Microbial teamwork: bacteria observed creating ‘canals’
A study led by a research team from the Department of Physics at the Chinese University of Hong Kong has discovered a surprising form of bacterial teamwork: the bacteria can spontaneously build channel networks for effective delivery of materials across long distances, and have been named “bacterial canals”. The discovery challenges the prevailing belief that long-range material transport in the microbial world is inefficient. It also furthers our understanding of the pathogenic mechanism of bacteria.
Long-range material transport is essential to maintaining the physiological functions of multicellular organisms such as animals and plants. By contrast, material transport in the microbial world is carried out by molecular diffusion, and is often short-range, with low efficiency over longer ranges.
In this study, Professor Yilin Wu and his research team at the Chinese University of Hong Kong discovered this novel form of bacterial teamwork in colonies of Pseudomonas aeruginosa, a bacterium often found in the natural environment and wound infections. They found that a number of open fluid channels, with a width of tens to hundreds of microns, spontaneously develop in a bacterial colony. The fluid channels support the transport of cells and outer membrane with a peak speed of 450 microns per second, more than ten times the typical swimming speed of bacteria.
By using multi-scale microscopy, particle tracking, and physical modelling, the team elucidated the mechanism of bacterial canal formation. They found that the development of bacterial canals is essentially driven by interfacial mechanics and the instability of complex fluids. Bacterial cells can actively produce surfactants, molecules that lower the surface tension of liquids, like those commonly found in cleaning detergents. While the colony becomes a complex fluid consisting of cells and surfactants, the surfactants diffuse away from the colony, leading to a lower surface tension inside the colony than outside. The surface tension difference pulls the colony outwards. During this pulling process, a number of banded flow regions are formed, which become bacterial canals when stable. The team also developed a mathematical model that incorporates the interfacial mechanics, material transport and cell-cell communication to understand the spatial and temporal changes of material transport in bacterial canals.
In collaboration with Professor Liang Yang at the Southern University of Science and Technology in Shenzhen, the team also demonstrated that the bacterial canals help to eradicate competitors of Pseudomonas aeruginosa, such as Staphylococcus aureus, a human pathogen that often causes skin and soft tissue infections and is known for its ability to develop tolerance to multiple antibiotic drugs, with some of its members known as “superbugs”. The study provides a better understanding of the competition or coexistence between pathogenic bacteria, as well as bacterial dispersal during pathogenesis.
“The studies deepen the understanding of living matter physics, and demonstrate that interfacial fluid mechanics can be exploited by primitive lifeforms to drive large-scale material transport," Wu said. "It provides a new strategy to design self-organised functions in synthetic microbial communities, advancing the development of bioengineering, biomaterials and synthetic biology.”
Their findings were recently published in the scientific journal eLife.