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Bacteria

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Bacteria
Temporal range:Archeanor earlier –present
Scanning electron micrographofEscherichia colirods
Scientific classificationEdit this classification
Domain: Bacteria
Woese,Kandler&Wheelis,1990
Phyla

Actinobacteria(high-G+C)
Firmicutes(low-G+C)
Tenericutes(nowall)

Aquificae
Bacteroidetes/Fibrobacteres–Chlorobi(FCB group)
Chlamydiae
Deinococcus-Thermus
Fusobacteria
Gemmatimonadetes
Nitrospirae
Planctomycetes–Verrucomicrobia/Chlamydiae(PVC group)
Proteobacteria
Spirochaetes
Synergistetes

  • Unknown/ungrouped

Acidobacteria
Chloroflexi
Chrysiogenetes
Cyanobacteria
Deferribacteres
Dictyoglomi
Thermodesulfobacteria
Thermotogae

Synonyms

EubacteriaWoese & Fox, 1977

Bacteria(singular:bacterium) are very smallorganisms.They areprokaryoticmicroorganisms.

Bacterialcellsdo not have anucleus,and most have noorganelleswith membranes around them. Most have acell wall.They do haveDNA,and theirbiochemistryis basically the same as other living things. They are amongst the simplest and the oldest organisms.

Almost all bacteria are so tiny they can only be seen through amicroscope.Bacteria are made up of onecell,so they are a kind ofunicellular organism.They were one of the earliest forms of life, and are simple single-celled organisms. They includeextremophiles,which live in extremehabitats.

There are probably more individual bacteria than any other sort of organism on the planet, exceptviruses.[1]Most bacteria live in thegroundor inwater,but many live inside or on the skin of other organisms, including humans. There are about as many bacterial cells as human cells in our bodies.[2][3]Some bacteria causediseases,but others help us in everyday activities like digesting food (gut flora). Some we use in factories to makecheeseandyogurt.

The founder ofbacteriologywas aGermanbiologistcalledFerdinand Cohn(1828–1898). He published the firstbiological classificationof bacteria, based on their appearance.[4]

Reproduction and gene transfer

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A bacteriumreproduces(creates more bacteria) bydividing in halfand creating two "daughter" cells. Each daughter is identical in shape to the parent.

Bacteria do not have sexes, but they do transmitDNAby several kinds ofhorizontal gene transfer.This is how they share resistance toantibioticsfrom one strain to another. The completeDNA sequenceis known for many bacterial strains. Each bacterium has only onechromosome.[5]

Shape

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Bacteria vary widely in size and shape, but in general they are at least ten times larger than viruses. A typical bacterium is about 1 µm (onemicrometer) in diameter, so a thousand bacteria lined up would be one millimeter long. There are about five nonillion (5×1030) bacteria on Earth.[1]

Bacteria are identified and grouped by their shapes. Bacilli are rod-shaped, cocci are ball-shaped, spirilla are spiral-shaped, and vibrio are shaped like a comma or a boomerang.

Different shapes of bacteria

Pathogens

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Pathogenicbacteria, the harmful kind, enter the human body from the air, water or food. Once inside, these bacteria attach themselves to or invade specific cells in our respiratory system, digestive tract or in any open wound. There they begin to reproduce and spread while using your body's food and nutrients to give them energy to help them reproduce.

Extremophiles

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Some bacteria areextremophiles.Somemicrobesthrive inside rocks up to 580 meters below the sea floor under 2.6 kilometers of ocean off thePacific Northwestof the United States.[6][7]According to one of the researchers, "You can find microbes everywhere — they're extremely adaptable to conditions, and survive wherever they are."[6]

Viruses

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Viruses were the first and are the most serious enemies of bacteria. Everywhere bacteria are, they get attacked by viruses. The viruses which attack bacteria are calledbacteriophages.

Something is now known about how bacteria protect themselves against viruses. Some bacteria and mostarchaeahaveCRISPR–Cas systems as anadaptivedefence against viruses. These keep sections of viralDNA.These are used to target and destroy later infections by the virus. The process is similar toRNA interference.[8][9]

History of their classification

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All modern ideas start with thesequence analysisof DNA and RNA. In 1987,Carl Woese,the forerunner of themolecular phylogenyrevolution, divided bacteria into 11 divisions based on 16Sribosomal RNA(SSU) sequences:[10][11]

  • Proteobacteria:Purple bacteriaand their relatives
    Alpha subdivision:purple non-sulfur bacteria, rhizobacteria,Agrobacterium,Bartonella,Rickettsiae,Nitrobacter)
    Beta subdivision:(Rhodocyclus,(some)Thiobacillus,Alcaligenes,Spirillum,Nitrosovibrio
    Gamma subdivision:enterics, fluorescent pseudomonads, purple sulfur bacteria,Legionella,(some)Beggiatoa
    Delta subdivision:Sulfur and sulfate reducers (Desulfovibrio),Myxobacteria,Bdellovibrio
  • Gram-positiveEubacteria
    High-G+C species -Actinobacteria(Actinomyces,Streptomyces,Arthrobacter,Micrococcus,Bifidobacterium)
    Low-G+C species -Firmicutes(Clostridium,Peptococcus,Bacillus,Mycoplasma)
    Photosynthetic species (Heliobacterium)
    Species with gram-negative walls (Megasphaera,Sporomusa)
    Cyanobacteriaand chloroplasts (Aphanocapsa,Oscillatoria,Nostoc,Synechococcus,Gleoebacter,Prochloron)
  • Spirochaetesand relatives
    Spirochetes (Spirochaeta,Treponema,Borrelia)
    Leptospiras (Leptospira,Leptonema)
  • Green sulfur bacteria(Chlorobium,Chloroherpeton)
  • Bacteroides,Flavobacteriaand relatives
    Bacteroides (Bacteroides,Fusobacterium)
    Flavobacterium group (Flavobacterium,Cytophaga,Saprospira,Flexibacter)
  • Planctomycesand relatives
    Planctomyces group (Planctomyces,Pasteuria)
    Thermophiles (Isocystis pallida)
  • Chlamydiae(Chlamydia psittaci,Chlamydia trachomatis)
  • Radioresistant micrococciand relatives
    Deinococcus group (Deinococcus radiodurans)
    Thermophiles (Thermus aquaticus)
  • Green non-sulfur bacteriaand relatives
    Chloroflexus group (Chloroflexus,Herpetosiphon)
    Thermomicrobium group (Thermomicrobium roseum)
  • Thermotogae
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TheSimple English Wiktionaryhas adefinitionfor: bacteria.

References

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  1. ↑1.01.1Whitman W, Coleman D, Wiebe W (1998)."Prokaryotes: the unseen majority".Proc Natl Acad Sci USA.95(12): 6578–83.Bibcode:1998PNAS...95.6578W.doi:10.1073/pnas.95.12.6578.ISSN0027-8424.PMC33863.PMID9618454.{{cite journal}}:CS1 maint: multiple names: authors list (link)
  2. ↑Crew, Bec (11 April 2018)."Here's how many cells in your body aren't actually human".ScienceAlert.Retrieved2019-08-07.
  3. ↑Yong, Ed (2016-01-08)."You're probably not mostly microbes".The Atlantic.Retrieved2019-08-07.
  4. ↑Encyclopedia Britanniaca: Bacteriology
  5. ↑"Bacterial DNA – the role of plasmids".
  6. ↑6.06.1Choi, Charles Q. (2013)."Microbes thrive in deepest spot on Earth".LiveScience.Retrieved17 March2013.
  7. ↑Oskin, Becky (2013)."Intraterrestrials: Life thrives in ocean floor".LiveScience.Retrieved17 March2013.
  8. ↑van der Oost J, Westra ER, Jackson RN, Wiedenheft B (July 2014)."Unravelling the structural and mechanistic basis of CRISPR-Cas systems".Nature Reviews. Microbiology.12(7): 479–92.doi:10.1038/nrmicro3279.PMC4225775.PMID24909109.
  9. ↑Hille F, Richter H, Wong SP, Bratovič M, Ressel S, Charpentier E (March 2018). "The biology of CRISPR-Cas: backward and forward".Cell.172(6): 1239–1259.doi:10.1016/j.cell.2017.11.032.hdl:21.11116/0000-0003-FC0D-4.PMID29522745.S2CID3777503.
  10. ↑Woese C.R. 1987. Bacterial evolution.Microbiological reviews51(2): 221–71.[1]
  11. ↑Holland L. (1990). "Woese, Carl in the forefront of bacterial evolution revolution".Scientist.3(10).
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