Microorganisms
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A microorganism ( from the Greek : μικρός , mikrós , " small " and ὀργ ανισμός, organismós , "organism"; also spelled microorganism or microbe is a microscopic organis m that comprises either a single cell (unicellular), cell clusters, or multicellular relatively complex organisms. The study of microorganisms is called microbiology , a subject that began with Anton van Leeuwenhoek 's discovery of microorganisms in 1675, using a microscope of his own design . Microorganisms are very diverse ; they include bacteria , fungi , algae , and protozoa ; microscopic plants ( green algae ); and animals such as rotifers and planarians . Some microbiologists also include viruses , but others consider these a re nonliving . Most microorganisms are unicellular ( single-celled ), but this is not universal , since some multicellular organisms are microscopic , while some unicellular protists and bacteria , like Thiomargarita namibiensis , are macroscopic and visible to the naked eye . Бичан О.И., ФГБВОУ ВО « Военно-медицинская академия имени С.М. Кирова» МО РФ
Microorganisms live in all parts of the biosphere where there is water , including soil , hot springs , the ocean floor . They can be found high in the atmosphere and deep inside rocks within the Earth's crust . Microorganisms are critical to nutrient recycling in ecosystems as they act as decomposers . As some microorganisms can fix nitrogen , they are a vital part of the nitrogen cycle , and recent studies indicate that airborne microbes may play a role in precipitation and weather . Microbes are also exploited by people in biotechnology , both in traditional food an d beverage preparation , and in modern technologies based on genetic engineering . However , pathogenic microbes are harmful , since they invade and grow within other organisms , causing diseases that kill humans , animals and plants .
Бичан О.И., ФГБВОУ ВО « Военно-медицинская академия имени С.М. Кирова» МО РФ
Evolution Single-celled microorganisms were the first form s of life to develop on Earth , approximately 3 billion –4 billion years ago . Further evolution was slow , and for about 3 billion years all organisms were microscopic . So , for most of the history of life on Earth the only forms of life were microorganisms . Bacteria , algae and fungi have been identified in amber that is 220 million years old , which shows that the morphology of microorganisms has changed little since the Triassic period Microorganisms tend to have a relatively rapid evolution . Most microorganisms can reproduce rapidly , and microbes such as bacteria can also freely exchange genes through conjugation , transformation and t ransduction . Бичан О.И., ФГБВОУ ВО « Военно-медицинская академия имени С.М. Кирова» МО РФ
Pre-microbiology The possibility that microorganisms exist was discussed for many centuries before their actual discovery in the 17th century . The existence of unseen microbiological life was postulated by Jainism , which is based on Mahavira's teachings as early as 6th century BC. Paul Dundas notes that Mahavira asserted existence of unseen microbiological creatures living in earth , water , air and fire . Jain scriptures also describe nigodas which are sub-microscopic creatures living in large clusters and having a very short life and are said to pervade each and every part of universe , even in tissues of plants and flesh of animals . However , the earliest idea to indicate the possibility of diseases spreading by yet unseen organisms was that of the Roman scholar Marcus Terentius Varro in a 1st century BC . In his book titled “ On Agriculture ” he says about harmfull particles near swamps : … and because there are certain minute creatures that cannot be seen by the eyes which float in the air and enter the body through the mouth and nose and there cause serious diseases . In The Canon of Medicine (1020), Abū Alī ibn Sīnā ( Avicenna ) hypothesized that tuberculosis and other diseases might be contag e ous In 1546, Girolamo Fracastoro proposed that epidemic diseases were caused by transferable seedlike entities that could transmit infection by direct or indirect contact or even without contact over long distances . All these early claims about the existence of microorganisms were speculative and were not based on any data or science . Microorganisms were neither proven , observed nor correctly and accurately described until the 17th century . The reason for this was the microscope . Бичан О.И., ФГБВОУ ВО « Военно-медицинская академия имени С.М. Кирова» МО РФ
History of microorganisms ' discovery Antonie van Leeuwenhoek , the first microbiologist and the first to observe microorganisms using a microscope . Antonie Van Leeuwenhoek (1632–1723) was one of the first people to observe microorganisms using a microscope of his own design and made one of the most important contributions to biology . Robert Hooke was the first to use a microscope to observe living things ; his book “ Micrographia ” published in 1665 contained descriptions of plant cells . Before Leeuwenhoek's discovery of microorganisms in 1675 it had been a mystery why grapes could be turned into wine , milk into cheese , or why food would spoil . Leeuwenhoek did not make the connection between these processes and microorganisms but using a microscope he did establish that there were forms of life that were not visible to the naked eye . Leeuwenhoek's discovery , along with subsequent observations by Spallanzani and Pasteur , ended the long-held belief that life spontaneously appeared from nonliving substances during the process of spoilage . Бичан О.И., ФГБВОУ ВО « Военно-медицинская академия имени С.М. Кирова» МО РФ
Lazzaro Spallanzani Lazzaro Spallanzani showed that boiling a broth stopped it from decaying Lazzaro Spallanzani (1729–1799) found that boiling broth would sterilise it and kill any microorganisms in it . He also found that new microorganisms could settle only in a broth if the broth was exposed to the air . Бичан О.И., ФГБВОУ ВО « Военно-медицинская академия имени С.М. Кирова» МО РФ
Louis Pasteur Louis Pasteur showed that Spallanzani's findings held even if air could enter through a filter that kept particles out Louis Pasteur (1822–1895) expanded upon Spallanzani's findings by exposing boiled broths to the air , in vessels that contained a filter to prevent all particles from passing through to the growth medium , and also in vessels with no filter at all , with air being admitted via a curved tube that would not allow dust particles to come in contact with the broth . By boiling the broth beforehand , Pasteur ensured that no microorganisms survived within the broths at the beginning of his experiment . Nothing grew in the broths in the course of Pasteur's experiment . This meant that the living organisms that grew in such broths came from outside , as spores on dust , rather than spontaneously generated within the broth . Thus , Pasteur dealt the death blow to the theory of spontaneous generation and supported germ theory . Бичан О.И., ФГБВОУ ВО « Военно-медицинская академия имени С.М. Кирова» МО РФ
Robert Koch Robert Koch showed that microorganisms caused disease . In 1876, Robert Koch (1843–1910) established that microbes can cause disease . He found that the blood of cattle who were infected with anthrax always had large numbers of Bacillus anthracis . Koch found that he could transmit anthrax from one animal to another by taking a small sample of blood from the infected animal and injecting it into a healthy one , and this caused the healthy animal to become sick . He also found that he could grow the bacteria in a nutrient broth , then inject it into a healthy animal , and cause illness . Based on these experiments , he devised criteria for establishing a causal link between a microbe and a disease and these are now known as Koch's postulates . Although these postulates cannot be applied in all cases , they do retain historical importance to the development of scientific thought and are still being used today . Бичан О.И., ФГБВОУ ВО « Военно-медицинская академия имени С.М. Кирова» МО РФ
Classification and structure Evolutionary tree showing the common ancestry of all three domains of life . Bacteria are colored blue , eukaryote red , and archaea green . Microorganisms can be found almost anywhere in the taxonomic organization of life on the planet . Bacteria and archaea are almost always microscopic , while a number of eukaryotes are also microscopic , including most protists , some fungi , as well as some animals and plants . Viruses are generally regarded as not living and therefore are not microbes , although the field of microbiology also encompasses the study of viruses . Бичан О.И., ФГБВОУ ВО « Военно-медицинская академия имени С.М. Кирова» МО РФ
Prokaryotes Prokaryotes are organisms that lack a cell nucleus and the other membrane bound organelles . They are almost always unicellular , although some species such as myxobacteria can aggregate into complex structures as part of their life cycle . Consisting of two domains , bacteria and archaea , the prokaryotes are the most diverse and abundant group of organisms on Earth and inhabit practically all environments where some liquid water is available and the temperature is below +140 °C. They are found in sea water , soil , air , animals ' gastrointestinal tracts , hot springs and even deep beneath the Earth's crust in rocks . Practically all surfaces that have not been specially sterilized are covered by prokaryotes . The number of prokaryotes on Earth is estimated to be around five million trillion trillion , or 5 × 10 30 , accounting for at least half the biomass on Earth . Бичан О.И., ФГБВОУ ВО « Военно-медицинская академия имени С.М. Кирова» МО РФ
Bacteria Almost all bacteria are invisible to the naked eye , with a few extremely rare exceptions , such as Thiomargarita namibiensis . They lack membrane-bound organelles , and can function and reproduce as individual cells , but often aggregate in multicellular colonies . Their genome is usually a single loop of DNA , although they can also harbor small pieces of DNA called plasmids . These plasmids can be transferred between cells through bacteria l conjugation . Bacteria are surrounded by a cell wall , which provides strength and rigidity to their cells . They reproduce by binary fission or sometimes by budding , but do not undergo sexual reproduction . Some species form extraordinarily resilient spores , but for bacteria this is a mechanism for survival , not reproduction . Under optimal conditions bacteria can grow extremely rapidly and can double as quickly as every 10 minutes Бичан О.И., ФГБВОУ ВПО « Военно-медицинская академия имени С.М. Кирова» МО РФ
Archaea Archaea are also single-celled organisms that lack nuclei . In the past , the differences between bacteria and archaea were not recognised and archaea were classified with bacteria as part of the kingdom Monera . However , in 1990 the microbiologist Carl Woese proposed the three-domain system that divided living things into bacteria , archaea and eukaryotes . Archaea differ from bacteria in both their genetics and biochemistry . For example , while bacterial cell membranes are made from phosphoglycerides with ester bonds , archaean membranes are made of ether lipids . Archaea were originally found in extreme environments , such as hot springs , but have since been found in all types of habitats . Only now scientists begin to realize how common archaea are in the environment , with crenarchaeota being the most common form of life in the ocean , dominating ecosystems below 150 m in depth . These organisms are also common in soil and play a vital role in ammoniaoxidation Бичан О.И., ФГБВОУ ВО « Военно-медицинская академия имени С.М. Кирова» МО РФ
Eukaryotes Most living things that are visible to the naked eye in their adult form are eukaryotes , including humans . However , a large number of eukaryotes are also microorganisms . Unlike bacteria and archaea , eukaryotes contain organelles such as the cell nucleus , the Golgi apparatus and mitochondria in their cells . The nucleus is an organelle that houses the DNA that makes up a cell's genome . DNA itself is arranged in complex chromosomes . Mitochondria are organelles which are the main saurce of the cell‘s energy containing the site s of the citric acid cycle and oxidativ e phosphorylation . They evolved from symbiotic bacteria and retain a remnant genome . Like bacteria , plant cells have cell walls , and contain organelles such as chloroplasts in addition to the organelles in other eukaryotes . Chloroplasts produce energy from light by photosynthesis , and were also originally symbiotic bacteria . Unicellular eukaryotes are those eukaryotic organisms that consist of a single cell throughout their life cycle . This qualification is significant since most multicellular eukaryotes consist of a single cell called a zygote at the beginning of their life cycles . Microbial eukaryotes can be either haploid or diploid , and some organisms have multiple cell nuclei coenocyte ). However , not all microorganisms are unicellular as some microscopic eukaryotes are made from multiple cells . Бичан О. И.,ФГБВОУ ВО «Военно-медицинская академия имени С.М. Кирова» МО РФ
Protists Of eukaryotic groups , the protists are most commonly unicellular and microscopic . This is a highly diverse group of organisms that are not easy to classify . Several algae species are multicellular protists , and slimе molds have unique life cycles that involve switching between unicellular , colonial , and multicellular forms . The number of species of protozoa is uncertain , since we may have identified only a small proportion of the diversity in this group of organisms . Бичан О.И., ФГБВОУ ВО « Военно-медицинская академия имени С.М. Кирова» МО РФ
Animals Most animals are multicellular , but some are too small to be seen by the naked eye . Microscopic arthropods include dust mites and spider mites . Microscopic crustaceans include copepods and the cladocera , while many nematodes are too small to be seen with the naked eye . Another particularly common group of microscopic animals are the rotifers , which are filter feeders that are usually found in fresh water . Micro-animals reproduce both sexually and asexually and may reach new habitats as eggs that survive harsh environments that would kill the adult animal . However , some simple animals , such as rotifers and nematodes , can dry out completely and remain dormant for long periods of time . Бичан О.И., ФГБВОУ ВО « Военно-медицинская академия имени С.М. Кирова» МО РФ
Fungi The fungi have several unicellular species , such as baker's yeast ( Saccharomyces cerevisiae ) and fission yeast ( Schizosaccharomyces pombe ). Some fungi , such as the pathogenic yeast Candida albicans can undergo phenotypic switching and grow as single cells in some environments and filamentous hyphae in others . Fungi reproduce both by budding or binary fission as well by producing spores which are called conidia or basidiospores . Бичан О.И., ФГБВОУ ВО « Военно-медицинская академия имени С.М. Кирова» МО РФ
Plants The green algae are a large group of photosynthetic eukaryotes that include many microscopic organisms . Although some green algae are classified as protists others such as charophyta are classified with embryophyte plants which are the most familiar group of land plants . Algae can grow as single cells or in long chains of cells . The green algae include unicellular and colonial flagellates usually but not always with two flagellaе per cell as well as various colonial , coccoid and filamentous forms . In the Charales which are the algae most closely related to higher plants cells differentiate into several distinct tissues within the organism . There are about 6000 species of green algae . Бичан О.И., ФГБВОУ ВО « Военно-медицинская академия имени С.М. Кирова» МО РФ
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