Circadian rhythm promotes the biomass and amylose hyperaccumulation by mixotrophic cultivation of marine microalga Platymonas helgolandica

Abstract

Background Microalgal starch can be exploited for bioenergy, food, and bioplastics. Production of starch by green algae has been concerned for many years. Currently commonly used methods such as nutrient stress will affect cell growth, thereby inhibiting the production efficiency and quality of starch production. Simpler and more efficient control strategies need to be developed. Result We proposed a novel regulation method to promote the growth and starch accumulation by a newly isolated Chlorophyta Platymonas helgolandica. By adding exogenous glucose and controlling the appropriate circadian light and dark time, the highest dry weight accumulation 6.53 g L−1 (Light:Dark = 12:12) can be achieved, and the highest starch concentration could reach 3.88 g L−1 (Light:Dark = 6:18). The highest production rate was 0.40 g L−1 d−1 after 9 days of production. And this method helps to improve the ability to produce amylose, with the highest accumulation of 39.79% DW amylose. We also discussed the possible mechanism of this phenomenon through revealing changes in the mRNA levels of key genes. Conclusion This study provides a new idea to regulate the production of amylose by green algae. For the first time, it is proposed to combine organic carbon source addition and circadian rhythm regulation to increase the starch production from marine green alga. A new starch-producing microalga has been isolated that can efficiently utilize organic matter and grow with or without photosynthesis.

Transcriptomics reveal how circadian regulation contributes to starch hyperaccumulation in marine alga Tetraselmis helgolandica

“…Under 10 g/L glucose (Glc) and L:D (L:D) = 6:18 (h), T. helgolandica could accumulate the highest starch density (3.88 g/L) and the highest proportion of amylose (Am/Ap = 1.87; Figure 1B). In previous studies, we also detected changes in cellular physiological parameters and the ratio of amylose/amylopectin at different time points (Shi et al., 2022). The intracellular starch content of T. helgolandica was then monitored with time for 1 day (Figure 1C), and the trend of starch content was similar between the two groups under continuous light (L:D = 24:0 h, ±Glc).…”

“…China, streaking on the plate repeatedly to purify to sterility in the laboratory. The culture conditions was described in our previous study (Shi et al., 2022).…”

“…(1988). The dry weight was measured by the same way described in our previous study (Shi et al., 2022). The changes of starch during 1 day to night were carried out in a total of four groups of ±glucose and ±circadian.…”

“…The starch concentration and amylose/amylopectin ratio (Am/Ap) was measured by the methods described by Hovenkamp-Hermelink et al (1988). The dry weight was measured by the same way described in our previous study (Shi et al, 2022). The changes of starch during 1 day to night were carried out in a total of four groups of ±glucose and ±circadian.…”

“…T. helgolandica is a unique species of Chlorophyta that grows in the coastal waters of China. In our previous study, we have revealed a special phenomenon that carbon addition and regulating circadian rhythm could promote starch synthesis, especially amylose, in T. helgolandica (Shi et al., 2022). The special starch structure has aroused our interest.…”