Study Relationship Between The Quorum Sensing System, PHB Accumulation And The Photopruduction Of Hydrogen In Rhodobacter Sphaeroides

It has long been assumed that bacteria are free-living, unicellular organisms until the phenomenon of bacterial quorum-sensing. Quorum sensing (QS) is a physiological behavior, that the bacteria produce a self-inducing material (Autoinducer, AI) as signal molecules for sensing cell density to regulate gene expression. Quorum intended as "quorum" in English and here it is skilfully used to as a certain degree of bacterial density.Different quorum-sensing system respond to different signal molecules to regulate gene expression, indicating that the behavior of multi-cellular organisms. Most signal molecules are N-acylhomoserine lactone derivatives AI-1 in Gram-negative bacteria; the signal molecules are usually oligo-peptide in Gram-positive bacteria; there is a class of signal molecules which is a new acyl acid 2-furan resin AI-2 which have been regarded as a "universal" signal molecule.Rhodobacter sphaeroides is a Gram-negative bacteria, one of the most important member of photosynthetic bacteria, and also it will produce hydrogen in the light of heterotrophic anaerobic conditions. It can generate 7,8-cis-N-(tetradecenoyl) homoserine lactone, which was named cer quorum sensing system. Research the QS system of Rhodobacter sphaeroides influence on the hydrogen production behavior not only conducive to the overall interpretation of bacterial regulatory networks, but also conducive to the understanding Rhodobacter sphaeroides energy using patterns and regulation. It is also an important guiding significance to future production of biomass. Study the effect of different types of external conditions on the growth of Rhodobacter sphaeroides, preliminary identification of the bacterial optimize conditions for hydrogen production, and through PHB staining to observe bacterial PHB. It was observed that the best growth results of Rhodobacter sphaeroides was under the mode of pH 7.0-8.0, the light intensity for the 2000 lx, temperature for 30℃～35℃and anaerobic-illumination is the best growth mode.5000～9000 lx light intensity,30℃～35℃are more appropriate for hydrogen production. Sodium succinate, sodium pyruvate and glucose are good carbon sources and hydrogen donor in Rhodobacter sphaeroides growth and the hydrogen production.Mastering a simple and economical method to detect PHB content and PHB synthase activity. The best reaction system for detection of PHB synthase activity in vitro are:temperature between 30-45℃; salt concentration of 25%(w/v) NaCl,0.2%(w/v) KC1,0.5%(w/v) MgSO4·7H2O; optimal pH value should be 7.0. Extraction of PHB granules in various growth stages of Rhodobacter sphaeroides, and then adding substrate (Hydroxybutanoyl-CoA), ion concentration and DTNB. Under optimum conditions of temperature and pH, read the reaction absorbance value (A) at 412 nm, through the thiol (-SH) standard curve to calculate the concentration of PHB synthase activity.The signal molecules were detected successfully used colorimetry and biosensor. It founded that the concentration of signal molecules has a good linear relationship with the absorbance at 520nm used the colorimetey method. But because there is no standard signal molecules of Rhodobacter sphaeroides, this method can only detect the existence and relative concentration of signal molecules.The signal molecules of Rhodobacter sphaeroides can promote the bacteria scattered growth in logarithmic phase. There is little effect to the end of stable bacteria. The bacterial growth was inhibited by adding the supernatant of category. Treated the bacteria with signal molecules can significantly change the carbon metabolism and presumably the result is bacteria priority to use signal molecules as energy source.Study the relationship between quorum sensing and hydrogen production in Rhodobacter sphaeroides in hydrogen-producing reactor. Adding different concentrations of signal molecules as inducers, by detection of PHB contents, PHB synthase activity and hydrogen production volume, comprehensive analysis of the relationship between the quorum sensing and hydrogen production. The results showed that signal molecules in hydrogen production can inhibit the activity of PHB synthase during logarithmic phase and thus inhibit the formation of PHB, making it has more reducing power for the production of hydrogen. Quorum sensing can regulate the activity of enoyl-(acyl carrier protein) reductase and then regulate the PHB synthase activity; during end stage in bacteria, signal molecules can regulate their own metabolism, through using the energy generated from PHB decomposition to maintain the survival of bacteria.