New paper by USC Viterbi School of Engineering Professor Eva Kanso and Professor Margaret McFall-Ngai of the Pacific Biosciences Research Center at the University of Hawaii elucidates the active role of cilia in regulating flow for bacteria filtering and
Imagine a club scene--a bouncer at a velvet rope selects which individuals get into the club. This, explains Eva Kanso, a professor of mechanical engineering at USC Viterbi School of Engineering, is what cilia do in an organism.
The squid's internal light organ features several different populations of cilia (green/blue) that coordinate their beating activity to recruit symbiont bacteria from the seawater and facilitate their migration to the pores (right side), where they enter the organ for life-long colonization.
Credit: Lab of Margaret McFall-Ngai, Pacific Biosciences Research Center at the University of Hawaii
Kanso applied the analogy to explain her new paper, "Motile cilia create fluid-mechanical microhabitats for the active recruitment of the host microbiome," co-authored with researchers from the Pacific Biosciences Research Center at the University of Hawaii at Manoa and from Stanford, to explain the active role that cilia have in ensuring certain bacteria are kept out of an organism while other symbiotic bacteria are selectively permitted to enter.
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?
Kanso and McFall-Ngai with lead authors Janna Nawroth, a principal investigator at Emulate Inc, and Hanliang Guo, a PhD student in Kanso's lab at USC, put the squid under a microscope and then exposed it to water containing Vibrio Fischeri bacteria. The process mimicked what happens in nature: the bacteria ended up in the correct spot within the squids' light organs.
To determine if cilia were passive or active within this process, the researchers needed to understand if the bacteria swam into the ink sack or in fact were helped by other structures and processes within the squid host. The researchers then repeated the same experiment without live bacteria--but with particles of the same size as the bacteria, namely one micron in diameter. What they found was that the particles accumulated in the same spot--demonstrating that a physical mechanism in the host (the squid) was at play.
The second phase of experiment then included larger particles (about 4 microns). One might have presumed that the larger particles would have a greater probability of contact with the light organ--but they didn't. This indicated that direct interception was not the dominant mechanism for particle capture and that some other factor was at play. The researchers set out to examine the role of the fluid flow generated by the cilia in filtering particles.
Upon further investigation, Kanso and Nawroth 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 developed by Kanso and Guo. Kanso describes the role that cilia seemed to be playing as a "mechanical gate."
The researchers then mapped out the ciliated surface of the whole light organ and the flow field it generates. 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.
Kanso and her collaborators are now developing a microfluidic platform to test the response of Vibrio Fischeri to distinct flow and chemical signals presented by the ciliated light organ of the host. This platform will be used as a research tool to investigate the relative importance of each of these signals in the recruitment of bacteria to ciliated surfaces.
Ian Chaffee | EurekAlert!
One step closer to reality
20.04.2018 | Max-Planck-Institut für Entwicklungsbiologie
The dark side of cichlid fish: from cannibal to caregiver
20.04.2018 | Veterinärmedizinische Universität Wien
University of Connecticut researchers have created a biodegradable composite made of silk fibers that can be used to repair broken load-bearing bones without the complications sometimes presented by other materials.
Repairing major load-bearing bones such as those in the leg can be a long and uncomfortable process.
Study published in the journal ACS Applied Materials & Interfaces is the outcome of an international effort that included teams from Dresden and Berlin in Germany, and the US.
Scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) together with colleagues from the Helmholtz-Zentrum Berlin (HZB) and the University of Virginia...
Novel highly efficient and brilliant gamma-ray source: Based on model calculations, physicists of the Max PIanck Institute for Nuclear Physics in Heidelberg propose a novel method for an efficient high-brilliance gamma-ray source. A giant collimated gamma-ray pulse is generated from the interaction of a dense ultra-relativistic electron beam with a thin solid conductor. Energetic gamma-rays are copiously produced as the electron beam splits into filaments while propagating across the conductor. The resulting gamma-ray energy and flux enable novel experiments in nuclear and fundamental physics.
The typical wavelength of light interacting with an object of the microcosm scales with the size of this object. For atoms, this ranges from visible light to...
Stable joint cartilage can be produced from adult stem cells originating from bone marrow. This is made possible by inducing specific molecular processes occurring during embryonic cartilage formation, as researchers from the University and University Hospital of Basel report in the scientific journal PNAS.
Certain mesenchymal stem/stromal cells from the bone marrow of adults are considered extremely promising for skeletal tissue regeneration. These adult stem...
In the fight against cancer, scientists are developing new drugs to hit tumor cells at so far unused weak points. Such a “sore spot” is the protein complex...
13.04.2018 | Event News
12.04.2018 | Event News
09.04.2018 | Event News
20.04.2018 | Physics and Astronomy
20.04.2018 | Interdisciplinary Research
20.04.2018 | Physics and Astronomy