Stress is not limited to humans—microscopic organisms like microalgae also experience stress when their living environment changes. Studies on green microalgae, Chlorella sp., reveal how environmental stress can trigger significant changes in their cell structure and composition.

Microalgae: Single Cells, Big Potential

Chlorella is a genus of unicellular microalgae that has long been studied for its ability to produce various high-value metabolites such as pigments, antioxidants, and lipids. When cultured under different conditions—namely photoautotrophic (light-dependent) and mixotrophic (a combination of light and organic carbon sources like glucose)—these microalgae exhibit notable morphological and biochemical changes.

Response to Stress: From Green to Red

Under stressful conditions, microalgae adapt by activating their defense metabolism. This includes:

• An increase in cell size, resulting from the accumulation of lipids and other energy storage compounds.
• Color changes, from green to yellowish or reddish, due to increased production of pigments such as lutein and astaxanthin.
• Production of secondary metabolites, including antioxidants like carotenoids and phenolic compounds, which protect cells from oxidative damage.

Interestingly, mixotrophic conditions that induce moderate stress were found to increase carotenoid content, while chlorophyll and phenolic compound levels decreased. Nevertheless, the overall antioxidant capacity was maintained through carotenoid activity and other supporting compounds.

Electron microscopic images of Chlorella zofingiensis under (a) normal and (b) stress conditions. (Source: Azaman et al., 2017)

Implications for Industry and Research

Understanding how microalgae respond to stress opens up vast opportunities across multiple application areas:

• Food and health supplement industries: production of natural antioxidants.
• Natural cosmetics: algae based pigment and skin protective agent.
• Biofuels: production of oils and lipids during stress induction condition.

It is important to ensure that culture conditions are carefully controlled so that the desired metabolites can be optimally produced without compromising cell health.

A Mirror of the Human Body: Stress at the Cellular Level

The way microalgae manage stress closely mirrors how human cells respond:

• Hormonal changes that trigger shifts in metabolism (e.g., cortisol and adrenaline).
• Enhanced oxidative defenses to neutralize harmful free radicals.
• Increased fat storage, especially during prolonged stress—just like microalgae that accumulate lipids.

This phenomenon—known as hormesis—shows that a small amount of stress can strengthen biological systems. However, when stress is excessive or prolonged, it leads to damage: pigment loss and cell deterioration in algae, and inflammation and disease in humans.

Why It Matters? : From Algal Cultures to Everyday Life

Understanding stress in microalgae is not just an academic exercise—it has real-world relevance. By studying their resilience, scientists are optimizing the production of beneficial compounds for supplements and cosmetics.

At the same time, this research offers us a powerful metaphor: stress, when wisely managed, can lead to transformation. Whether through exercise, fasting, or mental challenges, small doses of stress can spark positive changes in our bodies as well.

Conclusion

Microalgae may be tiny, but their survival strategies carry a profound message. When life becomes challenging, these organisms don’t collapse—they adapt. They protect themselves. They become stronger. Just like us. By learning from the wisdom of nature, we can learn how to thrive under pressure—and perhaps turn stress into strength.

 

References:

Azaman SNA, Nagao N, Yusoff FM, Tan SW, Yeap SK. 2017. A comparison of the morphological and biochemical characteristics of Chlorella sorokiniana and Chlorella zofingiensis cultured under photoautotrophic and mixotrophic conditions. PeerJ 5:e3473 

Hill, Y., Kiefer, A. W., Oudejans, R. R., Baetzner, A. S., & Den Hartigh, R. J. (2024). Adaptation to stressors: hormesis as a framework for human performance. New Ideas in Psychology, 73, 101073.

Mishra, N., Gupta, E., Singh, P., & Prasad, R. (2021). Application of microalgae metabolites in food and pharmaceutical industry. In Preparation of Phytopharmaceuticals for the Management of Disorders (pp. 391-408). Academic Press.

 

Author:

Dr. Siti Nor Ani Azaman

Biology Unit,

Centre of Foundation Studies In Science Universiti Putra Malaysia (ASPutra).

 

Date of Input: 16/07/2025 | Updated: 16/07/2025 | hasniah