Elucidating the adaptive response and enhanced lipid production of Chlorella minutissima under Cr (VI) stress

Abstract

The exponential surge in industrialization and urbanization witnessed in recent decades has alarmingly escalated the levels of hazardous pollutants, instigating profound apprehensions regarding environmental safety. In particular, the bioamplification of heavy metals like hexavalent chromium [Cr (VI)] being a prominent example, has not only imposed severe repercussions on human health but has also wrought havoc within the intricate balance of the ecological framework. Rectifying Cr (VI) via bioremediation agents exemplified as microalgae, emerges as an environmentally harmonious strategy. The present study delves into the intricate mechanisms underpinning the adaptive responses of a freshwater microalga, Chlorella minutissima, in the face of Cr (VI) stress. Evidencing exceptional tolerance to Cr (VI) induced stress, this microalga manifested an IC50 value of ~10 ppm while evidencing an astounding removal efficiency of ~89 %. This heightened assimilation of Cr (VI) by the microalgal cells concomitantly accompanied ~1.6 fold rise in total lipid content. The fostered levels of stress metabolites and antioxidant enzymes indicate the activation of defense mechanism to mitigate Cr (VI) induced oxidative damage. Microalgae employ reduction mechanism converting toxic Cr (VI) into the less deleterious Cr (III) where Cr2O3 and CrO (OH) were found to be the prominent species; while Cr (VI) primarily existed as CrO42−. The present study provided a detailed understanding of C. minutissima towards stress tolerance and enhanced lipid production mechanisms incited by chromium exposure.