrysochromulina tobin as a proxy for the host. Through the use of flux balance analysis (FBA), we determined the minimal set of metabolites and biochemical functions that must be shared between the two organisms to ensure viability and growth. We quantitatively investigated the metabolic characteristics that facilitate daytime N₂ fixation in UCYN-A and possible oxygen-scavenging mechanisms needed to create an anaerobic environment to allow nitrogenase to function. This is the first application of an FBA framework to examine the tight metabolic coupling between uncultivated microbes in marine symbiotic communities and provides a roadmap for future efforts focusing on such specialized systems.     

Isolation of protoplasts from sugar beet leaves

Isolated protoplasts were prepared from sugar beet leaves by means of the action of a non-specific enzyme xylonase; homologous fusions and total yield were examined.     

Feeding and locomotor rhythm of the ornamental cichlid fish Amatitlania sp. in different social groups

The aim of this study was to evaluate the feeding activity and the rhythm of daily locomotor activity of the convict cichlid (Amatitlania sp.) kept in different social groups under a self-feeding system. A total of 120 animals was distributed among six repetitions of four social groups, as follows: group 1 with one male and one female per tank; group 2 with three males and three females per tank; group 3 with six males per tank; and group 4 with six females per tank. Feeding activity (FA) and locomotor activity (LA) were evaluated using photoelectric presence-sensors connected to automatic feeders. The fish were fed a commercial extruded diet (46% crude protein and 3600 kcal kg⁻¹ of digestible energy). Animal growth was evaluated for all groups. After 30 days of experimentation, the fish stabilized their demands by adjusting their consumption. Amatitlania sp. showed predominantly diurnal FA and LA. All groups showed a peak of activity when the light was turned on and when it was turned off. In summary, FA and LA of Amatitlania sp. are predominantly diurnal and independent of social group. Pairs and groups of males and females together consume less food in relation to groups of one sex or the other due to reproductive behaviour. On the other hand, groups of only males or females consume more food because they lack reproductive stimuli and thus prioritize growth. These results may support good feeding management practices for this ornamental cichlid. Studies relating feeding behaviour with different social groups are of great importance for determining effective feeding strategies for this species in captivity. Thus, such a study assists in a more efficient production of Amatitlania sp.     

Is the spontaneous motility of isolated rat uterus controlled by prostaglandin E?

Variations in the spontaneous contractile activity during 6 hours following isolation of uterine horns from proestrus, metestrus and spayed rats, were explored. In estrus and metestrus preparations the contractions declined during 60 min and between 180--200 min a progressive spontaneous recovery (abolished by indomethacin) was observed up to 360 min. Uteri from proestrus and spayed animals exhibited a continuous depression without recovery during the whole experimental period. At 60 min, uterine horns from estrus animals (which showed a marked contractile decrement) released to the suspending medium significantly less prostaglandin E-like material than at 360 min, i.e. when contractions had almost completely recovered. No modification in the amount of prostaglandin F-like material was detected accompanying these spontaneous contractile variations. In the spayed group at 60 min of functioning (i.e. when the contractile impairment was significantly smaller than at a later time) the release of PGE was greater than at 360 min. These findings suggest a possible control of rat uterine contractions by PGE, rather than by PGF.     

Localization of nucleic acids in the nucleoli of oocytes and early embryos of mouse and hamster: An autoradiographic study

Mouse preovulatory oocytes, zygotes, parthenogenetically activated pronuclear oocytes, and early embryos, as well as hamster zygotes, were analyzed, by autoradiography, for the distribution of either “maternal” or newly synthesized RNAs. Early mouse embryos were also examined for the distribution of newly replicated DNA. Special attention was attributed to NLBs in oocytes or to NPBs in early embryos. In mouse oocytes, [5-³H]uridine radioactivity accumulated (after a 2-hr pulse) in vitro, in addition to other nuclear compartments, in the central compact material of the NLBs. There was no cytoplasmic labeling. In all parthenogenetic pronuclear embryos developed from similarly labeled oocytes, this label was distinctly detectable in the central compact material of the NPBs; less intensive labeling was seen in the nucleoplasm and cytoplasm. On the contrary, the central compact part of the mouse NPB did not show labeling in DNA after a continuous culture with [6-³H]thymidine. In mouse and hamster pronuclear zygotes, convincing evidence was obtained for a lack of any newly synthesized nucleic acids in the compact material of NPBs using 4- to 10-hr culture with [8-³H]adenosine. Based on these data, it was shown that the NLBs of oocytes or NPBs of early embryos probably contain RNAs synthesized during the last stages of antral follicle oocyte differentiation. This unique pathway of RNAs in the oocyte—embryo system may explain the specific morphology of both oocyte and early embryo “nucleoli.” © 1995 Wiley-Liss, Inc.     

Hydrolysis of a chitosan-induced milk aggregate by pepsin, trypsin and pancreatic lipase.

The addition of chitosan to whole milk results in dose dependent destabilization and coagulation of the casein micelles and milk fat. The present study evaluates how the presence of chitosan could affect the hydrolysis of this chitosan-induced aggregate by different gastrointestinal proteases (pepsin and trypsin) and by pancreatic lipase. The chitosan-milk aggregate was hydrolyzed by pepsin and trypsin, as evaluated by the UV absorbance of TCA-soluble peptides and by urea-PAGE. The kinetics and extent of hydrolysis were independent of the casein being soluble or aggregated. The release of soluble peptides from the aggregate was independent of the presence of chitosan. A progressive inhibition of pancreatic lipase was observed in proportion to the increase in molecular weight of the chitosan employed to induce the formation of the aggregate. Interestingly, the presence of chitosan not only affected the initial velocity of the reaction, but also reduced its extent. The results indicate that a milk aggregate induced by chitosan was very well digested by gastric and intestinal proteases independently of the molecular weight of the chitosan used, and that the aggregate could retain the lipid-lowering effect of chitosan.