Partenaires et organisations internationales
(Anglais)
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B, CH, D, E, F, GR, H, I, NL, P, S, UK
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Résumé des résultats (Abstract)
(Anglais)
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Hup-hydrogenase activity in light or dark exposed R. rubrum cultures Growth of R. rubrum was followed in cultures kept under anoxic conditions at constant temperature in either continuous light (LL) or continuous darkness (DD). In DD, only small modifications of the turbidity were detected; linear regression analysis nevertheless gives a very significant slope (t(34) = 13.07, p < 10-14, with a R-squared of 0.834). Generation times reflected these differences of growth with12 ± 4.0 h in LL and 43 ± 18.6 h in DD cultures. The uptake hydrogenase (Hup) activity has been followed in situ in whole cells of R. rubrum grown in the same conditions and a clear ultradian rhythm of activity has been observed. Indeed, after about 12 hours in the new media, a rapid rise of hydrogenase activity was observed in both LL and DD cultures after which it decreased again to very low values. The activity of Hup continued to show such fluctuations during the rest of the experiment, both in DD and LL, during the growth and stationary phase. The Lomb-Scargle power periodogram method demonstrates the presence of a clear ultradian rhythmic Hup activity both in LL and DD. In the LL grown cultures, the oscillating activity is faster and continues throughout the growth and the stationary phase, with an ultradian period of 11.7 ± 2.6 h. In DD, the slow growing bacteria showed an ultradian oscillatory pattern of Hup activity with periods of 14.4 ± 1.5 h. The different periods obtained for LL and DD grown bacteria are significantly different. Hup-hydrogenase activity in R. rubrum under different environmental conditions In these experiments it has been shown that factors such as temperature, gas present in the culture, light intensity or light quality also affect the rhythmic oscillations of Hup-hydrogenase activity. These experiments confirmed that the rhythmic behavior belong to the ultradian group. Hup-hydrogenase activity in R. rubrum growing in the presence of selenite R. rubrum was able to grow in the presence of SeO32-. This compound affected the growth, while the end of growing phase was reached around 36 h. after inoculation in the control cultures, it ended only after 58 hours in the presence of 0.5, 1 or 2 mM SeO32-. Generation times of R. rubrum, which are 12.1 h. in the absence of selenite, are 13.7 h., 14.3 h. and 16.3 h. in the cultures containing 0.5, 1 and 2 mM SeO32-, respectively. In the latter cultures, a decrease in optical density (A650) was furthermore observed 4 to 6 hours before the end of the growing lag phase was reached. This drop coincided with the begin of the reduction process, the appearance of volatile selenium in the gas phase and the appearance of absorbency at 420 nm in the total spectrum of selenite grown bacteria. The Hup activity has been followed in-vivo in whole R. rubrum cells. In both the control and the selenite containing cultures, an increase in activity was observed 12 h after inoculation in the fresh media. In the control cultures, the activity of Hup showed regular fluctuations during the whole experiment, while the bacteria were growing, with 'peaks and valleys' periods of 11.6 h. ± 2.7 and 12.1 h. ± 1.1, respectively. Bacteria were growing in the presence of 0.5 mM SeO32-, the hydrogenase activity oscillated (peaks = 11.8 ± 0.9 h, valleys = 12.8 ± 1.7 h), till the moment where SeO32- reduction started. When 1 or 2 mM SeO32- is present, Hup activity fluctuated till the begin of the SeO32- reduction (48 h. after inoculation), a severe drop of activity is then observed. The low level of Hup remains very low is accompanied by a gas overpressure. When hydrogenase activity was followed after addition of glucose or EDTA into the different cultures, the general increase was followed by a general decrease, after which the Hup-hydrogenase activity remained fluctuating. These fluctuations are however less regular, as compared with those observed in control cultures where no compounds were added.
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