Are bacteria big or small? Scientists challenge two major rules to come up with new formulas

On May 18, nature microbiology, an international authoritative academic journal, published a paper from Liu Chenli's laboratory at the Shenzhen Institute of Advanced Technology of the Chinese Academy of Sciences and the Shenzhen Institute of Synthetic Biology Innovation, entitled "The General Quantitative Relationship Between E. coli Cell Growth and Cell Cycles".
The study, using E. coli as a model organism, debunks the factors that make up the size of bacteria, deduces a new "individual growth division equation", revises the two original growth laws in this field, and provides the basic principles of construction for the rational design of living organisms in the field of synthetic biology. Bacteria are the single-celled organisms with the widest distribution and the largest number of individuals in nature. From Lactobacillus lactic acid, which ferments yogurt, to E. coli, which produces insulin, bacteria fill every aspect of human life and scientific research.
each bacterium has a variety of inheritable sizes, and these tiny cells can sometimes vary in size by 106-108 times. The team points out that the size of the bacteria is not only diverse, but also stable. Bacterial cells in these environments remain at a specific size, even at hydrothermal mouths above 100 degrees, salt lakes with salt concentrations of up to 5 moles, and ion radioactivity greater than 1,000 times the lethal dose of humans. Bacterial cells of different sizes.
In the field of modern quantitative microbiology, "SMK growth law" is the first quantitative law to be discovered, complementing the "constant starting mass hypothesis", and forming a research thinking paradigm that has dominated the research field related to bacterial cell cycles for more than half a century. In order to explore the mechanism of bacterial cell division, Liu Chenli's team validated two major rules.
Liu Chenli's team spent more than 3 years selecting more than 30 media to conduct experiments, which is by far the most widely used media species and covering the widest range of growth rates in similar studies reported. After hundreds of samples and thousands of quantitative measurements, the life cycle of bacterial cells became clearer. Dr. Zheng Hai, the first author of the paper, said, "At low growth rates, it takes up to a week to complete an experiment, and to ensure reliable data, the experiment needs to be repeated more than nine times." The
study showed that although the average size of cells increased with the growth rate, the data did not conform to the quantitative formula proposed by the "SMK Growth Law", and the study found that the hypothesis that the constant ratio before cell DNA replication is not static, but rather shows a trend of up and down based on the increase in growth rate. This suggests that the two major laws in the field of modern quantitative microbiology may not be accurate.
Liu Chenli said, "According to the law, regardless of the growth of cells, once the 'starting mass', should start a new round of DNA replication, however, we have observed in the experiment, bacterial cells do not follow the hypothesis, under different culture conditions, 'starting mass' has highs and lows." "
if the two laws are not accurate, how is the size of the bacteria determined?" To answer this scientific question, Liu Chenli's team eventually developed a new "individual growth division equation" that applies to different growth rate conditions by looking for quantitative relationships behind a large amount of scientific experimental data. The equation of individual growth division.
The new equation harmonizes the mechanism of bacterial cell cycle regulation under different growth rate conditions, and the proposed quantitative formula also makes natural phenomena such as bacterial individual size and growth rate predictable, for example, when the bacterial growth rate and DNA replication cycle are known, the size of bacteria can be accurately predicted. The division equation provides researchers with new research paradigms and thinking methods to answer the relationship between bacterial cell size and DNA replication cycle and growth rate, and has a wide range of applications.
does the "individual growth equation" mean to understand the control mechanism of bacterial cell cycles? Under the constraint of "individual growth equation", the research team discussed the control mechanism of bacterial cell division. On this basis, a completely new molecular mechanism hypothesis is proposed, which holds that there is a "splitting permit" which is related to "cell growth" and "chromosomal replication separation". When it accumulates to a certain threshold, the cells divide. On this basis, the research team established the corresponding mathematical model, and further experiments did verify the theoretical prediction.
it is worth mentioning that, in Liu Chenli's view, the ultimate goal of synthetic biology is to achieve rational design, transformation of existing life forms or creation of new life forms to meet the different needs of mankind. Led by "synthetic biology," Liu Chenli's team last year also revealed the migration formula for bacterial populations.
this study once again confirms the importance of quantitative thinking in life science research, and every operating rule we find is an attempt to find 'drawings' that can be used to guide the design, transformation, and reconstruction of life forms. Liu Chenli said.