A Cell So Minimal That It Challenges Definitions of Life

Summary

“The diversity of archaea and bacteria that appear to belong to these supergroups of parasitic organisms is very, very large,” she said. For bacteria, it may be between 25% and 50% of the group’s total share of species, she suggested. The discovery pushes the boundaries of our knowledge of just how small and simple cellular life can become, as it evolves even into forms that are barely alive. An Extraordinary Discovery Nakayama has built a scientific career out of looking more closely than other researchers typically do. He considers an already tiny cell and wonders: Are there even smaller cells that make a home there? “The difference [in size between parasitic and host cells] can sometimes be like that between a human and Godzilla,” Nakayama said. He is fascinated by the potentially vast amount of undiscovered biodiversity these relationships might contain, and his lab looks for such relationships in seawater. The ocean is a nutrient-poor environment that incentivizes cells to form trading partnerships. Sometimes they float along together, loosely tethered, exchanging rare nutrients and energy. Other times their arrangements are more organized. The difference [in size between parasitic and host cells] can sometimes be like that between a human and Godzilla. Takuro Nakayama, University of Tsukuba Citharistes regius is a globally widespread single-celled dinoflagellate that has a walled, pouchlike external chamber for housing symbiotic cyanobacteria. Nakayama and his team searched for the alga by scooping seawater samples from the Pacific Ocean using a fine-mesh net. A common technique is to sequence whatever DNA can be found in the soup of such a sample, an approach called metagenomics. “That method is incredibly powerful for capturing a broad overview,” Nakayama said. “However, with such data, it is often difficult to maintain the link between a sequence and the specific cell it came from, and rare organisms can be easily missed.” His team’s more targeted approach ...