Test Your Knowledge of Bacteria


Archaea, a primitive life form, were first found in extreme environments, with no oxygen, such as volcanic hot springs. The source of this bacteria is Grand Prismatic Spring of Yellowstone National Park.


Bacteria were among the first life forms to appear on Earth, and are present in all habitats on the planet. The nature of the original predecessor involved in the origin of life is subject to considerable speculation. It has been suggested that the original cell might have used RNA as its genetic material, since investigations have shown that RNA molecules can have numerous catalytic functions. Organisms must evolve or adapt to changing environments, and it is clear that mutations, which are changes in the sequence of nucleotides in an organism’s DNA, occur constantly in all organisms. You can find microbes everywhere and they are extremely adaptable to conditions, and survive wherever they are.


Most bacteria have not been characterized, and only about half of the phyla of bacteria have species that can be grown in the laboratory. The study of bacteria is known as 1) ___, a branch of microbiology. There are approximately ten times as many bacterial cells in the human flora as there are human cells in the body, with the largest number of the human flora being in the 2) ___ flora, and a large number on the skin. The vast majority of the bacteria in the body are rendered harmless by the protective effects of the immune system, and some are beneficial. However, several species of bacteria are pathogenic and cause infectious diseases, including cholera, syphilis, anthrax, leprosy, and bubonic plague. The most common fatal bacterial diseases are respiratory infections, with 3) ___ alone killing about 2 million people a year. In developed countries, antibiotics are used to treat bacterial infections and are also used in farming, making antibiotic resistance a growing problem.


Once regarded as plants constituting the class Schizomycetes, bacteria are now classified as prokaryotes. Unlike cells of animals and other eukaryotes, bacterial cells do not contain a nucleus and rarely harbor membrane-bound organelles. The ancestors of modern bacteria were unicellular microorganisms that were the first forms of life to appear on Earth, about 4 billion years ago, before there was 4) ___. For about 3 billion years, all organisms were microscopic, and bacteria and archaea were the dominant forms of life.


Complex morphological changes are sometimes possible. For example, when starved of amino acids, Myxobacteria detect surrounding cells in a process known as quorum sensing, migrate toward each other, and aggregate to form fruiting bodies up to 500 micrometres long and containing approximately 100,000 bacterial cells. In these fruiting bodies, the bacteria perform separate tasks; this type of cooperation is a simple type of multicellular organization. For example, about one in 10 cells migrate to the top of these fruiting bodies and differentiate into a specialized dormant state called myxospores, which are more resistant to drying and other adverse environmental conditions than are ordinary cells.


Many important biochemical reactions, such as energy generation, use concentration gradients across membranes. The general lack of internal membranes in bacteria means reactions such as electron transport occur across the cell 5) ___ between the cytoplasm and the periplasmic space. Some bacteria produce intracellular nutrient storage granules for later use, such as glycogen, polyphosphate, sulfur or polyhydroxyalkanoates. Certain bacterial species, such as the photosynthetic Cyanobacteria, produce internal gas vesicles, which they use to regulate their buoyancy – allowing them to move up or down into water layers with different light intensities and nutrient levels.




Structure and contents of a typical Gram positive bacterial cell


There are broadly speaking two different types of cell wall in bacteria, a thick one in the Gram-positives and a thinner one in the Gram-6) ___. The names originate from the reaction of cells to the Gram stain, a test long-employed for the classification of bacterial species.




Flagellum of Gram-negative Bacteria. The base drives the rotation of the hook and filament


The mechanisms inherent in bacteria are profound because they predict DNA evolutionary pathways of what is yet to come, first with more complex cells, which become more highly organized and ultimately more differentiated. One of the great mysteries of life was the beginning of bacterial organelle formation of the flagellum.


Although this short (bacteria) quiz can’t even begin to cover enough, we would be remiss to exclude a mention of the elegant flagellum of bacteria. Though no known multicellular organism is able to spin part of its body freely relative to another part of its 7) ___, there are two known examples of rotating molecular structures used by living cells. ATP synthase is an enzyme used in the process of energy storage and transfer, notably in photosynthesis and oxidative phosphorylation. It bears some similarity to the flagellar motors discussed below. The evolution of ATP synthase is thought to be an example of modular evolution, in which two subunits with their own functions have become associated and gained a new functionality. The only known example of a biological “wheel“ – a system capable of providing continuous propulsive torque about a fixed body – is the flagellum, a propeller-like tail used by single-celled prokaryotes for 8) ___. The bacterial flagellum is the best known example. About half of all known bacteria have at least one flagellum, indicating that rotation may in fact be the most common form of locomotion in living systems. At the base of the bacterial flagellum, where it enters the cell membrane, a motor protein acts as a rotary engine. The engine is powered by proton motive force, i.e., by the flow of protons (hydrogen ions) across the bacterial cell membrane due to a concentration gradient set up by the cell’s metabolism. (In species of the genus Vibrio, there are two kinds of flagella, lateral and polar, and some are driven by a sodium ion pump rather than a proton pump.) 9) ___ are quite efficient, allowing bacteria to move at speeds up to 60 cell lengths per second. The rotary motor at the base of the flagellum is similar in structure to that of ATP synthase. Spirillum bacteria have helically shaped bodies with flagella at either end, and spin about the central axis of their helical body as they move through the water.


Archaea, a group of prokaryotes distinct from bacteria, also feature flagella driven by rotary motor proteins, though they are structurally and evolutionarily distinct from bacterial flagella. Whereas bacterial flagella evolved from the bacterial Type III secretion system, archaeal flagella appear to have evolved from Type IV pili. The processes of evolution, as they are presently understood, can help explain why wheeled locomotion has not evolved in multicellular organisms; simply put, a complex structure or system will not evolve if its incomplete form provides no benefit to an organism. According to the modern evolutionary synthesis, adaptations are produced incrementally through natural selection, so major genetic changes will usually spread within populations only if they do not decrease the fitness of individuals. Although neutral changes that provide no benefit can spread through genetic drift, and detrimental changes can spread under some circumstances, large changes that require multiple steps will occur only if the intermediate stages increase fitness. The flagellum of bacteria, is the only known example of a freely rotating propulsive system in biology. In the 10) ___ of flagella, individual components were recruited from other structures, where they performed tasks unrelated to propulsion. The basal body that is now the rotary motor might have evolved from a structure used by the bacterium to inject toxins into other cells. This recruitment of previously evolved structures to serve new functions is called exaptation.


Bacteria, the first forms of life, are truly amazing and deserve our serious respect.


History of Bacteria Videos


Brief History of Bacteria – Part 1


Brief History of Bacteria – Part 2


Brief History of Bacteria – Part 3


Brief History of Bacteria – Part 4


ANSWERS: 1) bacteriology; 2) gut; 3) tuberculosis; 4) oxygen; 5) membrane; 6) negatives;7) body; 8)propulsion; 9) Flagella; 10) evolution



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