# Comparative Analysis of Microalgae’s Physiological Responses to Fibrous and Layered Clay Minerals

## TL;DR

This study compares how two types of clay minerals affect the growth and function of a model green alga, finding that fibrous palygorskite harms algae more than layered montmorillonite.

## Contribution

The study reveals distinct physiological impacts of fibrous versus layered clay minerals on algal cells, offering new insights into natural algal-mineral interactions.

## Key findings

- Palygorskite reduced algal cell counts and inhibited photosynthesis more severely than montmorillonite.
- Palygorskite decreased extracellular proteins, polysaccharides, and phosphorus uptake in algal cells.
- Montmorillonite had minimal effects on algal physiology and did not significantly alter cell surface interactions.

## Abstract

Microalgae are key to aquatic ecosystems, supporting food chains and nutrient cycles. Clay minerals, common in water, can either help or hinder algae—boosting growth by providing nutrients or harming them by blocking light. This study compared two clays, flat-layered montmorillonite and needle-like palygorskite, testing their impact on Chlamydomonas reinhardtii, a model green alga. We measured the algae’s growth, photosynthesis, cell structure, slimy coatings, and genetic responses. The results revealed that montmorillonite may support algae better due to its high surface area, while palygorskite’s sharp fibers could damage cells. These findings help explain how clays naturally influence algae, offering insights for managing harmful blooms or promoting useful algae in clean energy and water treatment.

Microalgae interact with mineral particles in an aqueous environment, yet how clay minerals affect physiological processes in algal cells remains unexplored. In this study, we compared the effects of palygorskite (Pal) and montmorillonite (Mt), which respectively represent fibrous and layered clay minerals, on the physiological processes of Chlamydomonas reinhardtii. It was observed that C. reinhardtii responded differently to the treatments of Pal and Mt. The Pal particles bound tightly to and even inserted themselves into cells, resulting in a significant decrease in cell numbers from 27.35 to 21.02 × 107 mL−1. However, Mt was only loosely attached to the cell surface. The photosynthesis in the algal cells was greatly inhibited by Pal, with the rETRmax significantly reduced from 103.80 to 56.67 μmol electrons m−2s−1 and the downregulation of IF2CP, psbH and OHP1, which are key genes involved in photosynthesis. In addition, Pal reduced the quantities of proteins and polysaccharides in extracellular polymeric substances (EPSs) and the P uptake by C. reinhardtii when the P level in the culture was 3.15 mg/L. However, no significant changes were found regarding the above EPS components or the amount of P in algal cells upon the addition of Mt. Together, the impacts of fibrous Pal on C. reinhardtii was more profound than those of layered Mt.