Characterization of xanthans from selected Xanthomonas strains cultivated under constant dissolved oxygen

Seventeen wild-type Xanthomonas isolates were screened in terms of broth viscosity in shake-flasks. As culture conditions affect polymer characteristics, a fair comparison among isolates required their cultivation in a fermenter under controlled dissolved oxygen tension. Three isolates and a reference strain were studied. The mean molecular weights and molecular weight distributions of their xanthans were determined. Products showed different pyruvate (0.2–7%), acetate (5–10%) and proteinaceous nitrogen (1–3%) contents. The selected isolates exhibit properties which could improve xanthan gum production and some could be used to produce polymers with specific characteristics.     

Short Communication: Analysis of effective light in different photobioreactors: its influence on growth,photosynthetic activity and glycerol production by the freshwater green alga Chlamydomonas reinhardtii

The unicellular green alga Chlamydomonas reinhardtii synthesizes glycerol as an osmoregulatory metabolite when exposed to high saline concentrations (200 mM NaCl). Response to osmotic stress can be used for biotechnological production of this compound. When synthesis of a substance is linked to photosynthetic capacity and consequently to effective light, the production on a large scale makes an efficient utilization of light necessary. In the present work a model for evaluation of effective light has been tested.     

Gibberellic acid production using different solid-state fermentation systems

Gibberellic acid production in liquid fermentation was compared with production of this compound in solid-state fermentation systems using cassava flour, sugar cane bagasse and low density polyurethane. Gibberella fujikuroi produced 23 mg of gibberellin/ml in 120h of liquid fermentation. Solid-state fermentation on bagasse showed excellent growth but presented gibberellin extraction problems. Very low production and growth was observed in solid-state fermentation with low density polyurethane as an inert support. Solid-state fermentation on cassava flour showed high production (250 mg/kg of dry solid medium) in a very short time (36h).     

Mixotrophic productivity of the marine diatom Phaeodactylum tricornutum cultured with soluble fractions of rye,wheat and potato

The marine microalga Phaeodactylum tricornutum was cultured semi-continuously with the soluble fractions of wheat, rye and boiled potato flours. Fifteen percent of the culture volume was renewed every 3 d. The cell productivities were 0.9×109 cells/l/d, 1.1×109 cells/l/d and 2.6×109 cells/l/d for wheat, rye and potato respectively. The productivity of the autotrophic control was 1.0×109 cell/l/d. When a soluble fraction of raw potato was added, the productivity was enhanced to 4.1×109 cells/l/d, 2.4 times higher than the autotrophic culture. The high productivity of P. tricornutum with the soluble fractions of Solanum tuberosum suggests its usefulness as a source of nutrients for the production of microalgal biomass.     

Morphological and immunohistochemical study of the midgut and fat body of Spodoptera frugiperda (J.E. Smith) (Lepidoptera: noctuidae) treated with essential oils of the genus Piper

ABSTRACT

Essential oils are a promising alternative to insecticides. We investigated the LD₅₀ of oils extracted from Piper corcovadensis, P. marginatum, and P. arboreum after 48 h topical contact with Spodoptera frugiperda larvae using morphometry, histochemistry and immunohistochemistry of the midgut and fat body. Chromatography revealed that E-caryophyllene was the principal compound common to the Piper species. The essential oils of P. corcovadensis, P. marginatum and P. arboreum caused deleterious changes in the midgut of S. frugiperda larvae. P. corcovadensis oil produced the lowest LD₅₀ and significant histopathological alterations including elongation of the columnar cells, formation of cytoplasmic protrusions, reduction in carbohydrate, increased apoptotic index and decreased cell proliferation. P. arboreum oil caused histopathological alterations similar to P. corcovadensis, but caused the highest rate of cell proliferation and increased regenerative cells, which indicated rapid regeneration of the epithelium. Our findings demonstrated the insecticidal potential of P. corcovadensis for control of S. frugiperda owing to the significant damage it inflicted on S. frugiperda midgut.     

Cell prestress. II. Contribution of microtubules

The tensegritymodel hypothesizes that cytoskeleton-based microtubules (MTs) carrycompression as they balance a portion of cell contractile stress. Totest this hypothesis, we used traction force microscopy to measuretraction at the interface of adhering human airway smooth muscle cellsand a flexible polyacrylamide gel substrate. The prediction is that ifMTs balance a portion of contractile stress, then, upon theirdisruption, the portion of stress balanced by MTs would shift to thesubstrate, thereby causing an increase in traction. Measurements weredone first in maximally activated cells (10 µM histamine) and thenagain after MTs had been disrupted (1 µM colchicine). We found that after disruption of MTs, traction increased on average by ~13%. Because in activated cells colchicine induced neither an increase inintracellular Ca²⁺ nor an increase in myosin light chainphosphorylation as shown previously, we concluded that the observedincrease in traction was a result of load shift from MTs to thesubstrate. In addition, energy stored in the flexible substrate wascalculated as work done by traction on the deformation of thesubstrate. This result was then utilized in an energetic analysis. Weassumed that cytoskeleton-based MTs are slender elastic rods supportedlaterally by intermediate filaments and that MTs buckle as the cellcontracts. Using the post-buckling equilibrium theory of Euler struts,we found that energy stored during buckling of MTs was quantitativelyconsistent with the measured increase in substrate energy afterdisruption of MTs. This is further evidence supporting the idea thatMTs are intracellular compression-bearing elements.

     

APRT from erythrocytes of HGPRT deficient patients: Kinetic,regulatory and thermostability properties

Adenine phosphoribosyltransferase (APRT) has been 1200-fold purified from erythrocytes of a patient with partial hipoxanthine-guanine phosphoribosyltransferase (HGPRT) deficiency, Propositus, and in those of a control^HPRT+, with 20% efficiency in both proteins and specific activity of 550 and 243 nmol/h/mgprotein. The specific activity determined in the Propositus enzyme was, in all purification steps, higher than that of the control^HPRT+. Significant changes were found in their thermal stabilities. Half inactivation times at each temperature studied are greater for the Propositus enzyme in the temperature interval 60–80°C. No significant difference has been observed in the affinity constants for adenine and PRPP substrates. Studies on inhibition by the reaction product suggest that AMP is a competitive inhibitor with respect to PRPP in both enzymes, with K_i values of 150 M in Propositus and 220 M in control^HPRT+.     

Plant endemism in two forests in southern Bahia, Brazil

An important factor in determining species rarity is the geographic distribution of species. Estimates were made of the level of endemism of the flora of two sites in the southern Bahian wet forest zone. Estimates were made for endemism in the Atlantic forest biome and for the much more restricted area of southern Bahia and northern Espi´rito Santo and are derived from analyses of the distributions of the species known from each area. The species checklist for each area is based on identified specimens resulting from intensive collecting in a forest near Serra Grande (40km north of Ilhe´us) and the Una Biological Reserve (40km south of Ilhe´us). Slightly less than half of the species (45.2% at Una and 47.7% at Serra Grande) have widespread distributions and 7.4% at each site are disjunct between the coastal forests and Amazonia. In the Una Reserve, 44.1% of the species are endemic to the coastal forest and 28.1% endemic to southern Bahia and northern Espi´rito Santo. At Serra Grande, 41.6% of the species are endemic to the coastal forest and 26.5% endemic to southern Bahia and northern Espi´rito Santo.     

Sensory Integration Regulating Male Courtship Behavior in Drosophila

The courtship behavior of Drosophila melanogaster serves as an excellent model system to study how complex innate behaviors are controlled by the nervous system. To understand how the underlying neural network controls this behavior, it is not sufficient to unravel its architecture, but also crucial to decipher its logic. By systematic analysis of how variations in sensory inputs alter the courtship behavior of a naïve male in the single-choice courtship paradigm, we derive a model describing the logic of the network that integrates the various sensory stimuli and elicits this complex innate behavior. This approach and the model derived from it distinguish (i) between initiation and maintenance of courtship, (ii) between courtship in daylight and in the dark, where the male uses a scanning strategy to retrieve the decamping female, and (iii) between courtship towards receptive virgin females and mature males. The last distinction demonstrates that sexual orientation of the courting male, in the absence of discriminatory visual cues, depends on the integration of gustatory and behavioral feedback inputs, but not on olfactory signals from the courted animal. The model will complement studies on the connectivity and intrinsic properties of the neurons forming the circuitry that regulates male courtship behavior.     

Placing empirical limits on metapopulation models for terrestrial plants

Both island-biogeographic (dynamic) and niche-based (static) metapopulation models make predictions about the distribution and abundance of species assemblages. We tested the utility of these models concerning such predictions for terrestrial vascular plants using data from 74 landscapes across the globe. We examined correlations between species frequency and local abundance and shapes of the species frequency distribution. No data set met all of the predictions of any single island-biogeographic metapopulation model. In contrast, all data sets met the predictions of the niche-based model. We conclude that in predicting the distribution of species assemblages of plants over scales greater than 10–1 km, niche-based models are robust while current metapopulation models are insufficient. We discuss limitations in the assumptions of the various models and the types of empirical observations that they will each have to deal with in further developments.