Quantification of carbon and phosphorus co-limitation in bacterioplankton: new insights on an old topic

Because the nature of the main resource that limits bacterioplankton (e.g. organic carbon [C] or phosphorus [P]) has biogeochemical implications concerning organic C accumulation in freshwater ecosystems, empirical knowledge is needed concerning how bacteria respond to these two resources, available alone or together. We performed field experiments of resource manipulation (2×2 factorial design, with the addition of C, P, or both combined) in two Mediterranean freshwater ecosystems with contrasting trophic states (oligotrophy vs. eutrophy) and trophic natures (autotrophy vs. heterotrophy, measured as gross primary production:respiration ratio). Overall, the two resources synergistically co-limited bacterioplankton, i.e. the magnitude of the response of bacterial production and abundance to the two resources combined was higher than the additive response in both ecosystems. However, bacteria also responded positively to single P and C additions in the eutrophic ecosystem, but not to single C in the oligotrophic one, consistent with the value of the ratio between bacterial C demand and algal C supply. Accordingly, the trophic nature rather than the trophic state of the ecosystems proves to be a key feature determining the expected types of resource co-limitation of bacteria, as summarized in a proposed theoretical framework. The actual types of co-limitation shifted over time and partially deviated (a lesser degree of synergism) from the theoretical expectations, particularly in the eutrophic ecosystem. These deviations may be explained by extrinsic ecological forces to physiological limitations of bacteria, such as predation, whose role in our experiments is supported by the relationship between the dynamics of bacteria and bacterivores tested by SEMs (structural equation models). Our study, in line with the increasingly recognized role of freshwater ecosystems in the global C cycle, suggests that further attention should be focussed on the biotic interactions that modulate resource co-limitation of bacteria.This research was supported by Junta de Andalucía (Excelencia P09-RNM-5376 to JMMS) and the Spanish Ministry Ciencia e Innovación (CGL2011-23681 to PC)

A comparative study of the mitogenic and morphogenic effects of epidermal growth factor and amphiregulin on colonic carcinoma cells

Available from British Library Document Supply Centre-DSC:DXN031110 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo

Distribution of heterotrophic bacteria as affected by eutrophication and fluctuations of environmental factors

A 21-year time series of heterotrophic bacteria density (CFU on agar plates) at one coastal and one open sea station in the central Adriatic Sea was analysed. A trend of increasing numbers of bacteria was established. A trend-component free spectral analysis of the data showed oscillation periods of 2.3 and 14 years, and 3.5 and 14 years, for the open and coastal sea respectively. Seasonal distribution of heterotrophic bacteria was also analysed for the 1968-1988 period

Bacteria and their distribution under red-tide conditions

Survey of the density of red-tide organisms and bacterioplankton as well as simultaneous determinations of temperature, salinity, pH, secchi disc and dissolved oxygen were carried out at four stations in the Kaštela Bay (middle Adriatic Sea) on a weekly basis between June 15 and September 20, 1989. A close connection between bacterioplankton and Gonyaulax polyedra was observed during the bloom manifested by high coefficients of correlation between them in the surface layers. No correlation was established in the bottom layers since vertical gradients of bacterioplankton density were considerably weaker than in phytoplankton. These differences were also shown in strong vertical gradient of pH and 02-saturation

Epithelial expression and release of FGF-2 from heparan sulphate binding sites in bronchial tissue in asthma

Background: The most characteristic structural change evident in endobronchial biopsies in asthma, even in mild disease, is subepithelial collagen deposition within the lamina reticularis. This has been associated with progressive loss of lung function and the persistence of airway hyperresponsiveness, and has been linked to airway fibroblast proliferation. A potent fibroproliferative factor in bronchoalveolar lavage fluid in asthma is fibroblast growth factor-2 (FGF-2). FGF-2 is a member of a family of heparin binding growth factors that bind to heparan sulphate proteoglycans (HSPG), an important determinant of FGF-2 activity. This study compared the level of expression and distribution of FGF-2 in relation to HSPG in bronchial tissue from normal and asthmatic subjects.Methods: The distribution of FGF-2 and HSPG in intact and cleaved forms in endobronchial biopsies from normal and asthmatic subjects was examined using an immunohistochemical approach. A novel ELISA based method was developed to detect solubilisation of FGF-2 following addition of heparin and heparitinase to bronchial tissue slices.Results: Immunohistochemical analysis showed that FGF-2 was co-localised to HSPG in epithelial and endothelial basement membranes. Epithelial FGF-2, but not HSPG, was significantly more abundant in patients with mild asthma than in normal subjects. In vitro experiments indicated that FGF-2 was released from binding sites in the tissue by heparin and heparitinase I.Conclusions: FGF-2 is bound by HSPG in bronchial tissue. The mast cell, through the release of heparin and endoglycosidase, may make a unique contribution to tissue remodelling in allergic asthma