Authorized by the author of the journal of the Berger International Society of System Microbiology, a well-known bacteriological research expert in China, Professor Liu Shulin from Harbin Medical University wrote an article and first proposed the "3C" standard for defining bacterial species. With this "3C" standard, people are expected to re-examine the bacterial species identified or to be determined by the previous standards that humans have passed so far. The most direct social significance is to guide clinical diagnosis and treatment.
In 1684, a Dutch glasses merchant observed some "tiny animals" for the first time through a self-made microscope. This was the first time that "bacteria" were seen in human history. Over the past 300 years, people have discovered tens of thousands of bacteria in succession. Most of these bacteria are non-pathogenic, and only a few can cause diseases in humans, animals, or plants. Therefore, one cannot help asking how to classify bacteria and classify different bacteria into species to distinguish them from other "species" (that is, "species" in taxonomy)?
Over the years, countless scientists have tried to establish different methodologies and use different technical methods to classify bacteria, and have introduced a series of standards, some of which are still used by people today, but these methodologies themselves have more or less defects. And deficiencies. For example, in the 1970s, when people used whole-genome DNA-DNA hybridization, and their DNA exchange rate reached more than 70%, it was considered a "species". This method is still used by people until today. The classification method currently accepted by the scientific community is that the similarity of 16SrRNA is more than 97%, and the DNA-DNA hybridization recombination rate is greater than 70%.
In many years of scientific research practice, Liu Shulin believes that this method is not ideal. He pointed out that the sequence similarity and DNA recombination rate of 16SrRNA have no obvious limits in bacteria, and 70% and 97% are artificially defined, lacking scientific reason, and can not clearly classify bacteria. Therefore, for many years he has been devoted to the intensive discussion of bacterial taxonomy, and recently proposed the "3C" standard of bacterial taxonomy for the first time in the world, namely: 1. All members of the same species are closely related; 2. Closely related but There are clear genetic boundaries between different species; 3. All members of the same species have common biological characteristics, and these characteristic biological characteristics are not found in any other species. The English expressions of these three standards all begin with the English letter C, so they are named "3C" standards.
In this regard, Liu Shulin took Salmonella as an example to explain the "3C" standard. For more than a century, Salmonella has been widely studied by academics as an important pathogen. These bacteria can cause disease and even death in humans and animals. However, the classification method for Salmonella is still inconclusive. Salmonella typhimurium, which causes human typhoid fever, and Salmonella typhimurium, which can only cause gastroenteritis, are considered to be subspecies of Salmonella enteritidis.
According to the "3C" standard, Professor Liu confirmed that Salmonella typhi and Salmonella typhi were not "brothers". From the pulse field analysis data, he found that the results of enzyme digestion of Salmonella typhi and Salmonella typhi were significantly different, while the different strains of Salmonella typhi or Salmonella typhi were very similar. On the other hand, from the results of genome sequencing, it is also found that there is a large sequence difference between Salmonella typhi and Salmonella typhimurium. Finally, they each have different evolutionary history, pathogenicity, host range, and genomics characteristics. After experimental verification, the frequency of DNA exchange between these two bacteria is also very low. It was concluded that Salmonella typhi and Salmonella typhi should not belong to the same species of bacteria.
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