Bacteria is a group of unicellular microorganisms. Typically several micrometers in length, bacteria have various shapes, some spherical, some spiral-shaped, some rod-shaped, some comma-shaped. Bacteria are present in every environment on earth. There are types that can grow in soil, sea water, ocean depths, earth crust, skin, intestines of animals, acidic hot water sources, radioactive wastes, cutting fluid emulsions. Typically, the number of bacterial cells in one gram of soil is 40 million, and in one milliliter of fresh water there is one million; Collectively, there are five nonillion (5×10³⁰) bacteria in the world, these make up most of the biomass of the earth. Bacteria are vital to the recycling of food and many important steps in food cycles depend on bacteria, such as nitrogen fixation from the atmosphere.
Bacteria vary greatly in shape and size, called morphology . Bacterial cells are about one-tenth the length of a eukaryotic cell, typically 0.5-5.0 micrometers in length. Most bacterial species are either spherical or rod-shaped. The spherical ones are koks (or coccus; from the Ancient Greek kókkos meaning seed ), the rod-like ones basil (Latin the bar is meaningfully named (from baculus ). Some rod-shaped bacteria, called vibrio, are somewhat curved or comma-shaped; others are spiral-shaped, called spirillum , or tightly coiled, called spirochete . A few species may be tetrahedron or cube-like. Some recently discovered bacteria grow in the form of long rods and have a star-shaped cross section. It has been suggested that the high area-to-volume ratio provided by this morphology gives these bacteria an advantage in low-nutrient environments. This great diversity in cell shapes is determined by the bacteria’s cell wall and cytoskeleton. Cell shape influences bacteria to obtain food, attach to surfaces, float in liquid, and escape from natural predators.
Most bacterial species survive as a single cell, while others are interconnected in their own unique ways: Neisseria forms diploids (binaries), Streptococcus chain, Staphylococcus Creates clusters like bunches of grapes. Some bacteria can elongate to form filaments, as in Actinobacteria. Filamentous bacteria often have a sheath with many cells in it. Some species, for example of the genus Nocardia , even form complex, branched filaments, similar to the mycelium in molds. Bacteria attach to surfaces and form dense clumps called biofilms. These films can range from a few micrometers thick to half a meter deep, and may contain multiple species of bacteria, Protista and archaea. Bacteria living in biofilms form a complex arrangement with cellular and extracellular components. Microcolonies can also be counted among the secondary structures that occur, and the duct networks in them provide easier diffusion of food. In natural environments, for example, on the surface of soil and plants, the majority of bacteria are attached to the surface via biophilia. Biofilms are also important in medicine because these structures are found in chronic bacterial infections and in medical devices implanted in the body. Bacteria that protect themselves in biofilms are much more difficult to destroy than bacteria that are isolated.
More complex morphological changes are also sometimes possible. For example, when deprived of amino acids, Myxobacteria use a process called quorum sensing to detect other cells in their vicinity.
In this process, bacteria move towards each other and form 500 micrometer-sized fruiting bodies containing about 100,000 bacteria. Bacteria found in seed structures perform different tasks; such cooperation constitutes a simple type of multicellular organization. For example, one out of every ten cells has this seed.
They migrate to the top of the m structures and form a specialized dormant (dormant) structure called myxospore . Myxospores are more resistant to drying and other adverse environmental conditions compared to normal cells
Carbon metabolism in bacteria is either heterotrophic, organic compounds are used as carbon source, or it is autotrophic, that is, carbon fixation of cellular carbon, carbon dioxide, is obtained. Typical autotrophic bacteria include phototrophic cyanobacteria, green sulfur bacteria, and some purple bacteria, but many chemolitrophic species are also included in this group, such as nitrogen-fixing and sulfur-oxidizing bacteria. The energy metabolism of bacteria is either phototrophy, that is, the use of light through photosynthesis, or chemotrophy, that is, the use of chemical compounds for energy, most of which are oxidized by oxygen or other alternative electron acceptors (aerobic or anaerobic respiration).
Finally, bacteria are classified as lithotrophs or organotrophs , respectively, according to their use of electron donors, either inorganic or organic compounds. Chemotrophic organisms use these electron donors for both energy conservation (by respiration or fermentation) and biosynthetic reactions, whereas phototrophic organisms use them for biosynthetic purposes only. Respiring organisms use chemical compounds as their energy source, in which electrons are transported from a reduced substrate to a final electron acceptor with an oxidation-reduction (redox) reaction.
With the energy released by this reaction, ATP is synthesized and metabolism is carried out. Oxygen is used as an electron acceptor in aerobic organisms. As a result of these, denitrification, sulfate reduction and acetogenesis processes, which are of great importance in ecology, occur.
In chemotrophs, in the absence of an electron acceptor, another possible life path is fermentation, in which electrons from reduced substrates are transferred to oxidized intermediates to produce products of fermentation, such as lactic acid, ethanol, hydrogen, butyric like acid Fermentation is possible because the energy level of the substrates is higher than that of the products, so that the organisms synthesize ATP and run their metabolism.
These processes are also important in biological responses to environmental pollution: for example, sulfate-reducing bacteria are largely responsible for the production of highly toxic forms of mercury (methyl- and dimethyl-mercury). Non-respiratory anaerobes produce energy and obtain reducing power through fermentation, while releasing metabolic by-products (such as ethanol in brewing) as waste. they do.
Lithotrophic bacteria use inorganic compounds as an energy source. Common electron donors are hydrogen, carbon monoxide, ammonia (which causes nitrification), ferrous iron and other reduced metal ions, and some reduced sulfur compounds. Methane gas is notable for its use by methanotrophic bacteria both as an electron source and as a substrate for carbon anabolism. In both aerobic phototrophy and chemolithotrophy, oxygen is used as the final electron acceptor, while inorganic compounds are used in anaerobic conditions. Most lithotrophic organisms are autotrophic, whereas organotrophic organisms are heterotrophic.
In addition to the fixation of carbon dioxide by photosynthesis, some bacteria fix nitrogen gas using the nitrogenase enzyme (nitrogen fixation). This environmentally important feature is seen in some bacteria in each of the metabolic types listed above, but is not universal.
Bacteria in the laboratory are often grown in solid or liquid media. Agar plate is used as solid growth medium, through which a pure culture of a bacterial strain is obtained. However, liquid growth media are used when it is necessary to measure the rate of growth or to obtain large volumes of cells.
Enzyme kinetics and gene expression data are used in mathematical models of living things to understand the biochemistry of the cell. This is possible in some well-studied bacteria, models of the Escherichia coli metabolism are being produced and tested. Thanks to the understanding of bacterial metabolism and genetics at this level, it is possible to redesign bacteria using biotechnology, thus enabling them to produce therapeutic proteins (such as insulin, growth factors or antibodies) more efficiently.
