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Gas Vesicles (gas + vesicle)
Selected AbstractsGlucose inhibits the formation of gas vesicles in Haloferax volcanii transformantsENVIRONMENTAL MICROBIOLOGY, Issue 1 2008Torsten Hechler Summary The effect of glucose on the formation of gas vesicles was investigated in Haloferax mediterranei and Hfx.volcanii transformants containing the mc- gvp gene cluster of Hfx. mediterranei (mc-vac transformants). Increasing amounts of glucose in the medium resulted in a successive decrease in the amount of gas vesicles in both species, with a complete inhibition of their formation at glucose concentrations of > 70 mM in mc-vac transformants, and 100 mM in Hfx. mediterranei. Maltose and sucrose imposed a similar inhibitory effect, whereas xylose, arabinose, lactose, pyruvate and 2-deoxy-glucose had no influence on the gas vesicle formation in mc-vac transformants. The activities of the two mc-vac promoters were strongly reduced in mc-vac transformants grown in the presence of > 50 mM glucose. The gas vesicle overproducing ,D transformant (lacking the repressing protein GvpD) also showed a glucose-induced lack of gas vesicles, indicating that GvpD is not involved in the repression. The addition of glucose was useful to block gas vesicle formation at a certain stage during growth, and vice versa, gas vesicle synthesis could be induced when a glucose-grown culture was shifted to medium lacking glucose. Both procedures will enable the investigation of defined stages during gas vesicle formation. [source] SEDIMENTARY IMPRINT OF MICROCYSTIS AERUGINOSA (CYANOBACTERIA) BLOOMS IN GRANGENT RESERVOIR (LOIRE, FRANCE),JOURNAL OF PHYCOLOGY, Issue 3 2007Delphine Latour Analysis of a sediment core taken from the Grangent reservoir in 2004 showed the presence of high concentrations of Microcystis aeruginosa Kütz. colonies at the sediment surface (250 colonies,ˇ,mL sediment,1) and also at depths of 25,35 cm (2300 coloniesˇmL sediment,1) and 70 cm (600 colonies,ˇ,mL sediment,1). Measurements of radioactive isotopes (7Be, 137Cs, and 241Am) along with photographic analysis of the core were used to date the deep layers: the layer located at ,30 cm dates from summer 2003, and that located at ,70 cm from 1990 to 1991. The physiological and morphological conditions of those benthic colonies were compared with those of planktonic colonies using several techniques (environmental scanning electron microscopy [ESEM], TEM, DNA markers, cellular esterases, and toxins). The ESEM observations showed that, as these colonies age, peripheral cells disappear, with no cells remaining in the mucilage of the deepest colonies (70 cm), an indication of the survival thresholds of these organisms. In the benthic phase, the physiological conditions (enzyme activity, cell division, and intracellular toxins) and ultrastructure (particularly the gas vesicles) of the cells surviving in the heart of the colony are comparable to those of the planktonic form, with all the potential needed for growth. Maintaining cellular integrity requires a process that can provide sufficient energy and is expressed in the reduced, but still existing, enzymatic activity that we measured, which is equivalent to a quiescent state. [source] Anaerobiosis inhibits gas vesicle formation in halophilic ArchaeaMOLECULAR MICROBIOLOGY, Issue 1 2009Torsten Hechler Summary The effect of anaerobiosis on the gas vesicle formation was investigated in three Halobacterium salinarum strains, Haloferax mediterranei and in Haloferax volcanii transformants. All these strains significantly reduced gas vesicle formation or lacked these structures under anoxic conditions. When grown by arginine fermentation, Hbt. salinarum PHH4 lacked gas vesicles, whereas Hbt. salinarum PHH1 and NRC-1 contained 5,20 small gas vesicles arranged in two to three aggregates per cell instead of the 30,80 gas vesicles present under oxic conditions. The enlargement presumably stopped due to a depletion of Gvp proteins. Also Hfx. mediterranei and Hfx. volcanii transformants lacked gas vesicles under anoxic growth and yielded a 10-fold reduced gvp transcription. Even the gas vesicle-overproducing ,D transformants did not form gas vesicles under anoxic conditions, demonstrating that the repressing protein GvpD was not involved. The presence of large amounts of GvpA implied that the assembly of the gas vesicles was inhibited. When Hbt. salinarum PHH1 and NRC-1 were grown with dimethyl sulphoxide or trimethylamine N -oxid under anoxic conditions the number but not the size of gas vesicles was reduced. This was in contrast to the previously reported overproduction of gas vesicles in NRC-1 that turned out to depend on the citrate-containing medium used for growth. [source] | ||||||||||