4a). The measuring chamber is thermostat controlled by a water jacket, and the liquid is continuously mixed by a magnetic stirrer. Light can be applied by a fiber optic illuminator (e.g., from Schott, Mainz, Germany; www.​schott.​com) (more detailed descriptions of the setup are given in references, Jouanneau et al. 1980; Lindberg et al. 2004). Fig. 4 a Schematic #click here randurls[1|1|,|CHEM1|]# of a measuring chamber connected to the vacuum of an MS as is set-up in the CEA Cadarache. An aliquot (ca. 1.5 ml) of the algal suspension is injected into

the measuring chamber of the Hansatech type where it is stirred by a little stir bar (not shown). Light can be applied by a fiber optic cable. Inhibitors such as DCMU can be applied by a syringe through the capillary of the lid. The bottom of the chamber is sealed by a thin gas-permeable Teflon membrane supported by a stainless steel frit. Gases dissolved in the cell suspension AZD8931 chemical structure (indicated by white circles) can diffuse through the membrane and enter

the ion source of the MS by a vacuum line. The addition of heavy isotopes can be applied to differentiate between respiration (uptake of 18O2) and oxygenic photosynthesis (production of 16O2), as well as between CO2 assimilation (uptake of 13CO2) and respiratory CO2 production (12CO2). The metabolism of D2 is an indicator of the hydrogen metabolism and the hydrogenase turnover rate. b Schematic graph of the effect of DCMU on the in vivo H2 -production rate of S-depleted C. reinhardtii cells as recorded utilizing the MS system depicted in (a). A stable H2 graph indicates the instantaneous H2 evolution rate PI-1840 of an illuminated, S-deprived algal culture. To define the contribution of photosynthetic water splitting to the electron supply of the hydrogenase, DCMU is

added. The difference of the H2-production rates before and after the addition of the PSII inhibitor is equivalent to the fraction of H2 which is generated with electrons provided by PSII. To determine the low rate of dark H2 production, light is turned off after the H2 graph has stabilized. The merit of this set-up is that changes of the concentrations of several gases can be recorded simultaneously. The spectrometer sequentially scans the abundance of the gases of interest while measuring one mass peak takes 0.5 s in the system described by Lindberg et al. (2004). Therefore, the concentrations of gases dissolved in a cell suspension within the measuring chamber are recorded in very short-time intervals and any change in gas abundance will be observable almost immediately. Thus, this MS system allows examining different metabolic processes in real time and in parallel, allowing a direct comparison without the need to take into account different measuring conditions and set-ups (e.g., light intensity, temperature, disturbance of the system by entry of air etc.).