A report on Microorganism

A cluster of Escherichia coli bacteria magnified 10,000 times
Antonie van Leeuwenhoek was the first to study microscopic organisms.
Lazzaro Spallanzani showed that boiling a broth stopped it from decaying.
Vardhmana Mahavira postulated the existence of microscopic creatures in the sixth century BC.
Louis Pasteur showed that Spallanzani's findings held even if air could enter through a filter that kept particles out.
Robert Koch showed that microorganisms caused disease.
Staphylococcus aureus bacteria magnified about 10,000x
Euglena mutabilis, a photosynthetic flagellate
A tetrad of Deinococcus radiodurans, a radioresistant extremophile bacterium
The photosynthetic cyanobacterium Hyella caespitosa (round shapes) with fungal hyphae (translucent threads) in the lichen Pyrenocollema halodytes
Wastewater treatment plants rely largely on microorganisms to oxidise organic matter.
A laboratory fermentation vessel
The eukaryotic parasite Plasmodium falciparum (spiky blue shapes), a causative agent of malaria, in human blood

Organism of microscopic size, which may exist in its single-celled form or as a colony of cells.

- Microorganism
A cluster of Escherichia coli bacteria magnified 10,000 times

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Bacteria

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Bacteria (singular bacterium, common noun bacteria) are ubiquitous, mostly free-living organisms often consisting of one biological cell.

Bacteria (singular bacterium, common noun bacteria) are ubiquitous, mostly free-living organisms often consisting of one biological cell.

Rod-shaped Bacillus subtilis
Phylogenetic tree of Bacteria, Archaea and Eucarya. The vertical line at bottom represents the last universal common ancestor.
Bacteria display many cell morphologies and arrangements
The range of sizes shown by prokaryotes (Bacteria), relative to those of other organisms and biomolecules.
Structure and contents of a typical Gram-positive bacterial cell (seen by the fact that only one cell membrane is present).
An electron micrograph of Halothiobacillus neapolitanus cells with carboxysomes inside, with arrows highlighting visible carboxysomes. Scale bars indicate 100 nm.
Helicobacter pylori electron micrograph, showing multiple flagella on the cell surface
Bacillus anthracis (stained purple) growing in cerebrospinal fluid
Many bacteria reproduce through binary fission, which is compared to mitosis and meiosis in this image.
A culture of ''Salmonella
A colony of Escherichia coli
Helium ion microscopy image showing T4 phage infecting E. coli. Some of the attached phage have contracted tails indicating that they have injected their DNA into the host. The bacterial cells are ~ 0.5 µm wide.
Transmission electron micrograph of Desulfovibrio vulgaris showing a single flagellum at one end of the cell. Scale bar is 0.5 micrometers long.
The different arrangements of bacterial flagella: A-Monotrichous; B-Lophotrichous; C-Amphitrichous; D-Peritrichous
Streptococcus mutans visualised with a Gram stain.
Phylogenetic tree showing the diversity of bacteria, compared to other organisms. Here bacteria are represented by three main supergroups: the CPR ultramicrobacterias, Terrabacteria and Gracilicutes according to recent genomic analyzes (2019).
Overview of bacterial infections and main species involved.
Colour-enhanced scanning electron micrograph showing Salmonella typhimurium (red) invading cultured human cells
In bacterial vaginosis, beneficial bacteria in the vagina (top) are displaced by pathogens (bottom). Gram stain.
Antonie van Leeuwenhoek, the first microbiologist and the first person to observe bacteria using a microscope.

They constitute a large domain of prokaryotic microorganisms.

Archaea

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Archaea (singular archaeon ) constitute a domain of single-celled organisms.

Archaea (singular archaeon ) constitute a domain of single-celled organisms.

Archaea were found in volcanic hot springs. Pictured here is Grand Prismatic Spring of Yellowstone National Park.
The ARMAN are a group of archaea recently discovered in acid mine drainage.
Membrane structures. Top, an archaeal phospholipid: 1, isoprene chains; 2, ether linkages; 3, L-glycerol moiety; 4, phosphate group. Middle, a bacterial or eukaryotic phospholipid: 5, fatty acid chains; 6, ester linkages; 7, D-glycerol moiety; 8, phosphate group. Bottom: 9, lipid bilayer of bacteria and eukaryotes; 10, lipid monolayer of some archaea.
Bacteriorhodopsin from Halobacterium salinarum. The retinol cofactor and residues involved in proton transfer are shown as ball-and-stick models.
Sulfolobus infected with the DNA virus STSV1. Bar is 1 micrometer.
Archaea that grow in the hot water of the Morning Glory Hot Spring in Yellowstone National Park produce a bright colour
Methanogenic archaea form a symbiosis with termites.

These microorganisms lack cell nuclei and are therefore prokaryotes.

Martinus Beijerinck in his laboratory in 1921

Virus

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Submicroscopic infectious agent that replicates only inside the living cells of an organism.

Submicroscopic infectious agent that replicates only inside the living cells of an organism.

Martinus Beijerinck in his laboratory in 1921
Antigenic shift, or reassortment, can result in novel and highly pathogenic strains of human flu
A typical virus replication cycle
Some bacteriophages inject their genomes into bacterial cells (not to scale)
The Baltimore Classification of viruses is based on the method of viral mRNA synthesis
Overview of the main types of viral infection and the most notable species involved
Transmission electron microscope image of a recreated 1918 influenza virus
Two rotaviruses: the one on the right is coated with antibodies that prevent its attachment to cells and infecting them.
The structure of the DNA base guanosine and the antiviral drug acyclovir
Peppers infected by mild mottle virus
Transmission electron micrograph of multiple bacteriophages attached to a bacterial cell wall
Scientist studying the H5N1 influenza virus

Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea.

A photomicrograph of a stool that has shigella dysentery. This bacteria typically causes foodborne illness.

Pathogen

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Any organism or agent that can produce disease.

Any organism or agent that can produce disease.

A photomicrograph of a stool that has shigella dysentery. This bacteria typically causes foodborne illness.
Magnified 100× and stained. This photomicrograph of the brain tissue shows the presence of the prominent spongiotic changes in the cortex, with the loss of neurons in a case of a variant of Creutzfeldt-Jakob disease (vCJD)
Two pinworms next to a ruler, measuring in 6 millimeters in length
Brown rot fungal disease on an apple. Brown rot typically target a variety of top-fruits.
A structure of Doxycycline a tetracycline-class antibiotic

Typically, the term pathogen is used to describe an infectious microorganism or agent, such as a virus, bacterium, protozoan, prion, viroid, or fungus.

Protist

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Any eukaryotic organism that is not an animal, plant, or fungus.

Any eukaryotic organism that is not an animal, plant, or fungus.

Phylogenetic and symbiogenetic tree of living organisms, showing the origins of eukaryotes
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In the five-kingdom system of Lynn Margulis, the term protist is reserved for microscopic organisms, while the more inclusive kingdom Protoctista (or protoctists) included certain large multicellular eukaryotes, such as kelp, red algae, and slime molds.

The bacterium Escherichia coli (E. coli), is a single-celled prokaryote

Organism

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Organism is any organic, living system that functions as an individual entity.

Organism is any organic, living system that functions as an individual entity.

The bacterium Escherichia coli (E. coli), is a single-celled prokaryote
An amoeba is a single-celled eukaryote
Polypore fungi and angiosperm trees are large multicellular eukaryotes.
Precambrian stromatolites in the Siyeh Formation, Glacier National Park. In 2002, a paper in the scientific journal Nature suggested that these 3.5 Gya (billion years old) geological formations contain fossilized cyanobacteria microbes. This suggests they are evidence of one of the earliest known life forms on Earth.
LUCA may have used the Wood–Ljungdahl or reductive acetyl–CoA pathway to fix carbon.

Organisms are classified by taxonomy into groups such as multicellular animals, plants, and fungi; or unicellular microorganisms such as protists, bacteria, and archaea.

Onion (Allium cepa) root cells in different phases of the cell cycle (drawn by E. B. Wilson, 1900)

Cell (biology)

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Basic structural and functional unit of life forms.

Basic structural and functional unit of life forms.

Onion (Allium cepa) root cells in different phases of the cell cycle (drawn by E. B. Wilson, 1900)
Structure of a typical prokaryotic cell
Structure of a typical animal cell
Structure of a typical plant cell
Detailed diagram of lipid bilayer of cell membrane
A fluorescent image of an endothelial cell. Nuclei are stained blue, mitochondria are stained red, and microfilaments are stained green.
Deoxyribonucleic acid (DNA)
Human cancer cells, specifically HeLa cells, with DNA stained blue. The central and rightmost cell are in interphase, so their DNA is diffuse and the entire nuclei are labelled. The cell on the left is going through mitosis and its chromosomes have condensed.
Diagram of the endomembrane system
Prokaryotes divide by binary fission, while eukaryotes divide by mitosis or meiosis.
An outline of the catabolism of proteins, carbohydrates and fats
An overview of protein synthesis.
Within the nucleus of the cell (light blue), genes (DNA, dark blue) are transcribed into RNA. This RNA is then subject to post-transcriptional modification and control, resulting in a mature mRNA (red) that is then transported out of the nucleus and into the cytoplasm (peach), where it undergoes translation into a protein. mRNA is translated by ribosomes (purple) that match the three-base codons of the mRNA to the three-base anti-codons of the appropriate tRNA. Newly synthesized proteins (black) are often further modified, such as by binding to an effector molecule (orange), to become fully active.
Staining of a Caenorhabditis elegans highlights the nuclei of its cells.
Stromatolites are left behind by cyanobacteria, also called blue-green algae. They are the oldest known fossils of life on Earth. This one-billion-year-old fossil is from Glacier National Park in the United States.
Robert Hooke's drawing of cells in cork, 1665

Most unicellular organisms are classed as microorganisms.

Grapes being trodden to extract the juice and made into wine in storage jars. Tomb of Nakht, 18th dynasty, Thebes, Ancient Egypt

Fermentation in food processing

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Grapes being trodden to extract the juice and made into wine in storage jars. Tomb of Nakht, 18th dynasty, Thebes, Ancient Egypt
Sourdough starter
Conical loaves of bread left as grave goods, exactly as laid out in the Great Tomb at Gebelein, Egypt, 2435-2305 BC.
Beer and bread, two major uses of fermentation in food
Nattō, a Japanese fermented soybean food
Batter made from rice and lentil (Vigna mungo) prepared and fermented for baking idlis and dosas
Fermenting cocoa beans
Cheeses in art: Still Life with Cheeses, Almonds and Pretzels, Clara Peeters, c. 1615
Chin som mok is a northern Thai speciality made with grilled, banana leaf-wrapped pork (both skin and meat) that has been fermented with glutinous rice

In food processing, fermentation is the conversion of carbohydrates to alcohol or organic acids using microorganisms—yeasts or bacteria—under anaerobic (oxygen-free) conditions.

Schematic representation of the nitrogen cycle. Abiotic nitrogen fixation has been omitted.

Nitrogen fixation

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Chemical process by which molecular nitrogen, with a strong triple covalent bond, in the air is converted into ammonia or related nitrogenous compounds, typically in soil or aquatic systems but also in industry.

Chemical process by which molecular nitrogen, with a strong triple covalent bond, in the air is converted into ammonia or related nitrogenous compounds, typically in soil or aquatic systems but also in industry.

Schematic representation of the nitrogen cycle. Abiotic nitrogen fixation has been omitted.
Nodules are visible on this broad bean root
A sectioned alder tree root nodule
Equipment for a study of nitrogen fixation by alpha rays (Fixed Nitrogen Research Laboratory, 1926)
Lightning heats the air around it breaking the bonds of starting the formation of nitrous acid.

Nitrogen fixation is carried out naturally in soil by microorganisms termed diazotrophs that include bacteria, such as Azotobacter, and archaea.

Clockwise from top left: Blepharisma japonicum, a ciliate; Giardia muris, a parasitic flagellate; Centropyxis aculeata, a testate (shelled) amoeba; Peridinium willei, a dinoflagellate; Chaos carolinense, a naked amoebozoan; Desmarella moniliformis, a choanoflagellate

Protozoa

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Clockwise from top left: Blepharisma japonicum, a ciliate; Giardia muris, a parasitic flagellate; Centropyxis aculeata, a testate (shelled) amoeba; Peridinium willei, a dinoflagellate; Chaos carolinense, a naked amoebozoan; Desmarella moniliformis, a choanoflagellate
Class Protozoa, order Infusoria, family Monades by Georg August Goldfuss, c. 1844
John Hogg's illustration of the Four Kingdoms of Nature, showing "Primigenal" as a greenish haze at the base of the Animals and Plants, 1860
The ciliate Spirostomum ambiguum can attain 3 mm in length
Isotricha intestinalis, a ciliate present in the rumen of sheep.
Paramecium bursaria, is one example of a variety of freshwater ciliates that host endosymbiont chlorophyte algae from the genus Chlorella
Resting cyst of ciliated protozoan Dileptus viridis.
Life cycle of parasitic protozoan, Toxoplasma gondii
Trophozoites of the amoebic dysentery pathogen Entamoeba histolytica with ingested human red blood cells (dark circles)

Protozoa (singular protozoon or protozoan, plural protozoa or protozoans) is an informal term for a group of single-celled eukaryotes, either free-living or parasitic, that feed on organic matter such as other microorganisms or organic tissues and debris.