Carbon flows in eutrophic Lake Rotsee: a <Superscript>13</Superscript>C-labelling experiment

The microbial segment of food webs plays a crucial role in lacustrine food-web functioning and carbon transfer, thereby influencing carbon storage and CO₂ emission and uptake in freshwater environments. Variability in microbial carbon processing (autotrophic and heterotrophic production and respiration based on glucose) with depth was investigated in eutrophic, methane-rich Lake Rotsee, Switzerland. In June 2011, ¹³C-labelling experiments were carried out at six depth intervals in the water column under ambient light as well as dark conditions to evaluate the relative importance of (chemo)autotrophic, mixotrophic and heterotrophic production. Label incorporation rates of phospholipid-derived fatty acid (PLFA) biomarkers allowed us to differentiate between microbial producers and calculate group-specific production. We conclude that at 6 m, net primary production (NPP) rates were highest, dominated by algal photoautotrophic production. At 10 m —the base of the oxycline— a distinct low-light community was able to fix inorganic carbon, while in the hypolimnion, heterotrophic production prevailed. At 2 m depth, high label incorporation into POC could only be traced to nonspecific PLFA, which prevented definite identification, but suggests cyanobacteria as dominating organisms. There was also depth zonation in extracellular carbon release and heterotrophic bacterial growth on recently fixed carbon. Large differences were observed between concentrations and label incorporation of POC and biomarkers, with large pools of inactive biomass settling in the hypolimnion, suggesting late-/post-bloom conditions. Net primary production (115 mmol C m^?2 d^?1) reached highest values in the epilimnion and was higher than glucose-based production (3.3 mmol C m^?2 d^?1, highest rates in the hypolimnion) and respiration (5.9 mmol C m^?2 d^?1, highest rates in the epilimnion). Hence, eutrophic Lake Rotsee was net autotrophic during our experiments, potentially storing large amounts of carbon.     

Parasite accessory cell interactions in murine leishmaniasis. I. Evasion and stimulus-dependent suppression of the macrophage interleukin 1 response by Leishmania donovani

Interleukin 1 (IL 1) is a principal mediator of the host immune response to microbial challenge. Accessory cells of the monocyte-macrophage series are a major source of this cytokine and are also chronically parasitized by protozoa of the genus Leishmania. This suggests that characterization of the macrophage IL 1 response to Leishmania would increase our understanding of the regulation of host immunity to these organisms. In the present study, the macrophage IL 1 response to Leishmania donovani was examined because infections with this organism have findings consistent with parasite-specific T cell unresponsiveness. Cytokine activity was measured either by direct stimulation or by co-stimulation of thymocytes. Conditioned media from BALB/c resident peritoneal macrophages infected with amastigotes of L. donovani contained no more IL 1 than did supernatant fluids of control cells. In contrast, supernatants from cells stimulated with lipopolysaccharide or heat-killed Listeria monocytogenes had significantly increased cytokine content. Resident cells infected with L. donovani for 4 hr before being stimulated with Listeria demonstrated a suppressed IL 1 response (approximately 40% of Listeria alone) to this secondary particulate stimulus. In contrast, the secondary response of leishmania-preinfected cells to lipopolysaccharide was not affected. To examine whether accessory cell nonresponsiveness to L. donovani (with respect to IL 1) was related to the state of macrophage activation, elicited peritoneal macrophages obtained by injection of proteose peptone were also studied. These cells responded to stimulation with lipopolysaccharide and fixed Staphylococcus aureus with increases in intracellular, membrane, and secreted cytokine activities. In contrast, L. donovani failed to induce any of these activities. This was found to be the case irrespective of whether amastigotes were alive or killed or opsonized with specific antibodies. Elicited cells preinfected with Leishmania responded normally to secondary stimulation with lipopolysaccharide, but not S. aureus (64% of Staphylococcus alone). In addition, attachment and penetration of L. donovani promastigotes and their subsequent conversion to amastigotes within macrophages failed to induce IL 1 synthesis. The findings of this study indicate that L. donovani has the ability to both evade and suppress the macrophage IL 1 response. Because this monokine provides an obligatory signal during macrophage-dependent T cell activation, evasion of signal transduction for IL 1 synthesis may be related to defects in cell-mediated immunity which occur during infections with this organism.     

Gabaergic Pharmacological Activity of Propofol Related Compounds as Possible Enhancers of General Anesthetics and Interaction with Membranes

Phenol compounds, such as propofol and thymol, have been shown to act on the GABA_A receptor through interaction with specific sites of this receptor. In addition, considering the high lipophilicity of phenols, it is possible that their pharmacological activity may also be the result of the interaction of phenol molecules with the surrounding lipid molecules, modulating the supramolecular organization of the receptor environment. Thus, in the present study, we study the pharmacological activity of some propofol- and thymol-related phenols on the native GABA_A receptor using primary cultures of cortical neurons and investigate the effects of these compounds on the micro viscosity of artificial membranes by means of fluorescence anisotropy. The phenol compounds analyzed in this article are carvacrol, chlorothymol, and eugenol. All compounds were able to enhance the binding of [³H]flunitrazepam with EC₅₀ values in the micromolar range and to increase the GABA-evoked Cl^? influx in a concentration-dependent manner, both effects being inhibited by the competitive GABA_A antagonist bicuculline. These results strongly suggest that the phenols studied are positive allosteric modulators of this receptor. Chlorothymol showed a bell-type effect, reducing its positive effect at concentrations >100 μM. The concentrations necessary to induce positive allosteric modulation of GABA_A receptor were not cytotoxic. Although all compounds were able to decrease the micro viscosity of artificial membranes, chlorothymol displayed a larger effect which could explain its effects on [³H]flunitrazepam binding and on cell viability at high concentrations. Finally, it is suggested that these compounds may exert depressant activity on the central nervous system and potentiate the effects of general anesthetics.     

CHROMOSOME NUMBERS OF CAMPANULACEAE. II. THE LOBELIA TUPA COMPLEX OF CHILE

Gametic chromosome numbers are reported for 27 collections representing the four species of the Lobelia tupa complex (Campanulaceae, Lobelioideae) in Chile; all are n = 21. This represents the first report of chromosome numbers for L. bridgesii Hook. & Arn., L. excelsa Bonpl., and L. polyphylla Hook. & Arn., and confirms previous reports of this number in L. tupa L. As the basic chromosome number of Lobelioideae is x = 7, these species are interpreted as hexaploids. Higher polyploids are extremely rare among Lobelioideae; most of those previously reported have been either sporadic individuals or populations within an otherwise diploid or tetraploid species, or occasional species within an otherwise diploid and tetraploid lineage. This is the first report of an entire complex of lobelioid species that is uniformly hexaploid. This suggests that the Chilean endemics are relatively derived within Lobelia, and offers some support for the monophyly of the complex.