Bacteria are the most widely distributed, smallest and most diverse organisms on the earth, and it can be said that in almost every corner of the earth, at every moment of our daily lives, there will be bacteria.
Usually, as a kind of microorganism, bacteria are very small, and it is difficult to detect their presence with the naked eye, and can only be seen with a microscope. Recently, scientists in the United States have broken this traditional cognition, and the bacteria found are obviously much larger, not only clearly visible with the naked eye, but also up to 2 centimeters in diameter, which simply subverts our understanding of the concept of microorganisms!
Record-breaking giant bacteria
Previously, the largest bacteria discovered by scientists, discovered in Namibia in 1999, was named "Namibia's sulfur pearl", its form is a string of white beads, some individuals can reach 0.75 mm, almost can be distinguished with the naked eye. For the next 10 years, this single-celled bacterium, with its unusual "size", held the record for the world's largest bacteria.
This situation was broken in 2009. Scientists have found a giant bacterium about 1 centimeter in diameter on a small island in the central Caribbean Islands of North America, named "Orthiopodium ornithus" (Orthiopodium). The bacteria were first discovered, and when they were discovered, they were quietly lurking on a rotten leaf in a salty body of a red mangrove swamp. Scientists are extremely excited after discovering this bacterium, on the one hand, it shows that the Caribbean region should hide more things that people did not know before, and on the other hand, such a large bacterium will directly impact people's definition of microorganisms.
In the past 13 years, scientists have come to this water again, taken some water samples from the water, and then want to carry out microbial culture experiments. Unexpectedly, in the samples collected, there were some white vermicelli-like things floating on them, which were thought to be some plant pollen or other impurities contained in the samples. Later, through a series of processes such as fluorescence, X-rays, electron microscopy and genome sequencing of water samples, and finally studied and analyzed, it was found that these fan-like objects were not interfering impurities at first, but solid single-celled organisms.
The bacterium is 2 centimeters long, twice the size of the largest bacterium discovered 13 years ago, more than 1,000 times larger than other typical bacterial "size," and even larger than the body cells of fruit flies. This bacterium is named T. Magnifica, identified as the same genus as the giant bacteria discovered 13 years ago, can be said to be a close relative. The researchers rejoiced in the discovery: "Discovering this bacterium is like meeting a person as tall as Mount Everest." ”
Is this giant bacterium still a "bacterium"?
Many biologists say the discovery of this new giant bacterium has led to a growing recognition that there is unimaginable complexity and diversity in the microbial world, and that the bacterial "family" will have complex structures and genetic adaptability that we did not know before, so that they can grow to unexpected cell sizes.
Some biologists say that in the traditional cognition, the concept of microorganisms describes those tiny organisms that are invisible to the naked eye, and this new discovery will make us re-examine the concept of microorganisms, and we should no longer simply identify bacteria as microorganisms, which seems to be outdated.
From the biological classification point of view, bacteria belong to prokaryotes, and like the animals, plants and fungal organisms around us, their cells belong to "eukaryotic cells", and the most obvious difference between prokaryotes and eukaryotes is that there is no nucleus in their cells, that is to say, there is no "compartment" where DNA genetic material is stored separately.
The discovery of the new giant bacteria also breaks the understanding that the bacteria belong to prokaryotes, because the genetic material of this giant bacteria is wrapped in a similar layer of "inner membrane". If you don't reduce these giant bacteria to prokaryotes, you also pose a problem, that is, they are indeed made of only one cell. To solve this problem, either the definition of bacteria needs to be changed, or the definition of prokaryotes needs to be changed, which is subversive anyway.
Why did it grow so big?
For a long time, scientists believe that single-celled organisms can not grow to a large, because the larger the cell, in order to maintain the physiological activity of the cell, it is necessary to absorb enough energy and nutrients, so that the surface area will increase, when it reaches a certain level, it will no longer be able to support enough energy and nutrient absorption, storage and transformation space. And as the cell volume increases, its internal ATP, the most direct source of energy acquisition, will become extremely difficult to transmit.
However, T. magnifica, a giant bacterium, in many ways has broken the traditional cognition of the above people, its cell structure is "deliberately" divided into a lot of relatively independent "compartments", each "compartment" is performing different functions, equivalent to a cell on the basis of a number of independent and coordinated "subcellular", so as to break through the larger volume, larger surface area of the cell function of many restrictions.
What is more specific is that the DNA genetic material of this cell is "protected" in the "compartment" composed of membrane binding, and this genetic material in the core area alone is almost as large as a melon seed. This isolated genetic material and its structure blurs the distinction between bacteria and eukaryote cells, ensuring more effective control over the body and the complexity of the body's structure. It is this structure that makes T. The number of genes in the magnifica bacteria exceeds 11,000, which is several times more than that of ordinary bacteria.
The above is about the internal reasons why this bacterium can be so large, and from the outside point of view, the survival and development of organisms must have an external environment corresponding to it, so as to provide them with sufficient energy and material sources. After testing, the genes of this giant bacterium contain biochemical reaction genes that can be used for sulfur oxidation and carbon fixation, that is, some inorganic chemicals are taken from the surrounding environment and converted into energy through the physiological and chemical reactions of the body to meet the needs of metabolism, growth and development and reproduction.
From the analysis of scientists, this giant bacteria can not only fix carbon, use sugar, but also grow in various substrates and corresponding natural environments, in addition to each other's "communication", and even send signals, indicating that these giant bacteria not only have complex mechanisms beyond ordinary bacteria, but also have a certain "social behavior ability", which absolutely subverts our understanding of simple microbial characteristics.
Again, there are no wonders in the world, and in some corners of the world, there are definitely creatures and phenomena that we have never known before, waiting for us to discover and crack.
#美国科研团队发现2厘米长巨大细菌 #