Animal and human microbiomes are made up of bacteria. They represent a significant class of active matter and are the primary cause of many diseases. Large-scale swarming and turbulent-like motility are observed in concentrated bacterial solutions. Although our understanding of the collective behavior of germs in Newtonian fluids is good, there are still many unanswered fundamental concerns concerning complex fluids.
A new study by scientists at Penn State demonstrates how bacteria use mucus to enhance their ability to self-organize and possibly drive infection. They found that bacteria use mucus to mount a coordinated attack on the immune system. The thicker the mucus, the better the bacteria can swarm.
Scientists performed experiments using synthetic pig stomach mucus, natural cow cervical mucus, and a water-soluble polymer compound called polyvidone. The experiments revealed that bacteria may coordinate their movements more effectively in thick mucus than in liquids.
This study highlights how bacteria colonize mucus and mucosal surfaces. Through this study, scientists also learned how mucus promotes swarming, or collective motion, among bacteria, which may make bacterial colonies more resistant to antibiotics.
This is the first study demonstrating the collective swimming of bacteria in mucus.
Igor Aronson, Huck Chair Professor of Biomedical Engineering, Chemistry, and Mathematics at Penn State and corresponding author of the paper, said, “Mucus is essential for many biological functions. It lines the surfaces of cells and tissues and protects against pathogens such as bacteria, fungi and viruses.”
“But it is also the host material for bacteria-born infections, including sexually transmitted and gastric diseases. According to Aronson, a better understanding of how bacteria swarm in mucus could pave the way for new strategies to combat infections and the growing problem of antibiotic resistance.”
“Our findings demonstrate how mucus consistency affects random motion of individual bacteria and influences their transition to coordinated, collective motion of large bacterial groups.”
“There are studies demonstrating that collective motion or swarming of bacteria enhances the ability of bacterial colonies to fend off the effect of antibiotics. The onset of collective behavior studied in our work directly relates to swarming.”
Because of its liquid-like and solid-like properties, mucus is a challenging substance to study.
Using microscopic imaging techniques, the scientists observed the collective motion of concentrated Bacillus subtilis in both natural cow cervical mucus and synthetic pig stomach mucus to understand better how mucus becomes infected. These findings were contrasted with observations of Bacillus subtilis moving in a water-soluble polymer polyvidone at various concentrations, ranging from high to low polyvidone levels. The experimental outcomes were also contrasted with a computational model of bacterial collective motion in viscoelastic fluids, such as mucus.
The group discovered that the consistency of mucus significantly influences the behavior of bacteria as a whole. The findings showed that the likelihood of the bacteria exhibiting collective locomotion and creating a well-coordinated swarm increased with mucus thickness.
Aronson said, “We were able to show how the viscoelasticity in mucus enhances bacterial organization, which in turn leads to coherently moving bacterial groups that cause infection.”
“Our results reveal that the levels of elasticity and viscosity in mucus are a main driver in how bacterial communities organize themselves, which can provide insight into how we can control and prevent bacterial invasion in mucus.”
“The team expects human mucus to exhibit similar physical properties, meaning their findings are also relevant for human health.”
“The onset of the collective motion of bacteria and their interaction with mucus should be the same as in cow, pig, or human mucus since these substances have similar mechanical properties.”
“Our results have implications for human and animal health. We’re showing that mucus viscoelasticity can enhance the large-scale collective motion of bacteria, which may accelerate how quickly bacteria penetrate mucus protective barrier and infect internal tissues.”
Journal Reference:
- Wentian Liao, Igor S Aranson. Viscoelasticity enhances collective motion of bacteria. PNAS Nexus. DOI: 10.1093/pnasnexus/pgad291