Cilia: 'The bouncer' of bacteria

A new paper, from University of Southern California, elucidates the active role of cilia in regulating flow for bacteria filtering and enhancing chemical communication.

The paper, published in the Proceedings of the National Academy of Sciences, describes a framework for the role of fluid mechanics in letting symbiotic bacteria in an organism and enhancing chemical communication between the symbiont and the host organism. The results are contrary to previous research which assumes that cilia solely play a "clearance function." They could shed light on the role cilia -- which are the size of one hundredth of a single human hair -- play in human respiratory system and even in the reproductive systems and the brain. Their findings could also provide insights on how cilia dysfunction within organs affect for example, pulmonary conditions or infertility (how cilia help sperm reach eggs).

To learn about how cilia might work in the human body, Kanso, in collaboration with symbiosis expert McFall-Ngai and biofluid expert Janna Nawroth studied bobtail squid. The researchers examined how these squids in their nascent stage allow symbiotic bacteria Vibrio Fischeri to enter into their ciliated light organs, which play a crucial role in camouflaging the ink sacks of the otherwise translucent organism while they hunt for food at night. The scholars sought to know: why does this bacterium gain access and why do all bacteria fail to accumulate within the squid's light organ? In addition, they sought to explain what, if any, is the role of cilia in allowing access?

Researchers discovered that a vortical or "donut-like" flow generated by the cilia was kicking away most particles. The role of the fluid motion in filtering particles by size was verified using a physics-based mathematical model. One of the core findings was that there were two distinct flows taking place by two different types of cilia. Longer cilia move in a "wave-like" fashion which creates a vortical flow field that filters particles and then shorter cilia which beat randomly keep the particles in place and gently mix the local flow. This random motion by the cilia and fluid mixing enhance the chemical screening of bacteria. To further prove the important role played by cilia, the researchers also found that if cilia are "killed," particles will accumulate everywhere in the organism.

See:

Janna C. Nawroth, Hanliang Guo, Eric Koch, Elizabeth A. C. Heath-Heckman, John C. Hermanson, Edward G. Ruby, John O. Dabiri, Eva Kanso, Margaret McFall-Ngai. Motile cilia create fluid-mechanical microhabitats for the active recruitment of the host microbiome. Proceedings of the National Academy of Sciences, 2017; 114 (36): 9510 DOI: 10.1073/pnas.1706926114

Posted by Dr. Tim Sandle