Role of illumination intensity in microcystin development using Microcystis aeruginosa as the model algae

Abstract

Microcystis aeruginosa (M. aeruginosa) is one of the most common genera of cyanobacteria in algal blooms. In the present work, the impact of the illumination intensity on the growth of M. aeruginosa has been studied and a grinding method for the extraction of intracellular microcystins (MCs) was developed. The variations of algal density, pH, total phosphorus (TP), and total nitrogen (TN) have been investigated during MCs' culturing period. Results showed that the extraction efficiency of MC-YR by the grinding method was 275% higher than the sonication method, and the extraction efficiencies of MC-RR and MC-LR by the grinding method were similar to the sonication method. The optimal illumination intensity for M. aeruginosa was found to be 19-38 μmol m s with suitable pH range of 7.5-10.5. Active release of extracellular MCs was not significantly observed when illumination intensities were ≤ 38 μmol m s. Furthermore, the intracellular MC yields under different illumination intensities were found to be a relatively stable level. However, excess illumination intensity (≥ 47 μmol m s) led to the lysis of algal cell and increased the concentrations of extracellular MCs, with MC-RR as the dominant compound. The calculated intracellular/extracellular MCs ratios for MC-RR, MC-LR, and MC-YR were 2.38 (N = 100, SD = 2.44), 2.68 (N = 64, SD = 3.48), and 1.25 (N = 30, SD = 1.64), respectively. Strong illumination intensity and cell lysis were found to be the two major factors influencing the release of extracellular MCs.

The proliferation rule of Microcystis aeruginosa under different initial pH conditions and its influence on the pH value of the environment

“…This study found that during the growth of M. aeruginosa, the pH value of the algal culture increased rapidly with a slight increase in algal density before reaching the maximum value (Fig. 3b), which was also observed by Liu et al (2017). Before reaching the highest pH value, the pH value of Synechococcus increased rapidly to approximately 9.6 with a slight increase in biomass (Bundeleva et al 2014).…”

“…3a), which may be due to the buffering capacity of algae in response to the pH value of water. When the environmental pH is not conducive to the growth of algae, its self-adaptability enables it to adjust the pH value of the water to be suitable for its growth through a series of physiological and biochemical reactions (Liu et al 2017;Wei et al 2020). However, in this study, M. aeruginosa was unable to exchange substances freely with the outside world in a quite narrow and enclosed environment, and the self-regulation and buffer capacity of the culture environment were relatively weak.…”

The Proliferation Rule of Microcystis Aeruginosa Under Different Initial pH Conditions and its Influence on the pH Value of the Environment

“…The increase in water pH reduces the content of CO 2 , which is easily absorbed by algae, and HCO This study found that during the growth of M. aeruginosa, the pH value of the algal culture increased rapidly with a slight increase in algal density before reaching the maximum value (Fig. 3b), which was also observed by Liu et al (2017). Before reaching the highest pH value, the pH value of Synechococcus increased rapidly to approximately 9.6 with a slight increase in biomass (Bundeleva et al 2014).…”

“…These ndings proved the credibility of the previous speculation that pH uctuations are associated with photosynthesis and inorganic carbons. However, the mechanism of the short-term uctuation still needs further study; that is, the pH values of algal cultures always rise and fall irregularly over 24 h. (2017) found that the density of M. aeruginosa was higher when the environmental pH value was 9.2-10.5, Liu et al (2017) determined that the optimal growth pH range of M. aeruginosa was 7.5 to 10.5, and Chandra and Rajashekhar (2016) found that M. aeruginosa could grow at high alkaline pH (9.0-10.0). These results are consistent with our experimental results; that is, the optimal pH value for the proliferation of M. aeruginosa was 9.56 (Fig.…”

Algicidal characterization and mechanism of Bacillus licheniformis Sp34 against Microcystis aeruginosa in Dianchi Lake

“…Illumination has a significant impact on the growth of microalgae . To find whether illumination would also affect the algicidal ability of the Sp34 supernatant against M. aeruginosa DCM4, the algicidal ratio under full light (24‐h light), light and dark cycle (14:10 h) and dark (0‐h light) conditions were examined.…”