Achille Pozzi

X-ray irradiation of yeast cells

Saccharomyces Cerevisiae yeast cells were irradiated using the soft X-ray laser-plasma source at Rutherford Laboratory. The aim was to produce a selective damage of enzyme metabolic activity at the wall and membrane level (responsible for fermentation) without interfering with respiration (taking place in mitochondria) and with nuclear and DNA activity. The source was calibrated by PIN diodes and X-ray spectrometers. Teflon stripes were chosen as targets for the UV laser, emitting X-rays at about 0.9 keV, characterized by a very large decay exponent in biological matter. X-ray doses to the different cell compartments were calculated following a Lambert-Bouguet-Beer law. After irradiation, the selective damage to metabolic activity at the membrane level was measured by monitoring CO2 production with pressure silicon detectors. Preliminary results gave evidence of pressure reduction for irradiated samples and non-linear response to doses. Also metabolic oscillations were evidenced in cell suspensions and it was shown that X-ray irradiation changed the oscillation frequency.

An ensemble of new techniques to study soft-X-ray-induced variations in cellular metabolism

An ensemble of new techniques has been developed to study cell metabolism. These include: CO2 production monitoring, cell irradiation with soft X rays produced with a laser-plasma source, and study of oscillations in cell metabolic activity via spectral analysis of experimental records. Soft X-rays at about 0.9 keV, with a very low penetration in biological material, were chosen to produce damages at the metabolic level, without great interference with DNA activity. The use of a laser-plasma source allowed a fast deposition of high doses. Monitoring of CO2 production allowed us to measure cell metabolic response immediately after irradiation in a continuous and non invasive way. Also a simple model was developed to calculate X-ray doses delivered to the different cell compartments following a Lambert-Bouguet–Beer law. Results obtained on Saccharomyces cerevisiae yeast cells in experiments performed at Rutherford Appleton Laboratory are presented.

Microscopy characterization of doped fibers

The use of the Soft X-ray Contact Microscopy technique is discussed as a possible new tool to get information on dopant distribution in the core of single-mode optical fibers with 50 nm spatial resolution.

Differential two-color x-ray radiobiology of membrane/cytoplasm in yeast cells and lymphocytes

An overall approach into the differential investigation of membrane/cytoplasm related metabolism and of cell-cycle of yeast cells after two color soft X-ray irradiation is presented; the soft X-rays being generated in trains of picosecond pulses by laser-plasma interaction. The two color X-ray differential technique is based on the generation of approximately 0.6 KeV X-rays which are deposited only in the membrane-wall complex switching off the anaerobic (fermentative) activity of yeast cells and on the generation of approximately 1.2 KeV X-rays which are mainly deposited in the cytoplasm, mitochondria and nucleus of yeast cells, mainly affecting the aerobic metabolism. A synergetic analysis of the metabolism is discussed, mainly founded on the recording of different correlated metabolic parameters, both on-line and delayed. Among the relevant access, pressure monitoring in batch samples acquire a dominant role allowing the identification of metabolic oscillation, that represent a marker of physical and chemical actions performed on the samples at different times. The experience acquired on yeast cells metabolism is being used to investigate lymphocytes metabolism and the related oscillatory properties of relevant enzymatic complexes. Actually even if it is not exactly the same as the mammalian situation, it should really propel the whole field forward.

Soft x-ray-controlled dose deposition in yeast cells: techniques, model, and biological assessment

A procedure is presented to release soft x-rays onto yeast cell membrane allegedly damaging the resident enzymatic processes connected with fermentation. The damage is expected to be restricted to regulating fermentation processes without interference with respiration. By this technique fermentation is followed leading to CO2 production, and respiration resulting in global pressure measurements. A solid state pressure sensor system has been developed linked to a data acquisition system. Yeast cells cultures have been investigated at different concentrations and with different nutrients. A non-monotone response in CO2 production as a function of the delivered x-ray dose is observed.

Allosteric enzyme behavior: the onset of oscillations EM field sustained

The experimental set up is discussed for yeast fermentation monitoring in connection with irradiation procedures. The key role of the PFK enzyme is examined and a model for ATP-ADP competition is presented.