In fact, you don't have to avoid bacteria, because there are always many bacteria around you, which is unimaginable. Even if you are healthy and generally pay attention to hygiene, there are about one trillion bacteria eating on your skin-about 654.38+ million per square centimeter. There, they eat about 654.38 billion pieces of dander that you drop every day, plus delicious oil from every pore and tissue, and minerals that strengthen your body. You are the place where they hold a buffet dinner, and you also have the convenience of moving around. To show their gratitude, they give you a smell.
Just bacteria that live on your skin. There are trillions of bacteria entering your stomach and nostrils, sticking to your hair and eyelashes, swimming on the surface of your eyes and making holes in your gums. Your digestive system alone is the host of more than 100 trillion bacteria, with at least 400 species. Some break down sugar, some process starch, and some attack other bacteria. Many bacteria have no obvious effect, such as the ubiquitous intestinal spirochete. They just seem to like being with you. Each human body consists of about 65438+ billion cells, but it is the host of about 65438+ billion bacterial cells. In a word, bacteria are a big part of us. Of course, from the perspective of bacteria, we are only a small part of it.
We humans are big and smart, and can produce and use antibiotics and fungicides, so it is easy to think that we are going to exterminate bacteria. Don't believe that view. Bacteria may not build cities and lead interesting social lives, but they will still be here when the sun explodes. This is their planet, and we are here because they allow us to be here.
Don't forget, bacteria have lived without us for billions of years. Without them, we can't live a day. They treat our waste and make it useful; Nothing will rot without their hard chewing. They purify our water sources and make our soil fertile. They synthesize vitamins in our stomach, turn what we eat into useful sugars and polysaccharides, and fight against foreign bacteria that sneak into our stomach system.
We rely entirely on bacteria to collect nitrogen in the air and convert it into useful nucleotides and amino acids. This is an amazing and satisfying achievement. As margulies and Sagan pointed out, in order to do the same thing in industry (for example, when producing fertilizer), factories must heat raw materials to 500 degrees Celsius and extrude them to 300 times the normal atmospheric pressure. Bacteria have done it in no hurry. Thankfully, big creatures can't transport nitrogen without them. Most importantly, bacteria constantly provide us with breathing air and keep the atmosphere stable. Bacteria, including modern cyanobacteria, provide most of the oxygen for breathing on the earth. Algae and other microorganisms in the ocean spit out about 654.38+050 billion cubic kilometers of that gas every year.
In addition, bacteria are extremely fertile. Among them, energetic ones can produce a new generation in less than 10 minutes; Clostridium perfringens, a nasty little creature that causes gangrene, can reproduce within 9 minutes and then start dividing immediately. At this rate, theoretically, a bacterium can produce more offspring in two days than protons in the universe. According to Christian Dedif, a Belgian biochemist and Nobel Prize winner, "If given enough nutrition, a bacterial cell can produce 280 trillion individuals a day." At the same time, human cells can only divide once.
About every division of 6.5438+0.0000 times, a mutant will be produced. This is usually unfortunate for mutants-change is always dangerous for organisms-but occasionally, a new bacterium happens to have some advantages, such as the ability to get rid of or resist antibiotics. With this ability, another more terrible advantage will soon appear. Bacteria can enjoy information, and any bacteria can get several genetic codes from any other bacteria. As Margaret and Sagan said, all bacteria actually swim in the same gene pool. In the bacterial universe, the adaptive changes in one area will soon spread to any other area. It's like people can get the necessary genetic code from insects to grow wings or walk on the ceiling. From a genetic point of view, this means that bacteria have become a superorganism-small and scattered, but invincible.
No matter what you spit, drop or spill, bacteria can almost survive and reproduce on it. All you have to do is give them a little steam-for example, wipe the cupboard with a wet rag-and they will grow like nothing. They will corrode wood, glue in wallpaper and metal in dry paint. Australian scientists have found that a bacterium named Thiobacillus radiodurans lives in sulfuric acid with a concentration high enough to dissolve metals-in fact, they can't live without concentrated sulfuric acid. It has been found that a bacterium named Micrococcus radiodurans lives comfortably in the waste tank of nuclear reactor and feeds on plutonium and other residues. Some bacteria can decompose chemicals, but as far as we know, they can't get any benefits from them.
We also found that bacteria live in boiling mud and caustic soda pools, deep in rocks, on the seabed, in hidden ice pools in McMurdo Valley, Antarctica, and in the depth of the Pacific Ocean 1 1 km-where the pressure is more than 1000 times higher than the sea surface, which is equivalent to being pressed under 50 large passenger planes. Some bacteria seem really indestructible. According to The Economist, Micrococcus radiodurans is "almost unaffected by radiation". If you bombard its DNA with radiation, those fragments will recombine almost immediately, "just like the undead flying around in a horror movie."
Perhaps the most feasible one found so far is streptococcus. It stayed on the moon for two years, but it still came alive in the closed lens of the camera. In a word, there are few environments where bacteria can't live. Victoria Bennett said to me, "They found that when they put the probe into the hot underwater blowhole, even when the probe was about to melt, there were bacteria there."
In the 1920s, Edersen bustin and Frank Greer, two scientists from the University of Chicago, announced that they had isolated bacteria living in oil wells at a depth of 600 meters. This view is considered completely absurd-nothing can survive at a depth of 600 meters-for 50 years, people have always thought that their samples were contaminated by bacteria on the ground. We now know that there are a large number of microorganisms living in the depths of the earth, many of which have nothing to do with the ordinary organic world. They eat rocks, more precisely, things in rocks-iron, sulfur, manganese and so on. They also inhale strange things-iron, chromium, cobalt and even uranium. This process may have played a role in concentrating precious metals such as gold and copper, or in storing oil and natural gas. Some people even think that by chewing slowly and tirelessly, they also created bread crust.
Now some scientists believe that there are about 1000 billion tons of bacteria living under our feet. That place is called "the rock autotrophic microbial ecosystem under the surface"-the English abbreviation is SLiME. Thomas Gold of Cornell University estimated that if all the bacteria on the earth were taken out and piled on the surface of the earth, the earth could be buried at a depth of 15 meters-equivalent to the height of four floors. If this estimate is correct, there may be more life underground than on the surface.
Deep in the earth, microorganisms shrink and are extremely lazy. The most lively may be divided less than once a century, and some may be divided less than once in 500 years. As The Economist magazine said, "The key to a long life seems to be doing nothing." When the situation is quite bad, bacteria will shut down all systems and wait for a good year. 1997, scientists successfully activated some anthrax cells that had been dormant for 80 years in Trondheim Museum, Norway. There is a can of 1 18 canned meat and a bottle of 166 aged beer. As soon as they were opened, some microorganisms came to life immediately. 1996, scientists from the Russian Academy of Sciences claimed that they had revived the bacteria that had been frozen in the permafrost of Siberia for 3 million years. So far, the longest endurance record was announced in 2000 by Russell freeland of Westchester University in Pennsylvania and his colleagues, who claimed that they had revived bacteria 250 million years ago. This bacterium, named "Permian Bacillus", is trapped in a salt layer 600 meters underground in Carlsbad, New Mexico. If so, this microorganism is even older than the mainland.
It is understandable that this report is doubted by some people. Many biochemists believe that in such a long time, the composition of bacteria will degenerate and lose its function unless the bacteria wake up from time to time. However, even if bacteria do wake up from time to time, the energy in the body cannot last that long. More skeptical scientists believe that the sample may have been contaminated, if not in the process of collection, then it may have been contaminated when it was buried underground. 200 1 A team at Tel Aviv University in Israel believes that the Permian Bacillus is almost the same as modern bacteria. This bacterium, called Probacillus, was found in the Dead Sea. Only two genes differ in sequence, and the difference is very small.
"We should believe," Israeli researchers wrote, "that the genetic changes accumulated by Permian Bacillus in 250 million years can be completed in the laboratory in only 3-7 days?" Freeland's answer is: "Bacteria evolve faster in the laboratory than in the wild."
Maybe so.
Until the space age, most school textbooks still divided the biological world into two categories-plants and animals. This is incredible. Microorganisms are rarely placed in a prominent position. Amoebas and similar unicellular organisms are regarded as primitive animals, while algae are regarded as primitive plants. Bacteria are often mixed with plants, although everyone knows that bacteria are not plants. As early as the end of 19, ernst Heickell, a German naturalist, suggested that bacteria should belong to an independent world, which he called "prokaryotes". However, it was not until 1960s that this view was accepted by biologists, and only by some biologists. I noticed that this name is not recognized in the pocket American dictionary published by 1969. )
Traditional classification methods are not suitable for many microorganisms in the visible world. Fungi include mushrooms, molds, molds, yeasts and puffballs. Almost all of them are regarded as plants, but in fact, they have almost no characteristics-their reproduction mode, breathing mode and growth mode-consistent with the plant kingdom. In structure, they are more similar to animals because they build their own cells with chitin. That material makes its texture unique. Insect shells and mammalian claws are made of this material, although antlers and shovels are far less delicious than mushrooms. In particular, fungi do not produce photosynthesis like all plants, so they have no chlorophyll, so they are not green. Instead, they grew up eating directly. They eat almost everything. Fungi can corrode the sulfur on the concrete wall or the rotten material between your toes-neither plant can do it. They have almost only one plant feature, that is, they have roots.
This classification is even less applicable to a special kind of microorganisms, which used to be called myxobacteria, but now they are more often called myxobacteria. Their obscurity is undoubtedly related to this name. If the name sounds more energetic-for example, "mobile self-activated protoplasm"-and less like the kind of thing you will find when you go deep into the sewer, that unusual entity will almost certainly get the attention it deserves immediately, because Myxomycetes are undoubtedly the most interesting microorganisms in nature. In good times, they exist independently in the form of single cells, much like amoebas; When conditions get worse, they crawl and concentrate in a central position, almost miraculously becoming slugs. Slugs don't look beautiful and can't walk far-they usually just climb from the bottom of a pile of leaves to the top, in a relatively exposed position-but this may be the most wonderful trick in the universe for millions of years.
Things didn't end there. After climbing to the vantage point above, Myxobacteria transformed its face again, showing the shape of a plant. Through some wonderful and orderly process, those cells changed their shape, just like a small marching band, sticking out a stalk and forming a bud at the top, named "fruiting body" There are millions of spores in the fruiting body. At the right moment, those spores went away with the wind and became single-celled microorganisms, thus starting to repeat this process.
For many years, myxobacteria have been called protozoa by zoologists and fungi by mycologists, although most people can understand that they do not belong to any group. After the invention of gene detection method, the staff in the laboratory were surprised to find that Myxomycetes are so different and strange that they have nothing to do with anything else in nature, and sometimes they have nothing to do with each other.
1969, in order to sort out the increasingly inadequate classification, an ecologist named R. H. Weiteke of Cornell University put forward a proposal in the journal Science, which divided organisms into five main parts-the so-called "kingdom"-animal kingdom, plant kingdom, fungi kingdom, protozoan kingdom and Monera kingdom. Protozoa was originally proposed by Scottish biologist John Hogg to describe any living thing that is not a plant or an animal.
Although Weitek's new scheme is a great improvement, there is still no clear definition of protozoa. Some taxonomists keep this name to refer to large single-celled microorganisms-eukaryotic cells, but others use it as a drawer for storing single socks in biology, and stuff anything that doesn't fit anywhere, including (depending on what information you are looking for) myxomycetes, amoebas and even algae. According to some calculations, it always includes as many as 200,000 different creatures. That's a lot of socks.
Ironically, a down-to-earth scholar at the University of Illinois was about to complete a discovery just as Weitek's five-boundary classification began to be written into textbooks. This discovery will challenge everything. His name is Carl Voss, and he has been quietly studying the genetic continuity of bacteria since the 1960s-or as early as possible. In the early days, this was a very laborious process. It may take a year to study a bacterium at once. According to Voss, at that time, there were only about 500 known bacteria. This is less bacteria than your mouth. Today, this number is about 65,438+00 times that number, although it is far less than 26,900 species of algae, 70,000 species of fungi and 30,800 species of amoeba, and related microorganisms. Their stories are recorded in the annals of biology.
The total number of bacteria is so small, not entirely because people don't pay attention to it. Isolation and research of bacteria may be extremely difficult, and only about 1% can be propagated by culture. Considering their strong adaptability in the natural environment, there is one place where they seem unwilling to live, which is strange, and that is in Petri dishes. If you throw bacteria on agar medium, no matter how you caress them, most bacteria just lie there and refuse to reproduce. Any bacteria that reproduce in the laboratory can only be said to be an exception, and almost all of them are the objects of study by microbiologists. It's "like visiting a zoo and learning about animals," Voss said.
But because of the discovery of genes, Voss can study microorganisms from another angle. During the research, he realized that the microbial world can be divided into more basic parts. Many small creatures look like bacteria and behave like bacteria, but in fact they are completely different things-things that have been separated from bacteria for a long time. Voss called this microorganism primitive bacteria.
It must be said that distinguishing the characteristics of primitive bacteria from bacteria will only excite biologists. Most of these characteristics are reflected in the difference of lipids, and there is still a lack of something called peptidoglycan. In fact, it makes a world of difference. The difference between primitive bacteria and bacteria is greater than that between you and me and crabs or spiders. Voss discovered an unknown basic life species by himself. It is higher than the "boundary" level, and it is located at the top of the tree of life in the world, which is quite respectfully called.
1976, he redrawn the tree of life, including not five but 23 major "departments", which surprised the world-at least a few people paid attention to it. He divided these departments into three new main categories, which he called "fields"-bacteria, protobacteria and eukaryotic cells. The new arrangement is as follows: bacteria: cyanobacteria, purple bacteria, gram-positive bacteria, green non-sulfur bacteria, Flavobacterium, Huanghua and so on. Protobacteria: halophilic protobacteria, methanococcus, methanobacteria, methanococcus, Proteus, thermophilic bacteria, etc. Eukaryotic cells: microsporidia, trichomonas, flagellates, amoeba, myxobacteria, ciliates, plants, fungi and animals.
Voss' new classification has not caused a sensation in biology. Some people disdain his system and think it is too biased towards microorganisms. Many people completely ignore it. According to Francis Ashcraft, Voss was "extremely disappointed". However, his new scheme gradually began to be accepted by microbiologists. It will take longer for botanists and zoologists to see its advantages. The reason is not difficult to understand. According to Voss' model, both the plant kingdom and the animal kingdom are hung on the outermost branches of eukaryotic cells. In addition, others belong to single-celled organisms.
Voss 1966 said in an interview: "These people have always been classified according to the similarities and differences of their forms. "For many people, the idea of classifying by molecular order is not easy to accept." In short, they won't like it unless they see it with their own eyes. Therefore, they adhere to the common classification of five realms. For such an arrangement, Voss said "not very useful" when he was in a good mood, and more often said "completely led people astray." "Just like physics before," Voss wrote, "biology has developed to such a level that related objects and their interactions are often not seen by direct observation."
1998, Ernst Meyer, a great zoologist at Harvard University (he was 94 years old at that time; By the time I wrote this book, he was almost 100 years old and still very strong. He is even more afraid of chaos in the world, claiming that life can only be divided into two categories-his so-called "empire." Meyer said in a paper published in the Proceedings of the National Academy of Sciences that Voss' findings are interesting, but absolutely wrong, and pointed out that "Voss was not trained as a biologist and was not familiar with the classification principle, which is natural". When an outstanding scientist makes such comments on others, he is almost saying that that person has no idea what he is talking about.
The specific content of Meyer's comments is very technical-including what meiosis behavior, what branch of Henning evolution, and what controversial explanation is there for the genome of thermophilic alkaline methanobacteria-but fundamentally, he thinks that Voss's arrangement has made the tree of life out of balance. Meyer pointed out that the microbial community consists of only a few thousand species, while the original cell has only 175 named samples, and there may be thousands of undiscovered species-"but it will not exceed this number." There are millions of eukaryotic cells, that is, complex creatures with nuclear cells like us. In view of the "balance principle", Meyer advocates that simple microorganisms should be classified as prokaryotes, while other more complex and highly evolved organisms should be classified as eukaryotes, which are in the same position as prokaryotes. In other words, he advocated maintaining the previous classification as a whole. The difference between simple cells and complex cells lies in "a major breakthrough in biology."
If we have learned anything from Voss' new arrangement, it is that life is indeed diverse, and most of them are single-celled organisms that we are not familiar with. People can't help but think that evolution is a long process of continuous improvement, and it is a process of moving in a bigger and more complicated direction forever-in a word, in the direction of forming us. We are boasting ourselves. In the process of evolution, the actual difference has been very small in most cases. The appearance of a big guy like us is a complete fluke-an interesting little character. Of the 23 main life forms, only three-plants, animals and fungi-are big enough to be seen by the naked eye. Even among them, some species are extremely tiny. Voss believes that even if all the biomass of plants is added up-every living thing including plants, microorganisms should account for at least 80% of the total, maybe more. The world belongs to a very small creature-it has been for a long time.
So, at some point in life, you will inevitably ask, why do microbes hurt us so often? It makes us have a fever, or chills, or sores all over, or finally die. What good is it for microorganisms? After all, a dead host is unlikely to provide a long-term and suitable environment.
First of all, we should remember that most microorganisms are harmless or even beneficial to human health. The most infectious organism on earth, a bacterium called Wolbachia, would never harm humans or any other vertebrates-but if you were a shrimp, a worm or a fruit fly, you would wish you hadn't been born. According to National Geographic magazine, generally speaking, only one out of every 65,438+0,000 microorganisms is pathogenic to human beings-although we know that some of them will do bad things, so it is enough to think so. Even though most microbes are harmless, microbes are still the third biggest killer in the western world-although many don't kill us, they also make us deeply regret coming to this world.
Making the host uncomfortable is good for microorganisms. Symptoms are often conducive to the spread of bacteria. Vomiting, sneezing and diarrhea are good ways for bacteria to leave one host and prepare to live in another. The most effective way is to ask a mobile third party for help. Infectious microorganisms like mosquitoes, because their spines can send them directly into the flowing blood, can start working immediately before the victim's defense system finds out what attack they are under. Therefore, many Class A diseases-malaria, yellow fever, dengue fever, encephalitis and more than 65,438+000 other lesser-known but often serious diseases-begin with mosquito bites. Fortunately for us, the vector of AIDS-human immunodeficiency virus-is not among them, at least not yet. The human immunodeficiency virus inhaled by mosquitoes during biting is decomposed through their own metabolism. If one day the virus defeats this virus, we will really suffer.
However, from a logical point of view, it would be wrong to consider the problem too carefully, because microorganisms are obviously not very good at calculating entities. They don't care what they have done to you, just as you don't care about the pain caused by bathing with soap or killing millions of microorganisms with deodorant. When a pathogen kills you completely, it is also important to consider its own continued health. If they don't move to another host before destroying you, they will probably die by themselves. Jared diamond pointed out that there are many diseases in history that "once spread horribly everywhere, and then mysteriously disappeared, just as mysterious as when they appeared". He cited a severe but short-lived sweating fever, which was prevalent in Britain during the period of 1485- 1552, causing thousands of deaths and then burning the germs themselves. For any infectious bacteria, high efficiency is not a good thing.
A large number of diseases are not caused by microorganisms acting on you, but by your body trying to act on microorganisms. In order to eliminate pathogenic bacteria in the body, your immune system sometimes destroys cells or important tissues. So when you are unwell, what you feel is often not the pathogen, but the reaction produced by your own immune system. Being sick is a reasonable response to infection. The patient is lying in the hospital bed, thus reducing the threat to more people.
Because there are many things that may hurt you outside, there are a lot of white blood cells in your body-about100000 in total, and the duty of each kind is to identify and destroy a specific intruder. It is impossible and inefficient to maintain 6.5438+million different standing armies at the same time, so there are only a few sentinels left for each type of white blood cell in active service. Once an infectious agent-the so-called antigen-invades, the sentry concerned recognizes the invader and sends a request to his reinforcements. You may feel very uncomfortable when your body makes that kind of army. When the army finally went into battle, the rehabilitation work began.
White blood cells are merciless and will pursue every pathogen found until it is finally eliminated. In order to avoid the fate of destruction, the attacker has two basic strategies. They either attack quickly and then transfer to a new host, just like common infectious diseases such as colds; Or disguise yourself so that white blood cells can't identify themselves, just like the human immunodeficiency virus that causes AIDS. That virus can stay in the nucleus harmlessly for several years without being found, and then suddenly it starts to act.
Infection has many strange aspects. One of them is that some microbes that are completely harmless under normal circumstances sometimes enter the wrong parts of the human body-in the words of Brian Marsh, an infectious disease expert at Dartmouth Hitchcock Medical Center in Lebanon, New Hampshire-"a little crazy". "In a car accident, someone is internally injured, and this will always happen. Under normal circumstances, harmless microorganisms in the stomach will enter other parts of the body, such as flowing blood, causing serious harm. "
At present, the rarest and most uncontrollable disease caused by bacteria is fasciitis, which can lead to necrosis. Bacteria devour internal tissues, leaving a paste-like toxic residue, which actually eats the patient from the inside out. At first, patients are usually only slightly unwell, usually accompanied by rash and fever, but then their condition will deteriorate sharply. When you open it, you often find that the patient is being completely eaten. The only treatment is the so-called "radical resection"-that is, removing all the infected parts. 70% patients died, and many survivors were severely disfigured. Infectious pathogens are a common family of bacteria, called group A streptococci, which usually only cause streptococcal pharyngitis. In rare cases, due to unknown reasons, some of these bacteria will enter the throat wall and the human body itself, causing the most serious damage. They are completely resistant to antibiotics. This situation occurs about 1000 cases every year in the United States, and no one can say whether the situation will get worse.
The situation of meningitis is exactly the same. At least 10% of young people, maybe 30% of teenagers carry deadly meningococcus, but it is completely harmless for meningococcus to live in the throat. Very occasionally-about 65,438+0 out of 654.38 million young people-meningococcus will enter the blood and make them seriously ill. In the worst case, people can die within 12 hours. Extremely fast. "A person is fine at breakfast and dies at night." Marsh said.
If we hadn't abused the best weapon against bacteria like that: antibiotics, we would have won even greater victories. It is worth noting that according to one estimate, about 70% of antibiotics used in developed countries are often used in feed, just to promote growth or as a measure to prevent infection. Therefore, bacteria have every chance to develop drug resistance. They seized such an opportunity powerfully.
1952 penicillin is so effective against all kinds of staphylococci that William Stewart, director of the US Health Bureau, dared to say in the early 1960s, "It is time to end the era of infectious diseases. We have basically eliminated infectious diseases in the United States. " However, even when he said this, about 90% of these bacteria had developed resistance to penicillin. Not long after, a new kind of staphylococcus began to appear in the hospital, called methicillin-resistant staphylococcus. There is only one antibiotic: vancomycin, which is effective. However, in 1997, a hospital in Tokyo reported that a new staphylococcus strain had appeared and was resistant to this drug. Within a few months, staphylococcus spread to six other Japanese hospitals. Around the world, microbes began to win the war again: just in America.