| Natural astaxanthin is the strongest antioxidant ever found existed in nature by far,and has wide application in many new fields. Haematococcus pluvialis is considered themost promising microorganism producer for natural astaxanthin, yet withcomplex cellcycles, slow growth and low resistance to harmful organisms infection. Cultivatedmixotrophically in light with sodium acetate (NaAc) can maximize improving the growthrates of H. pluvialis, and is one of the most promising ways to realize large-scale culture.However, there are still many problems to be solved.In this thesis, the general and different characteristics of cell growth, photosyntheticperformance index (PIABS) of four strains of H. pluvialis (H0, H2, H3, H6) undermixotrophic (light+NaAc) conditions were studied via combing chlorophyll afluorescence technique. The function procedure and relative mechanism in promoting thegrowth of H. pluvialis with NaAc in mixotrophic mode was preliminary studied. Thencharacteristics of photosynthetic electron transport in H. pluvialis cells during cultivationprocess was in-depth analysed. Furthermore, energy flow and the influence mechanismof NaAc in photosystem II (PSII) of H. pluvialis was explored. In order to make out thebest cultivation schemes, the growth characteristics under different trophic modes werecompared and summarized with strain H2. Besides, the relationships and effectsofnutrient components in medium and different initial inoculation densities to the specificgrowth rate and cultivation cycle of H. pluvialis were investigated with strain H0.Results showed that, all the four strains of H. pluvialis grew well with0.5-2.0g/LNaAc concentrations under mixotrophic condition. Cell densities and the specific growthrate in mixotrophic mode were significantly improved compared to the photoautotrophic and heterotrophic growth modes (investigated with H2). However, the adaptabilities toNaAc and the optimum concentrations for mixotrophic growth varied greatly withindifferent H. pluvialis strains. Strain H0required a relative high NaAc concentration, andcell densities reached63.4×104mL-1on the8th day with2.0g/L NaAc addition. Whilestrain H6sustained comparative short logarithmic growth period and the highest celldensities of H6were only33.0×104mL-1.During the mixotrophic cultivation process, NaAc not only provided organic carbonsubstance to H. pluvialis for heterotrophic growth, but also changed the photosyntheticperformance index (PIABS). The improvement of growth promoted with NaAc additionwas divided into two stages: the fast growth of H. pluvialis during the early culture stageof mixotrophic cultivation was mainly come from its heterotrophic growth, and that at thelate culture stage was mainly contributed by its autotrophic growth. By contrast PSIIenergy absorption efficiency (φPo/(1-φPo)) and other related parameters trends with thechanges of PIABS, as well as combining with regression analysis, we found out that theinfluences of NaAc to physiological status of H. pluvialis under mixotrophic growth weremainly via altering PSII electron transfer efficiency (ψo/(1-ψo)) on the electronic receptorside. The running efficiency of PSII reaction centers (RC/ABS) in four strains of H.pluvialis had no significant changes (P>0.05) with different NaAc addition undermixotrophic growth.The optimum initial inoculation density of H. pluvialis (H0) was not consistentunder different NaAc concentrations. In addition, via combination the cultivation effectwith different carbon nitrogen ratio and comparative analysis under different nutrientcomponents, we discovered that the suitable initial inoculation densities and appropriatenutrient concentrations were closely associated with H. pluvialis cell cycles and itscultivation modes, and the optimal concentrations and the suitable growth conditionsvaried in different strains. Therefore, during the mass cultivation process, in order toobtain the best cultivation effects with mixotrophic culture, NaAc and nutrientconcentrations should varied according to the different growth characteristics of the specific H. pluvialis strain. Meanwhile, the optimal initial inoculation densities shouldalso changed depending on the H. pluvialis growth state (cell cycles).In addition, cell sizes of H. pluvialis varied greatly with comparative high NaAcconcentrations under mixotrophic growth. Therefore, the statistical method via regressionequation was not suitable for H. pluvialis when cultivated in mixotrophic mode withNaAc addition. In our research, we found out that combining chlorophyll a fluorescenceanalysis technique could well track the growth of H. pluvialis in mixotrophic cultivationwith simple work. Photosynthetic performance index (PIABS) could well illustrate thephysiological status of H. pluvialis cultivatied in different NaAc concentrations. Whilecombining chlorophyll fluorescence parameters Fv/Fm(maximum quantum yield forprimary photochemistry at t=0), relative variable fluorescence at J-step VJ, quantum yieldfor electron transport φEoetc. could well grasp the efficiency of PSII energy utilization inH. pluvialis under different experimental treatments. |
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