Single-Cell Data Sheds New Light on Bacterial Growth Dynamics

Scientists from Washington University and Purdue University have used single-cell data to develop a new framework for understanding the relationship between cell growth, DNA replication, and division in bacteria. In a recent paper published in PLOS Genetics, a team of biologists and physicists used actual single-cell data to create an updated model, which could lead to a better understanding of the behavior of individual cells and the mechanisms behind bacterial growth.

Traditionally, researchers have relied on population-level strategies to understand fundamental aspects of bacterial physiology, describing the behavior of idealized "average" cells. These models have served as the foundation for prevailing models of bacterial growth, but they may not accurately describe how individual cells really work. 

Single-cell live imaging technologies have now made it possible to study individual cells' behavior. The team used data from the model organism Escherichia coli to construct a minimal mathematical model that captured the complex, stochastic behaviors of individual cells and accurately matched individual cell data.

Based on average cell behavior, others had come to view the basic cell cycle steps of DNA replication and cell division as dependent on each other. But the new research found that DNA replication and cell division can occur at different rates within individual cells and are not reliant on each other. As long as mechanisms are in place to prevent division across uncopied chromosomes or fix any issues that arise, the processes can occur independently.

The team also found that cell growth rates can vary significantly between individual cells, as well as influence DNA replication and cell division. These findings could have implications for our understanding of bacterial growth and could inform the development of new strategies for controlling the growth of harmful bacteria.

Petra Levin, the George William and Irene Koechig Freiberg Professor of Biology at Washington University and an author of the paper, explains, "What is true for the average cell is not necessarily true for the individual cell. Bacteria are just like us in this regard!"

Srividya Iyer-Biswas, a physicist at Purdue University and co-author of the paper, adds, "Imagine each bacterium as singing its own whimsical tune, following its own rhythm. The collective - a population of millions of cells - has its own music, where no single voice especially stands out, but a song nonetheless emerges. From hearing just the collective rendition, how could one possibly uncover what precisely an individual's song might be? That is the problem we were faced with."