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

## TL;DR

This paper introduces a new image analysis tool to study cell shape variation in dense bacterial swarms, revealing unexpected diversity during collective movement.

## Contribution

The paper introduces Swarmetrics, a novel image analysis pipeline for unbiased morphometric analysis of densely packed microbial communities.

## Key findings

- Swarmetrics detected unexpected heterogeneity in cell length during Proteus mirabilis swarm development.
- Cell length variance reliably indicated swarm development stages, comparable to gene expression markers.
- The findings challenge the traditional view of uniform transitions in bacterial swarming behavior.

## Abstract

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.