137 research outputs found
Preliminary Characterization of Extracellular Allelochemicals of the Toxic Marine Dinoflagellate Alexandrium tamarense Using a Rhodomonas salina Bioassay
Members of the marine dinoflagellate genus Alexandrium are known to exude allelochemicals, unrelated to well-known neurotoxins (PSP-toxins, spirolides), with negative effects on other phytoplankton and marine grazers. Physico/chemical characterization of extracellular lytic compounds of A. tamarense, quantified by Rhodomonas salina bioassay, showed that the lytic activity, and hence presumably the compounds were stable over wide ranges of temperatures and pH and were refractory to bacterial degradation. Two distinct lytic fractions were collected by reversed-phase solid-phase extraction. The more hydrophilic fraction accounted for about 2% of the whole lytic activity of the A. tamarense culture supernatant, while the less hydrophilic one accounted for about 98% of activity. Although temporal stability of the compounds is high, substantial losses were evident during purification. Lytic activity was best removed from aqueous phase with chloroform-methanol (3:1). A “pseudo-loss” of lytic activity in undisturbed and low-concentrated samples and high activity of an emulsion between aqueous and n-hexane phase after liquid-liquid partition are strong evidence for the presence of amphipathic compounds. Lytic activity in the early fraction of gel permeation chromatography and lack of activity after 5 kD ultrafiltration indicate that the lytic agents form large aggregates or macromolecular complexes
No Effect of Microgravity and Simulated Mars Gravity on Final Bacterial Cell Concentrations on the International Space Station: Applications to Space Bioproduction
Microorganisms perform countless tasks on Earth and they are expected to be essential
for human space exploration. Despite the interest in the responses of bacteria to space
conditions, the findings on the effects of microgravity have been contradictory, while
the effects of Martian gravity are nearly unknown. We performed the ESA BioRock
experiment on the International Space Station to study microbe-mineral interactions in
microgravity, simulated Mars gravity and simulated Earth gravity, as well as in ground
gravity controls, with three bacterial species: Sphingomonas desiccabilis, Bacillus
subtilis, and Cupriavidus metallidurans. To our knowledge, this was the first experiment
to study simulated Martian gravity on bacteria using a space platform. Here, we tested
the hypothesis that different gravity regimens can influence the final cell concentrations
achieved after a multi-week period in space. Despite the different sedimentation rates
predicted, we found no significant differences in final cell counts and optical densities
between the three gravity regimens on the ISS. This suggests that possible gravityrelated effects on bacterial growth were overcome by the end of the experiment. The
results indicate that microbial-supported bioproduction and life support systems can be
effectively performed in space (e.g., Mars), as on Earth
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