Bacterial migration: Darwin’s set didn’t work anymore

Many people regard Darwin’s “things to choose, the survival of the fittest” as a tribute, but others do not believe in biological evolution and later social Darwinism. At least, it doesn’t fully explain how the world works.

Bacterial migration: Darwin's set didn't work anymore

Photo Liu Chenli’s team from left to right: Li Dengjin (co-author), Liu Chenli (communications author), Liu Weirong (co-author).

Bacterial migration: Darwin's set didn't work anymore

Bacterial migration: Darwin's set didn't work anymore

Bacterial migration: Darwin's set didn't work anymore

Cartoons by the Shenzhen Institute of Advanced Technology of the Chinese Academy of Sciences

For example, how does the 40 trillion cells that divide a fertilized egg form the tissue organs in an orderly manner and eventually develop into a complete human body? How do hundreds of creatures in the same forest preempt their living space to form complex and stable ecosystems? Although evolution points out the evolutionary law and development direction of life, the principle of “on-demand manufacturing” of multicellular organisms is still a puzzle, and the diversity of species in the same environment is difficult to be explained by a “choice of things”.

Now, scientists have found a counterexample: the migration of bacteria in the microcosm. The research team led by Liu Chenli, a researcher at the Shenzhen Institute of Advanced Technology of the Chinese Academy of Sciences and the Shenzhen Institute of Synthetic Biology Innovation, and a team of researchers from the University of California, San Diego, found that in the process of bacterial migration, it was not “fast” and “slow” to eliminate. Instead, each organism corresponds to an optimal expansion rate and strategy, from which a quantitative formula for the evolution of biological migration is worked out to explain biodiversity and provide tools for future “creations”.

Not long ago, this is considered a “major breakthrough in basic research” and was published in a long-form form in the international academic journal Nature. Zhao Guoping, a member of the Chinese Academy of Sciences and a researcher in the Key Laboratory of Synthetic Biology of the Chinese Academy of Sciences, commented that the law revealed by this original innovation work is of irreplaceable significance for the evolution of species, especially the theory of microevolution within species, and is also a vivid example of experimental evolution research.

“Grabbing the land” doesn’t just rely on “running fast”

The Great Migration of African Animals is a great wonder of nature, and every year millions of animals are divided into the former and the latter “three armies” northwards: the first, is more than 200,000 wild zebras, followed by a million horned horses, after the temple, is 500,000 gazelles. During this period, 400,000 new lives have been added to the team.

“Moving into” the lab, replacing animals with bacteria and putting them in petri dishes became the subject of Liu Chenli’s team’s research – the bacterial migration.

Liu Chenli told reporters that according to the traditional research results, in order to cope with changes in the environment, biological migration through migration to obtain nutrition or new living environment, in the migration process in the forefront of the biological, with the right to choose, can choose delicious food, but also priority occupation of a piece of territory, it seems that “the sooner the better” is the optimal survival strategy.

Accordingly, in the competition for bacterial migration, the desire to occupy the largest territory is also the expansion rate “the sooner the better”, different bacteria “run alone” case is true.

However, when different bacteria “run at the same time”, something unexpected happens.

In the early experiments to explore bacterial migration, Liu Chenli’s team designed four culture environments, in each environment repeatedly “interpreted” the bacterial migration process, each repeating 50 cycles, the researchers were surprised to find that: the migration rate of the bacteria group is scattered changes, occupying the peripheral flora more “run” faster, while occupying the center of the bacteria group, it is slowing down. Footsteps.

The results show that not only “fast bacteria” have advantages, “slow bacteria” also found their own living space.

“This phenomenon is unexpected, in the homogenous environment, it is generally believed that ‘first come, first-come’, slower’ means to be eliminated, previous research in the field also did not notice that ‘slow movement’ has its advantages.” Liu Chenli believes that these phenomena show that bacteria in the space expansion process, not only the “speed up the movement” strategy, but also other factors determine the “final map” distribution.

Ouyang Yu, a member of the Chinese Academy of Sciences and a professor at Peking University’s Center for Quantitative Biology, was pleased to hear the results, which, in his view, took a big step forward in quantitative and systematic research on “time domain” and “airspace” for microecological evolution.

“In the absence of quantitatively controlled experiments, Darwin’s theory of evolution was unable to develop a theory capable of making quantitative predictions and was therefore incomplete. Especially in the environment of complex space-time change, the competition and adaptation strategy of multi-species is more difficult in the study of evolutionary theory. Ou Yang said.

Today’s achievement is clearly a breakthrough.

Using basic life parameters such as bacterial migration and reproduction, the results examined the ability of different bacterial populations to settle, grow and reproduce in different territories, as well as the evolutionary patterns of resilience, “as is commonly believed, ” Ouyang said. The first-come, first-come-and-first-year’ strategy is different, with the bacteria with the strongest planting capacity in a particular territory not being the fastest, but with an optimal expansion rate in different territories. “

“Exposed” migration law in the battle of bacteria

More importantly, Liu Chenli’s team did not stay on the surface of the phenomenon, but continued to go down to the theoretical explanation.

After they saw the results of the “first-come, no-first-served” experiment, which was counterintuitive and common sense, the team derived a simple quantitative relationship using nonlinear dynamics models: through the classic “two-to-two competition” experiment and mathematical model analysis, they found the spatial size and regional location of a population. There is a clear quantitative relationship with the migration rate of its competitors.

Liu Weirong is a doctoral student of Liu Chenli and the first author of this paper. He told reporters, in order to find out the bacteria “attack” the key factors and common law, the scientific research team in the later design of “two competition” experiments, so that the movement speed of the two bacteria, at the same starting point “simultaneous expansion”, the result, is still surprising.

A very special watershed emerged.

Specifically, after the departure of the two flora, the spatial distribution of the number of bacteria, gradually appeared a turning position, where the two sides “equal strength.” In the space within this position, the “slow running” flora has the advantage, once beyond this position, “run fast” bacteria to win quickly.

Subsequently, the scientific research team will be “bacterial war” experiments, extended to 3 bacteria, the result formed two watersheds, from slow to fast movement of different bacteria, from the inside out each occupied the advantage of space.

Liu Weirong told reporters that after 5 groups of evolutionary bacteria and synthetic biology modified bacteria complex repeated competitive experiments, the results show that this phenomenon is universal.

She recorded this situation, the team concluded that: in the entire process of bacterial migration, each microbiome has its own “expansion strategy”, according to the space area and location that she wants to occupy, to regulate the pace of their migration, and ultimately constitute a stable pattern of “one each.”

After finding the law of migration evolution, Liu Chenli’s team derived quantitative formulas based on model calculations and experimental verification, including the three key factors of survival area, motion speed and growth rate. According to this formula, scientists can work out the optimal strategy for migration evolution, given the known size of space.

“This beautiful work demonstrates the simple quantitative relationship behind complex biological processes. Ouyang said: This bacterial population of territory competition, can be considered a space “game game”, as the gamer’s bacteria, the migration rate as a strategy, migration rate stable equilibrium state, similar to the nash equilibrium in game theory, that is, any player deviated from this stability strategy, will not get any benefit.

“Creation” technology has been given powerful tools

“This provides a enlightenment for explaining the emergence of species diversity under the same ecological environment. Liu Chenli said that most of the previous ecological theories believe that the ecological environment is different, is the cause of species diversity, and now this quantitative law, it reveals different species, according to different growth speed and speed of movement, to seize their own survival space mystery.

More importantly, this law has made more possibilities for synthetic biology, the “creation” technology that has emerged in the 21st century.

Liu Chenli told reporters, “If synthetic biology is like ‘Lego’, the assembly of biological structures, then the quantitative formula obtained by this study, for the ‘creation’ project provides a new design theory.” “

The so-called synthetic biology is the use of engineered design concept, through the design, transformation and synthesis of organisms, the creation of artificial life system. In the sci-fi film Jurassic Park, scientists used the blood of dinosaurs retained in natural amber to extract techniques such as repairing the molecular structure of DNA to develop extinct dinosaurs – a seemingly advanced life science concept known as a “film version” of synthetic biology.

“The laws of gravity, thermodynamics… There are many laws in the physical world. And we believe that the biological world also exists quantitative law, understand the quantitative law, can really realize the engineering of biology, and finally achieve the creation of knowledge, creation. Liu Chenli said.

In his view, this time the biological migration evolution law obtained from bacteria could theoretically guide the construction of multicellular organisms or ecological systems. In the future, under the guidance of this theory, the engineering synthesis of biological tissues and organs can be achieved by regulating cell movement and growth speed and quantitatively calculating the distribution of cells in space.

Zhao Guoping agrees, in his view, the traditional experimental evolution of bacteria, usually only thinking about time information, and this work, specifically to examine why the population can be spatially competitive planting, and to analyze the evolution of the genome in this certain planting process.

“This study shows that bacteria are not only a great material for quantitative and synthetic biology research, but also a great material for experimental evolutionary research. Zhao Guoping said, unfortunately, there are not many laboratories engaged in this area of research.

The reason for this is that, on the one hand, researchers need to have a deep theoretical knowledge of genetics and evolutionary science, and on the other hand, the success of such work requires quantitative analysis and theoretical model prediction on the basis of a large and long-term and repetitive and accurate measurement. Zhao Guoping hopes that this starting point can inspire researchers engaged in basic research in life sciences in China, especially young researchers, to expand their research horizons and boldly innovate ideas.

He said that life science research is beginning a new era of “multidisciplinary convergence” research characterized by systematic, quantitative and engineering, and is gradually moving from the description stage to the construction altogether through the analytical stage, and finally achieving the goal of “predictable, regulated and creative” of life and life processes.

“In this process, an important scientific issue is to obtain a quantitative understanding of the principle of the orderly structure formation of biological systems. Zhao Guoping said. Now that has happened, but it is only the beginning.

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