This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: A new study led by researchers from Ben-Gurion University of the Negev (BGU) reveals that living matter violates previously known physical principles of symmetry when cellular flows form and break down collective patterns. The research, published in Nature Physics, challenges conventional liquid-crystal physics by showing that moving single-celled bacteria and human respiratory cells spontaneously break mirror symmetry, moving in curved, irreversible spiral paths.
The collaborative study was led by Professors Avraham Be'er and Victor Yashunsky from BGU's Jacob Blaustein Institutes for Desert Research (Sede Boqer Campus) and Department of Physics, alongside Professor Gil Ariel from Bar-Ilan University and Professor D. Pearce from the University of Geneva. In physics, collections of rod-shaped objects naturally align and flow together like liquid crystals.
Bacteria and cells, which can move themselves, form a state known as an "active nematic." Within these flowing swarms, natural disruptions called topological defects constantly form in pairs. While they look like the loops and whorls of a permanent fingerprint, these active twists are constantly moving, circulating through the swarm until they collide and cancel each other out. Standard physical theories predict that in active nematic systems, these paired defects should approach and separate along straight, perfectly mirrored lines.
However, by observing two vastly different biological systems across distant evolutionary boundaries—fast-swarming Bacillus subtilis bacteria and slow-crawling human bronchial epithelial cells—the researchers discovered that living systems break these physical expectations: To bridge the gap between biological matter and synthetic physics, the team developed an active "nemato-polar" model. It accounts for how self-propelled cells burn chemical fuel to drive directional motion—introducing polar self-propulsion into a nematically ordered system. When this directional self-propulsion is layered onto liquid-crystal alignment, it spontaneously creates an internal clockwise or counterclockwise twisting torque right at the core of the pattern disruption.
This active rotational force pushes the defects into a permanent spiral trajectory from the moment they are born until they collide and disappear. Understanding how living cells organize these collective flow patterns provides insight into fundamental biological processes. In nature, these physical dynamics govern how bacterial colonies coordinate to form resilient, drug-resistant biofilms and how epithelial tissue layers direct cellular traffic to close wounds during tissue repair.
"Our findings demonstrate that the self-propelling nature of individual cells fundamentally reshapes collective behavior at larger scales," the researchers note. "By uncovering how microscopic motion imprints unexpected symmetries onto tissue and bacterial dynamics, this study introduces a new physical framework for understanding how living communities self-organize." A. Be'er et al, Irreversibility and symmetry breaking in the creation and annihilation of defects in active living matter, Nature Physics (2026).
Extract — continue reading at the source.
