Population heterogeneity revealed in morphometric analysis of densely populated microbial swarm collectives

Uncovering cell morphology within communities is crucial to understanding how collective groups of organisms can function and adapt to their environments. Key questions remain regarding how cell morphology influences population behaviors and whether uniformity is required for coordinated actions, such as collective migration. These gaps hinder the ability to describe how individuals contribute to collective adaptability and coordinated behaviors. We developed an image capture and analysis pipeline, named Swarmetrics, for studying individual cells that are within dense bacterial communities, can participate in collective behaviors, and may have irregular cell morphologies. We used Proteus mirabilis swarms as a proof of concept. Swarmetrics achieved an unbiased analysis of most cells, even those that were unlabeled and in a densely populated environment. In P. mirabilis swarms, we found unexpected heterogeneity in cell length throughout the swarm development cycle, particularly during active collective migration. Variance in cell length was revealed to be a reliable indicator of swarm development stage, comparable to a gene expression marker. These findings questioned the traditional view of uniform or synchronized transitions in bacterial swarming for the Proteus species. This study introduces new tools and insights for studying cellular variation in complex microbial environments, with broad applications to other dense communities, and sheds light on the physiology of individuals during collective behavior.

Understanding how individual cell morphology shapes collective behavior is crucial for uncovering principles of organization across biological systems. We developed an image analysis pipeline, Swarmetrics, and revealed unexpected phenotypic heterogeneity among cells during bacterial collective migration. These results raise questions about the necessity and impact of uniformity-in shape and behaviors-during bacterial collective actions. Swarmetrics also opens the door for quantitative analysis of irregularly shaped cells in dense communities.