symbiosis

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10 Terms

1
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endosymbiosis and ectosymbiosis

  • symbiont living either on the surface of the host or intracellularly

2
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metamonads

  • found in the gut of specific species of termites

  • lives in symbiosis with other bacteria: 2 endsymbiotic bacteria which degrades cellulose and replaces mitochondria and 3 ectosymbiotic bacteria which provide motility by possessing 4 non-functional flagella

3
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symbiotic associations in hemipteran insects

  • several bacterial species are found in insects which includes intracellular and extracellular bacteria. These are found in specialised structures called bacteriocytes can aggregate to form organs called bacteriomes

  • L.pneumophila is found in fresh water. Parasite of amoeba that can also replicate with alveolar macrophages

  • B.bacteriovorus attacks gram-negative bacteria. It invades the perupslams feed on host cell

<ul><li><p>several bacterial species are found in insects which includes intracellular and extracellular bacteria. These are found in specialised structures called bacteriocytes can aggregate to form organs called bacteriomes </p></li><li><p>L.pneumophila is found in fresh water. Parasite of amoeba that can also replicate with alveolar macrophages</p></li><li><p>B.bacteriovorus attacks gram-negative bacteria. It invades the perupslams feed on host cell</p></li></ul><p></p>
4
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plant nodulation as a model symbiosis

  • plants are unable to use atmospheric N2 and so some legumes can fix N2, via a symbiotic interaction with soil bacteria (rhizobia). The symbiotic process called nodulation is increasing growth and yield

5
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rhizobia

  • alphaproteobacterial (gram-negative)

  • soil dwelling bacteria is part of the rhizosphere

  • complex genome (5-10Mbp, several plasmids)

6
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nodulation process

  1. bacterial attraction: bacteria establishes contact with roots (production of roots exudates (flavonoids attract bacteria → activation of nodulation genes))

  2. production of nod factor (nod factors are short oligosaccharides)

  3. root curling

  4. formation of infection threads

  5. bacterial differentiation into bacteroids

  6. Nitrogen fixation

<ol><li><p>bacterial attraction: bacteria establishes contact with roots (production of roots exudates (flavonoids attract bacteria → activation of nodulation genes))</p></li><li><p>production of nod factor (nod factors are short oligosaccharides)</p></li><li><p>root curling</p></li><li><p>formation of infection threads</p></li><li><p>bacterial differentiation into bacteroids</p></li><li><p>Nitrogen fixation</p></li></ol><p></p>
7
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what distinguished obligate symbionts, parasites, organelles and viruses?

  • organelles are usually conserved across a wide range of organisms and are essential

  • parasites are harmful for the organism they infect

  • symbionts are often seen as beneficial organisms that live in association with other organisms

8
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new approaches allowed to define new species and shook the concept of minimal genome

  • most bacterrial species have been studied in axenic cultures (independently of any other living organism)

  • metagenomics allowed to identify thousands of bacterial species that cannot be grown in lab conditions

9
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what is the origin of small genomes in symbionts?

  • phylogenetic studies indicate that these organisms do not have an independent origin

  • genome size is the result of gene loss

<ul><li><p>phylogenetic studies indicate that these organisms do not have an independent origin </p></li><li><p>genome size is the result of gene loss</p></li></ul><p></p>
10
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a mosaic bionsynthetic pathway underpins…

  • amino acid biosynthesis