External membrane vesicles from Helicobacter pylori induce apoptosis in gastric epithelial cells

The Helicobacter pylori infection of gastric mucosa is one of the most common infectious diseases and is associated with a variety of clinical outcomes, including peptic ulcer disease and gastric cancer. Helicobacter pylori-induced damage to gastric mucosal cells is controlled by bacterial virulence factors, which include VacA and CagA. Outer membrane vesicles are constantly shed by the bacteria and can provide an additional mechanism for pathogenicity by releasing non-secretable factors which can then interact with epithelial cells. The present report shows that external membrane vesicles are able to induce apoptosis not mediated by mitochondrial pathway in gastric (AGS) epithelial cells, as demonstrated by the lack of cytochrome c release with an activation of caspase 8 and 3. Apoptosis induced by these vesicles does not require a classic VacA+ phenotype, as a negative strain with a truncated and therefore non-secretable form of this protein can also induce cell death. These results should be taken into account in future studies of H. pylori pathogenicity in strains apparently VacA-.     

Preservation of Xanthomonas campestris on agar slopes: effects on xanthan production

Xanthomonas campestris NRRL B-1459 and a variant E2, when preserved on agar slopes (transferred monthly) over 11 months did not deteriorate in their ability to produce xanthan in quantity and quality, as determined by culture in 500-ml baffled flasks. Variations between 8 and 14% (with respect to the average) in the final xanthan concentration were observed for the E2 and B-1459 strains, respectively. A wide range of final viscosities was obtained; these were consistent with the changes in gum concentration. Differences were more likely associated with differences in fermentation kinetics rather than being inherent to the strains. The rheological quality of both polysacharides was relatively constant throughout the time of culture maintenance. Preservation of these bacteria on agar slopes was an adequate method, in contrast to previous reports. In the period studied, strain E2 produced higher gum titres and slightly lower gum quality compared to strain B-1459. Correspondence to: E. Galindo     

Local adaptation: simultaneously considering herbivores and their host plants

? Although a major expectation of coevolutionary theory between plants and herbivores is the occurrence of reciprocal local adaptation, this has remained almost untested. Thus, we evaluated the presence and variation in the patterns of reciprocal local adaptation between an herbivorous insect and its host plant. ? Two four-by-four cross-infestation experiments were performed under similar abiotic conditions. The first one was done under laboratory conditions to estimate herbivore individual performance while the second one was performed in a common garden to simultaneously estimate herbivore population growth rate as well as seed production and plant defenses (resistance and tolerance to herbivory). ? The patterns of population differentiation for the herbivore and the plant were not independent of each other, showing all the possible outcomes from locally adapted to maladapted populations. These results indicate differences in the magnitude of local adaptation. While an association between resistance and herbivore performance was observed, there was no clear pattern between tolerance and herbivore local adaptation. ? Our results demonstrated the occurrence of reciprocal local adaptation following the pattern expected by theory: when the herbivores or the plants were adapted, the other species was non-adapted or even maladapted.     

Phytoplankton dynamics in a deep, tropical, hyposaline lake

The annual variation of the phytoplankton assemblage of deep (64.6 m), hyposaline (8.5 g l^–1) Lake Alchichica, central Mexico (19 ° N, 97° W), was analyzed in relation to thermal regime, and nutrients concentrations. Lake Alchichica is warm monomictic with a 3-month circulation period during the dry, cold season. During the stratified period in the warm, wet season, the hypolimnion became anoxic. N–NH₃ ranged between non detectable (n.d.) and 0.98 mg l^–1, N–NO₂ between n.d. and 0.007 mg l^–1, N–NO₃ from 0.1 to 1.0 mg l^–1 and P–PO₄ from n.d. to 0.54 mg l^–1. Highest nutrient concentrations were found in the circulation period. Chlorophyll a varied from <1 to 19.8 g l^–1 but most values were <5 g l^–1. The euphotic zone (>1% PAR) usually comprised the top 15–20 m. Nineteen algae species were identified, most of them are typical inhabitants of salt lakes. Diatoms showed the highest species number (10) but the small chlorophyte Monoraphidium minutum, the single-cell cyanobacteria, Synechocystis aquatilis, and the colonial chlorophyte, Oocystis parva, were the numerical dominant species over the annual cycle. Chlorophytes, small cyanobacteria and diatoms dominated in the circulation period producing a bloom comparable to the spring bloom in temperate lakes. At the end of the circulation and at the beginning of stratification periods, the presence of a bloom of the nitrogen-fixing cyanobacteria, N. spumigena, indicated nitrogen-deficit conditions. The well-stratified season was characterized by low epilimnetic nutrients levels and the dominance of small single-cell cyanobacteria and colonial chlorophytes. Phytoplankton dynamics in tropical Lake Alchichica is similar to the pattern observed in some deep, hyposaline, North American temperate lakes.