Bacteria - Biology

Bacteria - Biology

We are searching data for your request:

Forums and discussions:
Manuals and reference books:
Data from registers:
Wait the end of the search in all databases.
Upon completion, a link will appear to access the found materials.


What Are Bacteria?

Bacteria are microscopic, single-celled organisms that thrive in diverse environments. These organisms can live in soil, the ocean and inside the human gut.

Humans' relationship with bacteria is complex. Sometimes bacteria lend us a helping hand, such as by curdling milk into yogurt or helping with our digestion. In other cases, bacteria are destructive, causing diseases like pneumonia and methicillin-resistant Staphylococcus aureus (MRSA).

Different Types of Bacteria

Bacterial classification is more complex than the one based on basic factors like whether they are harmful or helpful to humans or the environment in which they exist. This article will give you a detailed classification of bacteria.

Bacterial classification is more complex than the one based on basic factors like whether they are harmful or helpful to humans or the environment in which they exist. This article will give you a detailed classification of bacteria.

What are bacteria?

Bacteria (singular: bacterium) are single-celled organisms which can only be seen through a microscope. They come in different shapes and sizes, and their sizes are measured in micrometer – which is a millionth part of a meter. There are several different types of bacteria, and they are found everywhere and in all types of environment.

Would you like to write for us? Well, we're looking for good writers who want to spread the word. Get in touch with us and we'll talk.

There are various groups of bacteria, which belong to the same family and have evolved from the same bacteria (ancestoral). However, each of these types possess their own peculiar characteristics – which have evolved after separation from the original species. The classification of bacteria is based on many factors like morphology, DNA sequencing, requirement of oxygen and carbon-dioxide, staining methods, presence of flagellae, cell structure, etc. This article will give you the classification of these micro-organisms based on all these factors, as well as a few other factors.

Classification of Bacteria

Before the invention of the DNA sequencing technique, bacteria were mainly classified based on their shapes – also known as morphology, biochemistry and staining – i.e. either Gram positive or Gram negative staining. Nowadays, along with the morphology, DNA sequencing is also used in order to classify bacteria. DNA sequencing helps in understanding the relationship between two types of bacteria i.e. if they are related to each other despite their different shapes. Along with the shape and DNA sequence, other things such as their metabolic activities, conditions required for their growth, biochemical reactions (i.e., biochemistry as mentioned above), antigenic properties etc. are also helpful in classifying the bacteria.

Based on Morphology, DNA Sequencing, and Biochemistry

Based on the morphology, DNA sequencing, conditions required and biochemistry, scientists have come up with the following classification with 28 different bacterial phyla:

  1. Acidobacteria
  2. Actinobacteria
  3. Aquificae
  4. Bacteroidetes
  5. Caldiserica
  6. Chlamydiae
  7. Chlorobi
  8. Chloroflexi
  9. Chrysiogenetes
  10. Cyanobacteria
  11. Deferribacteres
  12. Deinococcus-Thermus
  13. Dictyoglomi
  14. Elusimicrobia
  15. Fibrobacteres
  16. Firmicutes
  17. Fusobacteria
  18. Gemmatimonadetes
  19. Lentisphaerae
  20. Nitrospira
  21. Planctomycetes
  22. Proteobacteria
  23. Spirochaetes
  24. Synergistetes
  25. Tenericutes
  26. Thermodesulfobacteria
  27. Thermotogae
  28. Verrucomicrobia

Each phylum further corresponds to the number of species and genera of bacteria. In a broad sense, this bacterial classification includes bacteria which are found in various types of environment such as fresh-water bacteria, saline-water bacteria, bacteria that can survive extreme temperatures (as in sulfur-water-spring bacteria and bacteria found in Antarctica ice), bacteria that can survive in highly acidic environment, bacteria that can survive in highly alkaline environment, bacteria that can withstand high radiations, aerobic bacteria, anaerobic bacteria, autotrophic bacteria, heterotrophic bacteria, and so on…


Bacteria are tiny, one-celled organisms &ndash generally 4/100,000 of an inch wide (1 µm) and somewhat longer in length. What bacteria lack in size, they make up in numbers. A teaspoon of productive soil generally contains between 100 million and 1 billion bacteria. That is as much mass as two cows per acre.

A ton of microscopic bacteria may be active in each acre of soil.

Credit: Michael T. Holmes, Oregon State University, Corvallis. Please contact the Soil and Water Conservation Society at [email protected] for assistance with copyrighted (credited) images.

Bacteria dot the surface of strands of fungal hyphae.

Credit: R. Campbell. In R. Campbell. 1985. Plant Microbiology. Edward Arnold London. P. 149. Reprinted with the permission of Cambridge University Press. P lease contact the Soil and Water Conservation Society at [email protected] for assistance with copyrighted (credited) images.

Bacteria fall into four functional groups. Most are decomposers that consume simple carbon compounds, such as root exudates and fresh plant litter. By this process, bacteria convert energy in soil organic matter into forms useful to the rest of the organisms in the soil food web. A number of decomposers can break down pesticides and pollutants in soil. Decomposers are especially important in immobilizing, or retaining, nutrients in their cells, thus preventing the loss of nutrients, such as nitrogen, from the rooting zone.

A second group of bacteria are the mutualists that form partnerships with plants. The most well-known of these are the nitrogen-fixing bacteria. The third group of bacteria is the pathogens. Bacterial pathogens include Xymomonas and Erwinia species, and species of Agrobacterium that cause gall formation in plants. A fourth group, called lithotrophs or chemoautotrophs, obtains its energy from compounds of nitrogen, sulfur, iron or hydrogen instead of from carbon compounds. Some of these species are important to nitrogen cycling and degradation of pollutants.

What Do Bacteria Do?

Bacteria from all four groups perform important services related to water dynamics, nutrient cycling, and disease suppression. Some bacteria affect water movement by producing substances that help bind soil particles into small aggregates (those with diameters of 1/10,000-1/100 of an inch or 2-200µm). Stable aggregates improve water infiltration and the soil&rsquos water-holding ability. In a diverse bacterial community, many organisms will compete with disease-causing organisms in roots and on aboveground surfaces of plants.

A Few Important Bacteria

Nitrogen-fixing bacteria form symbiotic associations with the roots of legumes like clover and lupine, and trees such as alder and locust. Visible nodules are created where bacteria infect a growing root hair. The plant supplies simple carbon compounds to the bacteria, and the bacteria convert nitrogen (N2) from air into a form the plant host can use. When leaves or roots from the host plant decompose, soil nitrogen increases in the surrounding area.

Nitrifying bacteria change ammonium (NH4+) to nitrite (NO2-) then to nitrate (NO3-) &ndash a preferred form of nitrogen for grasses and most row crops. Nitrate is leached more easily from the soil, so some farmers use nitrification inhibitors to reduce the activity of one type of nitrifying bacteria. Nitrifying bacteria are suppressed in forest soils, so that most of the nitrogen remains as ammonium.

Denitrifying bacteria convert nitrate to nitrogen (N2) or nitrous oxide (N2O) gas. Denitrifiers are anaerobic, meaning they are active where oxygen is absent, such as in saturated soils or inside soil aggregates.

Actinomycetes are a large group of bacteria that grow as hyphae like fungi. They are responsible for the characteristically &ldquoearthy&rdquo smell of freshly turned, healthy soil. Actinomycetes decompose a wide array of substrates, but are especially important in degrading recalcitrant (hard-to-decompose) compounds, such as chitin and cellulose, and are active at high pH levels. Fungi are more important in degrading these compounds at low pH. A number of antibiotics are produced by actinomycetes such as Streptomyces.

Nodules formed where Rhizobium bacteria infected soybean roots.

Credit: Stephen Temple, New Mexico State University. P lease contact the Soil and Water Conservation Society at [email protected] for assistance with copyrighted (credited) images.

Actinomycetes, such as this Streptomyces, give soil its "earthy" smell.

Credit: No. 14 from Soil Microbiology and Biochemistry Slide Set. 1976. J.P. Martin, et al., eds. SSSA, Madison, WI. P lease contact the Soil and Water Conservation Society at [email protected] for assistance with copyrighted (credited) images.

Where Are Bacteria?

Various species of bacteria thrive on different food sources and in different microenvironments. In general, bacteria are more competitive when labile (easy-to-metabolize) substrates are present. This includes fresh, young plant residue and the compounds found near living roots. Bacteria are especially concentrated in the rhizosphere, the narrow region next to and in the root. There is evidence that plants produce certain types of root exudates to encourage the growth of protective bacteria.

Bacteria alter the soil environment to the extent that the soil environment will favor certain plant communities over others. Before plants can become established on fresh sediments, the bacterial community must establish first, starting with photosynthetic bacteria. These fix atmospheric nitrogen and carbon, produce organic matter, and immobilize enough nitrogen and other nutrients to initiate nitrogen cycling processes in the young soil. Then, early successional plant species can grow. As the plant community is established, different types of organic matter enter the soil and change the type of food available to bacteria. In turn, the altered bacterial community changes soil structure and the environment for plants. Some researchers think it may be possible to control the plant species in a place by managing the soil bacteria community.

Bug Biography: Bacteria That Promote Plant Growth

By Ann Kennedy, USDA Agricultural Research Service, Pullman, WA

Certain strains of the soil bacteria Pseudomonas fluorescens have anti-fungal activity that inhibits some plant pathogens. P. fluorescens and other Pseudomonas and Xanthomonas species can increase plant growth in several ways. They may produce a compound that inhibits the growth of pathogens or reduces invasion of the plant by a pathogen. They may also produce compounds (growth factors) that directly increase plant growth.

These plant growth-enhancing bacteria occur naturally in soils, but not always in high enough numbers to have a dramatic effect. In the future, farmers may be able to inoculate seeds with anti-fungal bacteria, such as P. fluorescens, to ensure that the bacteria reduce pathogens around the seed and root of the crop.

Bacteria - Biology

Bacteria are tiny little organisms that are everywhere around us. We can't see them without a microscope because they are so small, but they are in the air, on our skin, in our bodies, in the ground, and all throughout nature.

Bacteria are single-celled microorganisms. Their cell structure is unique in that they don't have a nucleus and most bacteria have cell walls similar to plant cells. They come in all sorts of shapes including rods, spirals, and spheres. Some bacteria can "swim" around using long tails called flagella. Others just hang out or glide along.

Are bacteria dangerous?

Most bacteria aren't dangerous, but some are and can make us sick. These bacteria are called pathogens. Pathogens can cause diseases in animals and plants. Some examples of pathogens are leprosy, food poisoning, pneumonia, tetanus, and typhoid fever.

Fortunately, we have antibiotics we can take which help to fight off the bad pathogens. We also have antiseptics to help us keep wounds clean of bacteria and antibiotic soap we use to wash to help keep off bad pathogens. Remember to wash your hands!

Not at all. Actually most bacteria are very helpful to us. They play an important role in the planet's ecosystem as well as in human survival.

Bacteria work hard in the soil for us. One type of bacteria, called decomposers, break down material from dead plants and animals. This might sound kind of gross, but it's an important function that helps to create soil and get rid of dead tissue. Another type of bacteria in the soil is Rhizobium bacteria. Rhizobium bacteria helps to fertilize the soil with nitrogen for plants to use when growing.

Yep, there's bacteria in our food. Yuck! Well, they aren't really that bad and bacteria is used when making foods like yogurt, cheese, pickles, and soy sauce.

Bacteria in our bodies

There are many good bacteria in our bodies. A primary use of bacteria is to help us digest and breakdown our food. Some bacteria can also help assist our immune system in protecting us from certain organisms that can make us sick.

Helpful and Harmful Types of Bacteria

Bacteria are microscopic organisms that form a huge invisible world around us, and within us. They are infamous for their harmful effects, whereas the benefits they provide are seldom known. Get a brief overview of the good and bad bacteria.

Bacteria are microscopic organisms that form a huge invisible world around us, and within us. They are infamous for their harmful effects, whereas the benefits they provide are seldom known. Get a brief overview of the good and bad bacteria.

For the first half of geological time our ancestors were bacteria. Most creatures still are bacteria, and each one of our trillions of cells is a colony of bacteria. – Richard Dawkins

Would you like to write for us? Well, we're looking for good writers who want to spread the word. Get in touch with us and we'll talk.

Bacteria – the oldest living organisms on earth – are omnipresent. The human body, the air we breathe, the surfaces we touch, the food we eat, the plants that surround us, the environment we live in, etc., are all replete with bacteria.

Almost 99% of these bacteria are helpful, where the remaining are notorious. In fact, some are essential for the proper growth of other living beings. They are either free-living or form a symbiotic relationship with animals or plants.

The list of helpful and harmful bacteria contain some of the most commonly known beneficial and deadly bacteria.

Characteristics: Gram-positive, rod-shaped

Presence: Lactobacilli species are present in milk and dairy products, fermented foods and also form part of our oral, intestinal and vaginal microflora. L. acidophilus, L. reuteri, L. plantarum, etc., are some of the most predominant species.

Benefit: Lactobacilli are known for their ability to utilize lactose and produce lactic acid, as a metabolic byproduct. This ability to ferment lactose makes lactobacilli an important ingredient for preparing fermented foods. It is also an important part of the pickling process since lactic acid serves as a preservative. The formation of yogurt from milk is done through what is called, fermentation. Certain strains are even used commercially for the production of yogurt. In mammals, lactobacilli aid the breakdown of lactose during digestion. The resulting acidic environment prevents the growth of other microbes in the body tissues. Being so, lactobacilli are an important part of probiotic formulations.

Characteristics: Gram-positive, branched, rod-shaped

Would you like to write for us? Well, we're looking for good writers who want to spread the word. Get in touch with us and we'll talk.

Presence: Bifidobacteria are present in the gastrointestinal tract of humans.

Benefit: Similar to lactobacilli these are also known for lactic acid production. In addition, it also produces acetic acid. This inhibits the growth of pathogenic bacteria by controlling pH levels in the intestines. B. longum helps in the breakdown of non-digestible plant polymers. B. longum and B. infantis help prevent diarrhea, candidiasis, and other yeast infections in infants and children. Owing to these benefits, this particular species are also included in commercially available probiotics.

Characteristics: Gram-negative, rod-shaped

Presence: E. coli is a part of the normal microflora of small and large intestines.

Benefit: E. coli helps in the breakdown of undigested monosaccharide sugars and thus aid digestion. These bacteria produce vitamin K and biotin which are essential for a variety of cellular processes.

Note.- Certain strains of E. coli can cause severe toxicity, diarrhea, anemia, and kidney failure.

Characteristics: Gram-positive, filamentous

Presence: They are widely found in soil, water, and decaying matter.

Benefit: Streptomyces spp. play an important role in soil ecology by bringing about the decomposition of organic matter present in soil. As a result, they are being explored as agents for bioremediation. S. aureofaciens, S. rimosus, S. griseus, S. erythraeus and S. venezuelae are some of the commercially important species used for the production of antibacterial and antifungal compounds.

Characteristics: Gram-negative, rod-shaped

Presence: Rhizobia are present in soil or form a symbiotic association with the root nodules of leguminous plants.

Benefit: Rhizobium etli, Bradyrhizobium spp., Azorhizobium spp.., and many other species, are useful for fixing atmospheric nitrogen, including ammonia, thus making it available for plants. Plants do not possess the ability to utilize atmospheric nitrogen and are dependent on nitrogen-fixing bacteria, that is present in soil.

Characteristics: Gram-negative, rod-shaped

Presence: Cyanobacteria are mainly aquatic bacteria but are also found on bare rocks and in soil.

Benefit: Also known as blue-green algae and blue-green bacteria, they are a group of environmentally significant bacteria. They bring about nitrogen fixation in aquatic habitats. Their calcification and decalcification abilities make them essential for maintaining coral reef ecosystem balance.

Characteristics: Neither Gram-positive or Gram-negative (due to high lipid content), rod-shaped

Presence: Mycobacteria are generally found in water and food. However, M. tuberculosis and M. leprae (aka, Hansen’s coccus spirilly), are obligate parasites and cannot survive in their free form.

Disease: The bacteria under the genus Mycobacterium are pathogens with long doubling times. M. tuberculosis and M. leprae, the most notorious species, are the causative agents for tuberculosis and leprosy, respectively. M. ulcerans causes ulcerated and non-ulcerated nodules in the skin. M. bovis causes tuberculosis in cattle.

Characteristics: Gram-positive, box-shaped

Presence: C. tetani spores are found in soil, skin, and the gastrointestinal tract.

Disease: C. tetani is the etiologic agent of tetanus. It enters the body through a wound, replicates there and releases toxins, namely tetanospasmin (aka, spasmogenic toxin) and tetanolysin. These lead to muscular spasms and respiratory failure.

Characteristics: Gram-negative, rod-shaped

Presence: Y. pestis can only survive within the host, namely rodents (fleas) and mammals.

Disease: Y. pestis causes bubonic and pneumonic plague. A skin infection with Y. pestis leads to the bubonic form characterized by malaise, fever, chills, and even seizures. An infection in the lungs caused by Y. pestis leads to pneumonic plague causing coughs, difficulty in breathing, and fever. According to WHO, around 1000 to 3000 cases of plague are reported worldwide every year. This microbe is being recognized and explored as a potential bioweapon.

Characteristics: Gram-negative, rod-shaped

Presence: H. pylori colonizes the mucosal lining of the human stomach.

Disease: It is the leading cause for gastritis and peptic ulcers. It produces cytotoxins and ammonia which damage the stomach epithelium leading to abdominal pain, nausea, vomiting, and bloating. H. pylori is present in half of the world’s population, however, most of them are asymptomatic while only a few develop gastritis and ulcers.

Characteristics: Gram-positive, rod-shaped

Presence: B. anthracis is widely present in soil.

Disease: The deadly disease called anthrax is a result of a B. anthracis infection, where the inhalation of B. anthracis endospores is what causes this illness. Anthrax mainly occurs in sheep, goats, cattle, etc. However, the transmission of bacteria from domestic cattle to humans, occurs in rare cases. The formation of sores, fever, headache, abdominal pain, nausea, diarrhea etc., are the most common symptoms (of anthrax).

We are surrounded by bacteria, some friendly and some deadly. It is up to us to make the most from these tiny living beings. Gain from the helpful ones by avoiding excessive or unnecessary use of antibiotics, and keep the harmful ones at bay by taking appropriate preventive measures, like maintaining hygiene and visiting the doctor from regular checkups.

Related Posts

Bacterial classification is more complex than the one based on basic factors like whether they are harmful or helpful to humans or the environment in which they exist. This article&hellip

Gram-negative bacteria refers to a broad category of bacteria that are unable to retain the crystal violet dye owing to their distinct cell wall structure. Know more about such bacteria&hellip

It is a preconceived notion that bacteria are always harmful to the human body. This is not true, as there exist bacteria that help in facilitating a healthy system in&hellip

Customers also viewed these products


"…the book is clearly written, broadly encompassing…" (Clinical Chemistry, December 2005)

"…this is a superb textbook and a valuable resource for all those interested, as either students or potential users of the science." (Journal of Natural Products, October 2005)

From the Inside Flap

The sixth edition has been extensively updated much of the text is new, or re-written, and there are many new references. Over 70 genera of bacteria, listed alphabetically, are described in the Appendix. Cross-references and a detailed index, maximise the accessibility of data.

Reviews of previous editions:

. a useful survey of the subject for students contemplating specialization.

Singleton assumes the reader has no prior knowledge of DNA and gene expression, and does an extraordinary job of explaining things from scratch.
--Quarterly Review of Biology

. recommended to undergraduates and those seeking clear explanations of basic concepts of bacteriology.
--Journal of Medical Microbiology

From the Back Cover

The sixth edition has been extensively updated much of the text is new, or re-written, and there are many new references. Over 70 genera of bacteria, listed alphabetically, are described in the Appendix. Cross-references and a detailed index, maximise the accessibility of data.

Reviews of previous editions:

"….a useful survey of the subject for students contemplating specialization."

"Singleton assumes the reader has no prior knowledge of DNA and gene expression, and does an extraordinary job of explaining things from scratch."
―Quarterly Review of Biology

"….recommended to undergraduates and those seeking clear explanations of basic concepts of bacteriology."
―Journal of Medical Microbiology

About the Author

Paul Singleton is an independent writer and editor in biomedical science. His works include DNA Methods in Clinical Microbiology Dictionary of Microbiology and Molecular Biology Bacteria in Biology, Biotechnology and Medicine and Antimicrobial Drug Action.

A microbe is any organism that is not visible with the naked eye. The unaided resolution of the eye is about 0.1mm

Bacteria are classified according to their shape:

1) Cocci: spherical bacteria

  • Cocci – smallest bacteria, occur as single spheres
  • Diplococci – pairs of spheres, e.g. pneumonia
  • Staphylococci – clusters of spheres, e.g. food poisoning
  • Streptococci – chains of spheres, e.g. sore throat

2) Bacilli: rod-shaped bacteria:

3) Spirilla – large, spiral-shaped bacteria - e.g. syphilis

4) Vibrio – crescent-shaped bacteria - e.g. cholera

Cell elongation results in the synthesis of additional cytoplasm & nuclear material

DNA replication takes place (there is no mitotic spindle), & the nuclear material attaches to the plasma membrane or mesosome

A septum begins to develop, & the nuclear material is distributed to both sides

The septum is completed, & a cell wall develops to divide the cell into two

The two daughter cells grow to a critical size, & then repeat this process

New genetic material can be inserted into a bacterium in three main ways:

1) Conjugation: bacteria link together by their pili.

  • Donor passes a plasmid called the F-factor (fertility) to the recipient cell.
  • The F-factor may be in a plasmid (replicating independently), or incorporated into the main bacterial chromosome

2) Transformation: one bacterium releases DNA which is absorbed by a second bacterium, allowing it to acquire new characteristics

3) Transduction: new genes can be inserted into the bacterial chromosome by a bacteria phage (a virus acting as a vector)

The bacterial population growth curve occurs in four main phases:

1) Lag phase: cells are active, but there is little increase in number.

2) Log phase: Nutrients & space are in plentiful supply, so there is little competition, & the bacteria multiply at their maximum rate

3) Stationary phase: carrying capacity (maximum number of bacteria that the environment can support) is reached, so intraspecific competition takes place between bacteria.

Hence the death rate balances the population growth rate, & the number of bacteria remains roughly constant

4) Death phase: nutrient supply is running out & waste products accumulate resulting in increased toxicity of environment.

Organisms are killed & population size eventually falls to zero.

Spores may be produced during stationary phase that are resistant to the adverse conditions

Bacterial growth can be controlled using physical methods (gamma irradiation or in an Autoclave using high temperatures) or by chemical means:

"Schrödinger's Bacterium" Could Be a Quantum Biology Milestone

The quantum world is a weird one. In theory and to some extent in practice its tenets demand that a particle can appear to be in two places at once&mdasha paradoxical phenomenon known as superposition&mdashand that two particles can become &ldquoentangled,&rdquo sharing information across arbitrarily large distances through some still-unknown mechanism.

Perhaps the most famous example of quantum weirdness is Schrödinger&rsquos cat, a thought experiment devised by Erwin Schrödinger in 1935. The Austrian physicist imagined how a cat placed in a box with a potentially lethal radioactive substance could, per the odd laws of quantum mechanics, exist in a superposition of being both dead and alive&mdashat least until the box is opened and its contents observed.

As far-out as that seems, the concept has been experimentally validated countless times on quantum scales. Scaled up to our seemingly simpler and certainly more intuitive macroscopic world, however, things change. No one has ever witnessed a star, a planet or a cat in superposition or a state of quantum entanglement. But ever since quantum theory&rsquos initial formulation in the early 20th century, scientists have wondered where exactly the microscopic and macroscopic worlds cross over. Just how big can the quantum realm be, and could it ever be big enough for its weirdest aspects to intimately, clearly influence living things? Across the past two decades the emergent field of quantum biology has sought answers for such questions, proposing and performing experiments on living organisms that could probe the limits of quantum theory.

Those experiments have already yielded tantalizing but inconclusive results. Earlier this year, for example, researchers showed the process of photosynthesis&mdashwhereby organisms make food using light&mdashmay involve some quantum effects. How birds navigate or how we smell also suggest quantum effects may take place in unusual ways within living things. But these only dip a toe into the quantum world. So far, no one has ever managed to coax an entire living organism&mdashnot even a single-celled bacterium&mdashinto displaying quantum effects such as entanglement or superposition.

So a new paper from a group at the University of Oxford is now raising some eyebrows for its claims of the successful entanglement of bacteria with photons&mdashparticles of light. Led by the quantum physicist Chiara Marletto and published in October in the Journal of Physics Communications, the study is an analysis of an experiment conducted in 2016 by David Coles from the University of Sheffield and his colleagues. In that experiment Coles and company sequestered several hundred photosynthetic green sulfur bacteria between two mirrors, progressively shrinking the gap between the mirrors down to a few hundred nanometers&mdashless than the width of a human hair. By bouncing white light between the mirrors, the researchers hoped to cause the photosynthetic molecules within the bacteria to couple&mdashor interact&mdashwith the cavity, essentially meaning the bacteria would continuously absorb, emit and reabsorb the bouncing photons. The experiment was successful up to six bacteria did appear to couple in this manner.

Marletto and her colleagues argue the bacteria did more than just couple with the cavity, though. In their analysis they demonstrate the energy signature produced in the experiment could be consistent with the bacteria&rsquos photosynthetic systems becoming entangled with the light inside the cavity. In essence, it appears certain photons were simultaneously hitting and missing photosynthetic molecules within the bacteria&mdasha hallmark of entanglement. &ldquoOur models show that this phenomenon being recorded is a signature of entanglement between light and certain degrees of freedom inside the bacteria,&rdquo she says.

According to study co-author Tristan Farrow, also of Oxford, this is the first time such an effect has been glimpsed in a living organism. &ldquoIt certainly is key to demonstrating that we are some way toward the idea of a &lsquoSchrödinger&rsquos bacterium,&rsquo if you will,&rdquo he says. And it hints at another potential instance of naturally emerging quantum biology: Green sulfur bacteria reside in the deep ocean where the scarcity of life-giving light might even spur quantum-mechanical evolutionary adaptations to boost photosynthesis.

There are many caveats to such controversial claims, however. First and foremost, the evidence for entanglement in this experiment is circumstantial, dependent on how one chooses to interpret the light trickling through and out of the cavity-confined bacteria. Marletto and her colleagues acknowledge a classical model free of quantum effects could also account for the experiment&rsquos results. But, of course, photons are not classical at all&mdashthey are quantum. And yet a more realistic &ldquosemiclassical&rdquo model using Newton&rsquos laws for the bacteria and quantum ones for photons fails to reproduce the actual outcome Coles and his colleagues observed in their laboratory. This hints that quantum effects were at play in both the light and the bacteria. &ldquoIt&rsquos a little bit indirect, but I think it&rsquos because they&rsquore only trying to be so rigorous in ruling out things and claiming anything too much,&rdquo says James Wootton, a quantum computing researcher at IBM Zurich Research Laboratory who was not involved in either paper.

The other caveat: the energies of the bacteria and the photon were measured collectively, not independently. This, according to Simon Gröblacher of Delft University of Technology in the Netherlands who was not part of this research, is somewhat of a limitation. &ldquoThere seems to be something quantum going on,&rdquo he says. &ldquoBut&hellipusually if we demonstrate entanglement, you have to measure the two systems independently&rdquo to confirm any quantum correlation between them is genuine.

Despite these uncertainties, for many experts, quantum biology&rsquos transition from theoretical dream to tangible reality is a question of when, not if. In isolation and collectively, molecules outside of biological systems have already exhibited quantum effects in decades&rsquo worth of laboratory experiments, so seeking out these effects for similar molecules inside a bacterium or even our own bodies would seem sensible enough. In humans and other large multicellular organisms, however, such molecular quantum effects should be averaged out to insignificance&mdashbut their meaningful manifestation within far smaller bacteria would not be too shocking. &ldquoI&rsquom a little torn about how surprising [this finding] is,&rdquo Gröblacher says. &ldquoBut it&rsquos obviously exciting if you can show this in a real biological system.&rdquo

Several research groups, including those led by Gröblacher and Farrow, are hoping to take these ideas even further. Gröblacher has designed an experiment that could place a tiny aquatic animal called a tardigrade in superposition&mdasha proposition much more difficult than entangling bacteria with light owing to a tardigrade&rsquos hundreds-fold&ndashlarger size. Farrow is looking at ways to improve on the bacterial experiment in 2019 he and his colleagues hope to entangle two bacteria together, rather than independently with light. &ldquoThe long-term goals are foundational and fundamental,&rdquo Farrow says. &ldquoThis is about understanding the nature of reality, and whether quantum effects have a utility in biological functions. At the root of things, everything is quantum,&rdquo he adds, with the big question being whether quantum effects play a role in how living things work.

It might be, for example, that &ldquonatural selection has come up with ways for living systems to naturally exploit quantum phenomena,&rdquo Marletto notes, such as the aforementioned example of bacteria photosynthesizing in the light-starved deep sea. But getting to the bottom of this requires starting small. The research has steadily been climbing toward macrolevel experiments, with one recent experiment successfully entangling millions of atoms. Proving the molecules that make up living things exhibit meaningful quantum effects&mdasheven if for trivial purposes&mdashwould be a key next step. By exploring this quantum&ndashclassical boundary, scientists could get closer to understanding what it would mean to be macroscopically quantum, if such an idea is true.

Jonathan O'Callaghan is a freelance space and science journalist based in London. You can follow him on Twitter @Astro_Jonny.

Biology - Bacteria

Bacteria normally comprises a large number of prokaryotic microorganisms.

Bacteria most probably were among the first life that formed to appear on the Earth.

Bacteria belong to Monera kingdom.

Bacteria usually inhabit in all range of environments, such as soil, water, acidic hot springs, radioactive waste, and the deep portions of Earth's crust.

The study of bacteria is known as bacteriology.

Bacteria play an important role in many stages of the nutrient cycle by recycling nutrients including the fixation of nitrogen from the atmosphere.

Bacteria grow to a fixed size and after maturity reproduce through asexual reproduction i.e. basically binary fission.

Under favorable conditions, bacteria can grow and divide very swiftly, and the bacterial populations can double merely in every 9.8 minutes.

When viruses that infect bacteria is known as Bacteriophages.

In order to modify themselves (to survive in the adverse environment), Bacteria frequently secrete chemicals into their environment.

Watch the video: Απλοειδή και Διπλοειδή Κύτταρα-Ομόλογα Χρωμοσώματα (October 2022).