Study Function Of Quorum Sensing In Hydrogen-producing Rhodobacter Sphaeroides

Bacteria can produce signal molecule known as "autoinducer" to apperceive self number and the number of other bacteria, with the increase of bacterial density, signal molecule concentration increases, when it reaches a certain threshold, the whole bacterial communities will make adjustments of gene expression, so that bacteria can adapt to the environment, the system known as quorum sensing.Gene regulation of bacteria by quorum sensing is a very universal phenomenon, for example, quorum sensing can induce cell into the stationary phase, mediating mobile of bacterial groups, and so on, with the capacity of a variety of physiological regulation. Quorum sensing closely linked with cell density, and the change of cell density and nutrients is directly related, so nutrition starvation and quorum sensing are necessarily related, evenmore, signal molecules of quorum sensing is necessary for the growth of microorganisms.Rhodobacter sphaeroides is a free-living, one of the most important member of photosynthetic bacteria, and also is a photosynthetic bacteria with hydrogen-producing capacity, it will produce hydrogen in the light of heterotrophic anaerobic conditions. It is Gram-negative bacteria, founding it can generate 7,8-cis-N-(tetradecenoyl) homoserine lactone, which was named cer quorum sensing system. Studying impact of autoinducer on cell growth, starvation-survival and resuscitation of R. sphaeroides, father to study regulation of energy use by quorum sensing, it has guiding significance on physiological behavior of hydrogen-producing.Near-natural pure culture technique is based on the quorum sensing, it can simple simulation the information transmission mechanismn between bacteria, so that it make physiological behaviour of bacteria differ from the traditional culture. In the experiments, using hole plate, bacteria can comunication through membrane-mediated signal transduction. The results showed that the near-natural pure culture technique is differ from traditional culture on colony phenotype. If adding exogenous signal molecule as inducer whose structure is similar to that of the bacteria in the plate, founding the bacteria has moving and gathering physiological behavior. Under near-natural pure liquid culture, stuying impact of autoinducer on cell growth, the result showed that adding the supernatant of the same genus bacteria as liquid medium, growth of bacteria has been inhibited. While adding signal molecule in the medium, founding the growth of bacteria was also inhibited, and the high concentration of signal molecules has inhibited great of the growth.In order to study impact of signal molecules on starvation-survival and resuscitation in the experiments, adding signal molecules at different culture conditions, by measuring the total bacterial counts and viable bacterial counts to study the quorum sensing impact on bacteria quanlity. The results showed: the quorum sensing existing in R. sphaeroides can make different modulation of bacteria at different growth stages when confronted with starvation environment. QS has greater ability to control the log-bacteria, and has maintained higher viable counts, and signal molecules can make bacteria to better use of EDTA to maintain viable bacterial counts under half-starvation; After the bacteria were put under the pressure of high-density growth and in a nonculturable state, it can be observed that adding signal molecules will help their quick recovery, whereas after different starvation condition of two weeks, the existence of signal molecules can maintain high number of viable bacteria during resuscitation, and also found that avoid oxygen toxicity can maintain better cell activity.In order to study the regulatory function of cer quorum-sensing system on the carbon utilization in R. sphaeroides. The research was done by adding exogenous signal molecule as inducer, and using Biolog-GN identification plate to study the utilization of ninty five single carbon source under normal culture and after starvation. The results showed: R. sphaeroides can use exogenous signal molecule, and activating metabolic regulation of carbon source in six hours.While after starvaton, bacteria transfered to the plate with signal molecule can use more types of carbon source to resume cell viability, and the normal cultured bacteria has higher degree use of carbon source; The regulation of signal molecules on carbon source relating to the common energy ATP, NAD(P)H and variety enzyme involved in metabolic pathways. In the study of bacterial hydrogen production, exploration of the different external conditions for the production of hydrogen, such as bacterial activity, temperature, light intensity, pH. Hydrogen-producing is appropriate physical behaviorin when bacteria facing feasible environment, and quorum-sensing is gloable regulation of intracellular cell, in order to explain the relationship between hydrogen production and quorum-sensing, adding different concentration of signal molecules to reactor, by measuring hydrogen production capacity and the number of viability bacteria to approve the impact of signal molecules on hydrogen production.The results showed: the log-phase bacteria transfered to the medium has larger amount of hydrogen production; optimization pH of hydrogen production in the range 7.0 to 8.0, alkaline environment is obviously not conducive to relasing hydrogen; light intensity between 50001x ~ 70001x is suit for hydrogen production; the suitable temperature of hydrogen production is range 30 to 35℃; signal molecules has impact on hydrogen production, different concentrations of signal molecules has different influence. Adding signal molecules at the final concentration of 10μM, bacteria is tend to the way to hydrogen production, with higher hydrogen production, at the same time found that at high hydrogen production, the viable bacteria is little.