The effect of light intensity and carbon flux on the production of chlorophyll a and B-phycoerythrin, as well as their ratios in the batch culture of Porphyridium purpureum, has been studied. It is shown that with an increase in light intensity (by 2 times) and air supply speed (by 2 times), the value of maximum productivity increases by almost 2 times, the concentration of chl a – by 1.8 times, and B-PE – by 1.6 times. The content of chlorophyll a and B-phycoerythrin in all experimental variants on the 3rd – 4th day of the experiment (the beginning of the linear growth phase) reached the maximum value. With light limiting, the content of chl a and B-PE in the biomass does not change, however, with high light intensity, a decrease is observed in the linear growth phase. The ratio of B-PE/chl a with different light and carbon support in the experiment practically does not change and averages 12.8.
The work focuses on the modeling the light-dependent growth of Arthrospira platensis. During the experimental study, we obtained a batch curve, which characterizes the presence of a long linear phase. We showed that the constant culture productivity is determined by the light conditions in which cells are located. The simplest model of the light-dependent growth of a batch culture is proposed. The model is based on the assumption that the specific growth rate is determined by the surface irradiation, the light absorption coefficient, and the concentration of chlorophyll a. Verification of the obtained equations indicates that the constant productivity is observed only in the case of a hyperbolic decrease chlorophyll a content and other structural compounds of microalgal biomass. A method for rapid assessment of the concentration of photosynthetic pigments in the A. platensis culture by its absorption spectrum using the sum of Gaussian curves is proposed. Mathematical decomposition of the absorption spectrum of A. platensis was carried out, all Gaussian parameters were calculated. For the red part of the spectrum, a simple expression is presented that allows one to estimate the concentration of chlorophyll a and phycobiliproteins. The native extinction coefficient of chlorophyll a at 678 nm was calculated to be 65 l·g-1·cm-1. We proposed an algorithm for determining the concentration of photosynthetic pigments directly from the true absorption spectrum of the A. platensis culture without interfering with its growth processes.
The paper describes a method for mathematical separation of the absorption spectrum of the culture of the red seaweed Porphyridium purpureum using a spreadsheet processor - the Microsoft Excel program. This method represents the analysis and separation of overlapping pigment bands in the native absorption spectrum of a culture. The culture spectra were recorded on a spectrophotometer near and at a distance from the entrance window of the integrating sphere. The true absorption spectrum is calculated, compensated for scattering in the region from 400 to 750 nm. The true absorption spectrum of the culture was approximated by a mathematical model in which the unknown parameters are the concentrations of chlorophyll a, B-phycoerythrin, R-phycocyanin, allophycocyanin, and total carotenoids. Pigment models are represented by the sum of normal distribution curves. The implementation of calculations that perform the selection of pigment concentrations by minimizing the sum of squared deviations between the true absorption spectrum and its mathematical model was performed using a spreadsheet using the "Search for a solution" tool. The proposed method of mathematical processing of the spectrum can be used as an express method for determining the concentration of pigments in culture, without isolating pure pigments. The application of this method makes it possible to evaluate the contribution of pigments to the total absorption spectrum of the culture.
The dynamics of the integral coefficient of light absorption and photobiosynthesis efficiency of dense cultures of microalgae is researched. A batch cyanoprokaryotic culture of Arthrospira (Spirulina) platensis (Nordst.) Gomont was grown under light-limiting conditions. The choice of the light-limiting region is due to the low rates of photobiosynthesis, which, from a methodological point of view, simplifies the determination of the dynamics of biomass concentration and its main biochemical components. An express method for determining the concentration of chlorophyll a from true absorption spectra compensated for scattering is proposed. The production characteristics of culture were calculated (maximum specific growth rate – 0.02 h-1, productivity 0.17 g·l-1·d-1, percentage of Chl a – 1.5%). It is shown their relationship with the surface irradiation of the. It is revealed the dependence of the integral light absorption coefficient on the surface concentration of Chl a is described with high accuracy (R2 = 0.99) by the Bouguer-Lambert-Beer law. The specific absorption rate was 0.02 m2·mg-1, which is 2 times higher than that calculated for green algae. The efficiency of light energy utilization decreased at the exponential growth phase and stabilized at the linear one at the level of 4.9%. The obtained results can be used to predict the production of biologically valuable components in laboratory and semi-industrial conditions.
Mathematical decomposition of the absorption spectrum of the culture of the red microalga Porphyridium purpureum (Bory) Ross was carried out in the spectral range from 550 to 750 nm. The culture spectra were recorded on a spectrophotometer with an integrating sphere. Using the literature data, mathematical models of the absorption spectra of the following pigments were compiled: B-phycoerythrin, R-phycocyanin, allophycocyanin and chlorophyll a. The mathematical model of each pigment represented the sum of Gaussian curves. The resulting equations were taken as a basis for modeling the native spectrum. A general model of the absorption spectrum of culture in the region of 550–750 nm has been compiled, consisting of the sum of individual pigments. Using the model obtained in practice, it is possible to determine the concentrations of chlorophyll a, and individual phycobilin pigments directly from the absorption spectrum of the culture.
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