The effects of physical and chemical factors on the growth and lipid production of Chlorella
The effects of nitrogen, phosphorus, iron, salinity, light intensity, and temperature on the growth rate,hiomass, and lipid accumulation of Chlorella sp. XQ-200419 in aerated cultures were investigated. The main results are as follows: Both the growth and lipid accumulation of Chlorella sp. XQ-200419 are significantly affected by the nitrogen concentration in the BG11 medium. Growth rate and biomass increase with increasing KNO3 concentration from 0.05g/L to 0.3g/L, however lipid content decreases. Maximum lipid production was realized when the KNO3 concentration was 0.3g/L. There were no obvious effects on the growth and lipid accumulation of Chlorella sp. XQ-200419 when the K2HPO4 concentration ranged from 10 mg/L to 160mg/L. The growth rate was not affected by supplementing the growth media with chelated FeCl3 in the late growth phase. whereas, the lipid content did increase with increasing supplemented Fe3+ concentration. Both the lipid content and lipid production were maximized when cultures were supplemented with 0. 75mol/L Fe3+. Growth of Chlorella sp. XQ-200419 was inhibited to some extent by salinity. With NaCl concentrations of 0. 2mol/L or less, the lipid content increases with the increases in salinity. When the NaCl concentration was 0. 6mol/L, the lipid content declined significantly. Lipid content and lipid production both were maximized with a NaCl concentration of 0. 2mol/L. The growth of Chlorella sp. XQ-200419 was only slightly affected by changing the light intensities in the late growth phase. However, lipid accumulation was greatly affected. Lipid content and lipid production significantly increased with the increased light intensity. Maximal lipid content and lipid production were achieved at the highest light intensity used 280μmol m-2s-1. Temperature significantly impacted growth rate, biomass, lipid content, and lipid production. With the increases in temperature from 15℃ to 40℃, the growth rate, biomass, lipid content and lipid production all initially increased and then decreased. The optimal temperature range for growth and lipid accumulation is from 20℃ to 35℃. Lipid production was maximized between 30℃ and 35℃. Cultivation at 40℃ caused minimal biomass, lipid content, and lipid production. There are two patterns by which physical and chemical factors act on the growth and lipid content of Chlorella sp. XQ-200419. When temperature, light intensity, Fe3+ and salinity are applied at an optimal range they have a promoting effect on both growth and the lipid content of the alga, which can be termed as "fit mode". In the second pattern, low nitrogen concentration leads to an increased lipid content but inhibits the growth of the alga. This is termed "stress mode".Both modes increase lipid content, but only the "fit mode" increases lipid production. To select good oil-producing strains of Chlorella, it is also worth noting that only strains that achieve higher oil content under suitable culture conditions have high potential for oil production.
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