The importance of surface morphology cannot be overstated, because it not only determines the fate of microorganisms, but also significantly affects their physiological status. For instance, microalgae Scenedesmus abundans have been observed to display discernible surface epistructures in the exponential phase. In addition, when microorganisms age, their surface morphology undergoes an intriguing transformation from ruffled to smooth. By closely examining the surface morphology of microorganisms, we can gain a better understanding of their unique characteristics and how they adapt to their environment over time. However, although qualitative scanning electron microscopy (SEM) images can provide useful visual information, they are not as reliable as quantitative analysis in terms of providing accurate measurements and detailed insights into physiological changes. We then constructed the electrorotation system to rotate microorganisms and quantitatively observe the changes in surface morphology during the aging process of microalgae.

The cover image of the May 16 issue of Biophysical Journal is an SEM image of microalgae in the stationary phase. During our examination of cell surfaces, we observed the presence of degenerated spines and fins, as well as a smooth surface with multiple warts on microalgae in the stationary phase. The observed changes in microalgae surface morphology led to a uniform rotational speed when they were rotated. On the other hand, two groups of rotational speeds were observed in microalgae during the exponential phase, which exhibited various epistructures, such as fin-like ridges, hook-like spines, or underdeveloped ones. This suggests that the presence of these external structures affects the rotational behavior of microorganisms and provides insight into the relationship between surface morphology and physiological properties. As previously mentioned, our goal was to quantify the impact of surface morphology on the behavior of microalgae. To accomplish this, we introduced a new parameter into the electrorotation model called the "surface factor." This value allows us to accurately express the dynamic changes in microalgal surface morphology throughout their lifespan, providing valuable insights into how these changes affect the rotational behavior of the microorganisms. By measuring and analyzing the surface factor, we can better understand the complex biology and behavior of microalgae and how they adapt and evolve over time.

By means of our investigation and this cover, we emphasize the potency of merging experimental and theoretical methodologies in confronting intricate challenges, particularly in relation to fundamental issues at the interface of biology, chemistry, and physics.

— Yu-Sheng Lin, Chen-li Sun, Sung Tsang, Sakina Bensalem, Bruno Le Pioufle, and Hsiang-Yu Wang