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Bacteria: the story on HearLore | HearLore
Bacteria
Bacteria were the first life forms to appear on Earth, emerging approximately 4 billion years ago as the sole architects of the planet's early biosphere. For three billion years, these microscopic organisms dominated the planet, existing as the only life forms before the rise of more complex organisms. They are not merely present in the air, soil, and water, but thrive in the most hostile environments imaginable, from acidic hot springs to the deep biosphere of Earth's crust. These organisms constitute a domain of prokaryotic microorganisms that are typically a few micrometres in length, yet they possess a staggering capacity for survival. They are responsible for the putrefaction stage of decomposition, recycling nutrients and fixing nitrogen from the atmosphere to sustain the biological communities surrounding hydrothermal vents and cold seeps. Without these tiny entities, the nutrient cycle would collapse, and life as we know it would cease to exist. The sheer number of bacteria on Earth is estimated at 2 times 10 to the power of 30, forming a biomass that is only exceeded by plants, yet they remain largely invisible to the human eye.
The Hidden Majority
Despite the existence of an estimated 43,000 named species, the vast majority of bacteria have never been studied by science. A startling disparity exists in research focus, where just 10 bacterial species account for half of all publications, while nearly 75% of all named bacteria have no academic research devoted to them. The best-studied species, Escherichia coli, has more than 300,000 studies published on it, yet many of these papers use it merely as a cloning vehicle to study other species without providing insight into its own biology. A quarter of its 4,000 genes remain poorly studied or uncharacterized, highlighting a significant gap in our understanding. In contrast, some bacteria with minimal genomes, such as Mycoplasma, which have fewer than 600 genes, have a large fraction of their genes functionally characterized because most of them are essential and conserved. This imbalance means that 90% of scientific studies on bacteria focus on less than 1% of species, primarily those that are pathogenic and relevant to human health, leaving the silent majority of the microbial world largely unexplored.
The Shape of Survival
Bacteria display a wide diversity of shapes and sizes, ranging from spherical cocci to rod-shaped bacilli, and even spiral-shaped spirilla. While most bacterial cells are about one-tenth the size of eukaryotic cells, measuring between 0.5 and 5.0 micrometres in length, a few species are visible to the unaided eye. Thiomargarita namibiensis can reach half a millimetre long, and Epulopiscium fishelsoni reaches 0.7 millimetres, while Thiomargarita magnifica can grow up to 2 centimetres in length, which is 50 times larger than other known bacteria. These shapes are determined by the bacterial cell wall and cytoskeleton, influencing the ability to acquire nutrients, attach to surfaces, swim through liquids, and escape predators. Some bacteria, such as members of the genus Mycoplasma, measure only 0.3 micrometres, as small as the largest viruses. Beyond individual shapes, bacteria can associate in characteristic patterns, forming diploids, chains, or clusters like the bunch of grapes formed by staphylococci. In certain conditions, they can form larger multicellular structures, such as the elongated filaments of Actinomycetota species or the complex hyphae of Streptomyces species.
Bacteria emerged approximately 4 billion years ago as the first life forms to appear on Earth. They existed as the sole architects of the planet's early biosphere for three billion years before more complex organisms arose.
What is the largest known species of bacteria?
Thiomargarita magnifica can grow up to 2 centimetres in length, which is 50 times larger than other known bacteria. This species is visible to the unaided eye, unlike most bacteria that measure between 0.5 and 5.0 micrometres.
How many named species of bacteria exist?
There are an estimated 43,000 named species of bacteria, yet the vast majority have never been studied by science. Just 10 bacterial species account for half of all publications while nearly 75% of all named bacteria have no academic research devoted to them.
What are endospores and how do they help bacteria survive?
Endospores are highly resistant, dormant structures formed by certain genera of Gram-positive bacteria such as Bacillus and Clostridium. These structures contain a core of DNA and ribosomes protected by a multilayer rigid coat, allowing bacteria to survive extreme physical and chemical stresses including heat, freezing, radiation, and the vacuum of outer space.
Which bacteria are responsible for causing tetanus and anthrax?
Clostridium tetani endospores cause tetanus when they contaminate deep puncture wounds, while Bacillus anthracis endospores cause anthrax when inhaled. Both species belong to genera capable of forming highly resistant endospores that allow them to survive extreme conditions.
Some genera of Gram-positive bacteria, such as Bacillus, Clostridium, and Sporohalobacter, can form highly resistant, dormant structures called endospores. These endospores develop within the cytoplasm of the cell and contain a core of DNA and ribosomes surrounded by a cortex layer and protected by a multilayer rigid coat composed of peptidoglycan and a variety of proteins. Endospores show no detectable metabolism and can survive extreme physical and chemical stresses, including high levels of UV light, gamma radiation, detergents, disinfectants, heat, freezing, pressure, and desiccation. In this dormant state, these organisms may remain viable for millions of years. Endospores even allow bacteria to survive exposure to the vacuum and radiation of outer space, leading to the possibility that bacteria could be distributed throughout the universe by space dust, meteoroids, asteroids, comets, or planetoids. This resilience allows them to cause disease; for example, anthrax can be contracted by the inhalation of Bacillus anthracis endospores, and contamination of deep puncture wounds with Clostridium tetani endospores causes tetanus.
The Silent War
Pathogenic bacteria are a major cause of human death and disease, causing infections such as tetanus, typhoid fever, diphtheria, syphilis, cholera, foodborne illness, leprosy, and tuberculosis. Each species of pathogen has a characteristic spectrum of interactions with its human hosts. Some organisms, such as Staphylococcus or Streptococcus, can cause skin infections, pneumonia, meningitis, and sepsis, yet these organisms are also part of the normal human flora and usually exist on the skin or in the nose without causing any disease at all. Other organisms invariably cause disease in humans, such as Rickettsia, which are obligate intracellular parasites able to grow and reproduce only within the cells of other organisms. Some species, such as Pseudomonas aeruginosa, Burkholderia cenocepacia, and Mycobacterium avium, are opportunistic pathogens that cause disease mainly in people who are immunosuppressed or have cystic fibrosis. Bacterial infections may be treated with antibiotics, which are classified as bacteriocidal if they kill bacteria or bacteriostatic if they just prevent bacterial growth, but the overuse of antibiotics in farming and medicine is contributing to the rapid development of antibiotic resistance in bacterial populations.
The Ancient Discovery
Bacteria play a vital role in many stages of the nutrient cycle by recycling nutrients and the fixation of nitrogen from the atmosphere. They are responsible for the decomposition of dead bodies and the putrefaction stage in this process. In the biological communities surrounding hydrothermal vents and cold seeps, extremophile bacteria provide the nutrients needed to sustain life by converting dissolved compounds, such as hydrogen sulphide and methane, to energy. Bacteria are also used in the production of cheese and yogurt through fermentation, the recovery of gold, palladium, copper, and other metals in the mining sector, and in biotechnology. The ability of bacteria to degrade a variety of organic compounds is remarkable and has been used in waste processing and bioremediation. Bacteria capable of digesting the hydrocarbons in petroleum are often used to clean up oil spills, and fertiliser was added to some of the beaches in Prince William Sound in an attempt to promote the growth of these naturally occurring bacteria after the 1989 Exxon Valdez oil spill. In the chemical industry, bacteria are most important in the production of enantiomerically pure chemicals for use as pharmaceuticals or agrichemicals.
Like all animals, humans carry vast numbers of bacteria, approximately 10 to the power of 13 to 10 to
The Microbial Economy
the power of 14, with most being in the gut and many on the skin. Most of the bacteria in and on the body are harmless or rendered so by the protective effects of the immune system, and many are beneficial, particularly the ones in the gut. Nearly all animal life is dependent on bacteria for survival as only bacteria and some archaea possess the genes and enzymes necessary to synthesise vitamin B12, also known as cobalamin, and provide it through the food chain. The presence of over 1,000 bacterial species in the normal human gut flora of the intestines can contribute to gut immunity, synthesise vitamins such as folic acid, vitamin K, and biotin, and convert sugars to lactic acid. The presence of this gut flora also inhibits the growth of potentially pathogenic bacteria through competitive exclusion, and these beneficial bacteria are consequently sold as probiotic dietary supplements. Bacteria also live in mutualistic, commensal, and parasitic relationships with plants and animals, forming complex associations that are essential for their survival.