Elife lined up and walked together-from the disordered individual movement of bacteria to the orderly migration of groups

There are a large number of social creatures living in nature.
In order to find more abundant food and a more suitable environment, they often need to migrate in groups
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This requires that all groups of people, whether men, women, young or old, and in good or bad physique, must maintain the same speed of migration to prevent dangers caused by orders
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However, different individuals always have differences in mobility and navigation capabilities, so a robust speed coordination mechanism is essential for a group
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Intelligent creatures can use language commands and other methods to transfer information between individuals
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But for single-celled organisms such as bacteria, their available information transmission methods are extremely limited.
What kind of mechanism can ensure the collective migration of bacteria with different abilities? On November 2, 2021, Fu Xiongfei's research group from the Institute of Synthetic Biology, Shenzhen Advanced Institute of the Chinese Academy of Sciences published an article Spatial modulation of individual behaviors enables an ordered structure of diverse phenotypes during bacterial group migration, revealing that bacteria pass through an ordered queue Realize the coordination mechanism of cluster migration [1]
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At the same time, the paper was selected as the "eLife digest" scientific digest review report
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As the smallest living organism that can move independently, bacteria can rotate the flagella on the body and swim in the liquid
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At the same time, they can randomly change the direction of swimming by rolling their bodies from time to time
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Under the attraction of some chemical substances (we usually call chemical substances with attractive ability as chemotaxis), bacteria can move randomly in all directions while slowly approaching the direction of higher concentration of chemotaxis by adjusting the frequency of body tumbling.

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However, the sensitivity of different bacterial individuals to chemotaxis is different, some can accumulate to high concentration areas faster, and some are slower [2]
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Figure | Schematic diagram of the difference between the random walk and chemotactic ability of bacteria
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 Provided by: Cai Zhuoran and Wu Wei of the research team
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When bacteria form a group and gather together, they will consume the chemotaxis in the environment together
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With the gradual consumption of local chemotaxis, they will rely on their chemotaxis ability to swim towards territories they haven't been to and enjoy the higher concentration of chemotaxis there
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Interestingly, in such a migrating group, although bacteria that are not sensitive to the concentration of chemoattractants are at the end of the group, they are not left behind.
Instead, they closely follow the sensitive bacteria to form a compact structure.
Sequence queue, moving together at the same speed
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Previously, Fu Xiongfei’s laboratory and Thierry Emonet’s laboratory at Yale University collaborated to find that such an ordered queue is essential for the migration of bacterial colonies [3]
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However, the movement of individual bacteria is always changing the direction of swimming.
How does such an ordered group of marching queues emerge from the random movement of disordered individuals? In order to answer this question, the researchers tracked and observed the trajectory of each bacteria
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They found that every bacteria reciprocates in the group: when the bacteria fall behind the group, they will swim harder; once they swim at the front of the group, they will swim around like they have lost their navigation.
, Until it fell at the back end of the group, struggling forward again
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This kind of exercise is as if there is a kind of force pushing them forward.
If you fall behind, you can push them, and you don't care if you run to the front
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After a series of model deductions, the researchers found that this kind of'power', which is strong at the back and weak at the front, does exist, and it is precisely because the concentration gradient generated by the bacterial population that consumes chemotaxis is always high at the back and low at the front
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Therefore, when the bacteria fall at the back end of the colony, they will be more attracted by the chemotaxis, making the bacteria work harder to swim forward
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When they swim to the front of the group, because the chemotactic concentration is similar everywhere, they lose the motivation to move on
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 Figure | Schematic diagram of bacterial movement behavior characteristics in different spatial positions in the population
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Provided by: Cai Zhuoran and Wu Wei of the scientific research team, when the bacterial colony migrates, there is such a strong'pushing force' at the back and weak at the front, which is a huge benefit for those less sensitive bacteria
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Because whenever they are left behind by those companions who are sensitive to chemotaxis, they will be given greater impetus to drive them forward
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Those individuals who swim in front of them are lost in the direction of continuing to swim in the high-concentration chemotaxis'comfortable' environment
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Of course, it is precisely because of this mechanism that individuals with different abilities can coexist in a coordinated manner in the same group and move forward at the same average rate
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Furthermore, the researchers used synthetic biology methods to artificially regulate the sensitivity of bacteria and successfully verified the role of this coordination mechanism
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This research has shown us a simple and robust group coordination mechanism: as long as a driving force is established in the group that is strong at the back and weak at the front, it is possible to ensure that individuals with different abilities can advance at the same rate
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It can not only explain the group migration behavior of many living organisms, but also provide a reference for the more complex group collaboration of human society
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 Figure | Schematic diagram of bacteria forming an ordered queue
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 Provided by: Research Team Chen Qian, Cai Zhuoran, Wu Wei
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Bai Yang, an assistant researcher at the Institute of Synthetic Biology, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, and doctoral student He Caiyun are the co-first authors of the paper, and researcher Fu Xiongfei is the corresponding author of the paper
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Original link: https://elifesciences.
org/articles/67316 References[1] Bai, Y.
, He, C.
, Long, J.
, Li, X.
, & Fu, X.
(2021).
Spatial modulation of individual behaviors enables an ordered structure of diverse phenotypes during bacterial group migration.
eLife 2021;10:e67316[2] Dufour, YS, Fu, X.
, Hernandez-Nunez, L.
, & Emonet, T.
(2014).
Limits of Feedback Control in Bacterial Chemotaxis.
PLoS Computational Biology, 10(6).
[3] Fu, X.
, Kato, S.
, Long, J.
, Mattingly, HH, He, C.
, Vural, DC, Zucker, SW , & Emonet, T.
(2018).
Spatial self-organization resolves conflicts between individuality and collective migration.
Nature Communications, 9(1).
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