| Chlorella pyrenoidosa is a kind of unicellular freshwater algae with high nutritional value and excellent application prospects,which is rich in proteins,lipids,pigments,vitamins,etc.When the light and external organic carbon sources exist at the same time,C.pyrenoidosa can utilize both organic carbon and inorganic carbon under mixotrophic culture.In this culture mode,the photosynthesis and the metabolism of external organic carbon run simultaneously.Therefore,the growth and metabolism of cells are affected by the supply of light and organic carbon sources.However,numerous studies have shown that the mixotrophy is not the simple combination of autotrophy and heterotrophy.Currently,the regulation of light and glucose(a kind of common organic carbon source)supply on cell growth and component accumulation is still not clear in the mixotrophic culture of C.pyrenoidosa.To solve this problem,this paper comprehensively investigated the effects of glucose concentration and light intensity on the culture of C.pyrenoidosa and systematically analyzed the cell growth,substrate consumption and component accumulation of C.pyrenoidosa.At last,the effect of light on photosynthesis and glucose metabolism pathways was explored.The main results were as follows:(1)Cell density:The effect of initial glucose concentration on cell division was not significant.However,a low light intensity promoted the increasing of cell division under mixotrophic growth.The cell division of C.pyrenoidosa was significantly inhibited by the increasing of light intensity.As a result,the specific growth rate of cell division was about 0.44?0.45 day-1 at a low light intensity of 15 pmol/m2/s when the glucose concentration was 5 and 10 g/L.But the specific growth rate decreased to 0.38?0.41 day-1 when the light intensity increased to 30 and 90 ?mol/m2/s.(2)Cell size:The increasing of cell size was promoted by the increasing the glucose concentration within a certain light intensity range,while the cell size was inhibited by the increasing the glucose concentration under a high light intensity.The final cell size increased from 3.35?4.37 ?m to 4.74-5.39 ?m under the light within of 0-30 ?mol/m2/s when the glucose concentration was increased from 2 g/L to 10 g/L.However,the final cell size decreased from 5.43 ?m to 5.13 ?m when the high light intensity increased at 90?mol/m2/s.On the other hand,the increasing of cell size could also be promoted by the increasing of light intensity.However,the cell size was inhibited by a high light intensity at high glucose concentrations.(3)Biomass accumulation:The final biomass and biomass productivity of C.pyrenoidosa were improved by the increasing of either glucose concentration or light intensity under low light intensity or initial glucose concentration,respectively.Whereas,a high light intensity significantly inhibited the biomass accumulation of C.pyrenoidosa at a high initial glucose concentration.The final biomass concentration and productivity were the highest at a glucose concentration of 5 g/L and a light intensity of 30 ?mol/m2/s,which reached 3.99±0.04 g/L and 0.54±0.01 g/L/day,respectively.Howver,the final biomass concentration and productivity significantly decreased to 3.21±0.09 g/L and 0.43±0.01 g/L/day when the glucose concentration and light intensity increased to 10 g/L and 90?mol/m2/s at the same time.(4)Glucose utilization:The utilization rate and efficiency of glucose were not significantly affected by the initial glucose concentration.However,the utilization of glucose was significantly inhibited by the increasing the light intensity.The cell utilization rate and efficiency of glucose was 57.58%and 1,35 g/L/day respectively decreased to 25.14%and 0.36 g/L/day as the light intensity increased from 15?mol/m2/s to 90?mol/m2/s at the initial glucose concentration of 10 g/L.(5)Component accumulation:The final lipid content of C.pyrenoidosa was significantly increased,while the final protein content was significantly decreased with the increasing of glucose concentration and light intensity.The highest final lipid content of 36.13%and the lowest protein content of 46.08%were achievedunder the light intensity of 90 ?mol/m2/s and the glucose concentration of 10 g/L.In addition,the starch accumulation was promoted by increasing the glucose concentration.However,a high light intensity inhibited the accumulation of starch.Therefore,the highest starch content of 27.00%was reached under the heterotrophic culture with a glucose concentration of 10 g/L.Above results showed that light had significant effects on cell growth and glucose metabolism in mixotrophic culture.However,when photosynthesis pathway was inhibited,cell growth and glucose metabolism in mixotrophic culture were similar to those in heterotrophic culture.Transcriptome analysis showed that photosynthesis,glycolysis pathway and TCA cycle were enhanced,while pentose phosphate pathway was weakened.The enhancement of photosynthesis promoted photosynthetic carbon fixation and biomass accumulation.However,it inhibited the utilization of glucose and thus,the biomass accumulated through glucose was reduced.This paper comprehensively analyzed the regulation of light and glucose supply on the cell growth and component accumulation of C.pyrenoidosa,which had great significance for improving biomass production and energy utilization efficiency.Moreover,this paper provided relevant information in the actual production of C.pyrenoidosa. |
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