According to research published this week in The ISME Journal, unicellular diatoms are able to adapt their behavior to different external stimuli. In the study, diatoms directed their orientation towards either nutrient sources or mating partners, depending on their needs.
"It is striking that even unicellular organisms that obviously lack a nervous system can process different stimuli and even evaluate their individual needs,” says senior author Georg Pohnert of Friedrich Schiller University. “Our study showed that diatoms can adapt their behavior flexibly to environmental changes. They also responded differently depending on their need to sexually mate. We observed that the diatoms moved towards pheromones or food sources depending on how hungry they were for sex or nutrients. Until now, this kind of decision-making has only been attributed to higher organisms.”
Diatoms are unicellular microalgae. They dominate marine phytoplankton, which is ubiquitous in our oceans. On shores and beaches, these algae can be observed as biofilms on rocks and other surfaces.
Scientists cultivated Seminavis robusta diatoms with different amounts of nutrients and sex pheromones. Diatoms primarily reproduce asexually by cell division, but sexual reproduction may become necessary for their survival if the continuous division causes cells to become smaller and smaller. After all, the cells die if they fall below a minimum size. Diatoms also search actively for nutrients they need for the formation of their cell walls. They can trace silicate minerals in their environment and actively move towards this food source.
The decision of one diatom determines the fate of more than a single cell. It affects the dynamics of the entire biofilm, which is composed of communities of countless diatoms. Using mathematical models, the researchers calculated interactions between cell density and the availability of nutrients (silicate minerals) and mating partners (pheromones). Based on these results, the scientists were able to better explain how biofilms are organized.
The team would now like to find out how the single-cell organisms perceive, process, and evaluate chemical signals. "Our goal is to identify the corresponding receptors and signal processing pathways,” Pohnert says, “but this will be a very complex endeavor given the fact that we know so little about these important microalgae.”