The Social Microbe I Flashcards
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Pasteur and the germ theory
Sub surface origin hypothesis
Life originated at hydrothermal vents on ocean floors where the conditions were less hostile and more stable
What was the energy supply at hydrothermal vents?
Sub surface origin hypothesis
Supply of energy (reduced inorganic compounds - hydrogen and hydrogen sulphide)
What changed about Cyanobacteria’s metabolism that led to the great oxidation event?
Cyanobacteria used water instead of H2S to generate oxygen (oxygenic photosynthesis)
Why could the oxygen produced by Cyanobacteria not accumulate in the atmosphere?
It reacted spontaneously with reduced iron minerals to make iron oxides
How did the ozone layer appear?
Once all the iron was oxidised, oxygen could accumulate in the atmosphere
Define chemolithotroph
Organisms that obtain energy by oxidising inorganic compounds
Origin of eukaryotes (first event)
Endosymbiosis of a prokaryotic capable of aerobic respiration = led to mitochondria
Origin of eukaryotes (second event)
Endosymbiosis of cyanobacteria-like cell = led to photosynthesis
Who first noticed similarities between the bacteria and mitochondria ?
K. Mereschkovsky
1910
Evidence for endosymbiosis theory (8)
Mitochondria has its own DNA
Circular DNA
Double membrane suggests it was engulfed
Similar size to a bacteria
Mitochondria, bacteria and chloroplasts all have N-formal-methionine as the initiator amino acid
Antibiotic Rifampicin inhibits RNA polymerase action in bacteria and mitochondria but not in eukaryotic cells
Chloramphenicol inhibits protein synthesis in mitochondria, chloroplasts and prokaryotes but not in eukaryotes
Prokaryotes, mitochondria and chloroplasts all similarly have small ribosomes ranging from 60S - 75S.
Outer mitochondrial membrane
Protein-based pores which allow the passage of ions and molecules
Inner mitochondrial membrane
Loaded with proteins involved in electron transport and ATP synthesis
What is the initiator amino acid in mitochondria, chloroplasts and bacteria?
N-formyl-methionine
Define endocytosis
Cell Internalising material by invagination of its membrane to form a vesicle containing the material
Three types of endocytosis
- Phagocytosis
- Pinocytosis
- Receptor mediated endocytosis
Phagocytosis
Intake of solid material or food particles
Pinocytosis
Intake of mater dissolved in fluid
Receptor mediated endocytosis
Intake of molecules based on their interaction with receptors on cell surface
How are the stages of bacterial host adaption evidence for endosymbiosis theory
Self sufficient DNA, then it’s reduced because it loses genes it doesn’t need anymore once it’s in the host, eventually DNA becomes minimal.
= can see how mitochondrial DNA came to be (it’s an extreme stage obligate intracellular organelle)
Name an energy yielding organelle (alternative to a mitochondria)
Hydrogenosome
What are hydrogenosomes thought to have evolved from?
Mitochondria
How do hydrogenosomea generate energy?
Partial oxidation of pyruvate to acetate
Structure of hydrogenosomes
Double membrane
Contain own DNA
Circular
Define microaerophilic
(of a microorganism) requiring little free oxygen, or oxygen at a lower partial pressure
What are mitosomes?
Small organelles found in some anaerobic/microaerophilic organisms
What are mitosomes like
Reduced mitochondria lacking ETC and kerbs cycle proteins etc
Lack their own DNA
Name a rare eukaryote that doesn’t contain a mitochondria
Monocercomonoides
How did monocercomonoides evolve to not have a mitochondria?
Lateral gene transfer of sulfure genes so changed metabolism to bacterial sulfur mobilisation pathway do didn’t need mitochondria for energy
Eukaryotic cell as a genetic chimera
Contains:
Mitochondria from one bacterium
Chloroplasts from another bacterium
Prokaryotic symbiont will have passed some of its DNA to the host
Eukaryotic cells share some archaea molecular features of transcription and translation
Eukaryotic cells share ester linked membrane lipids and glycolysis pathway with bacteria
What is a diatom
Microscopic algae that has relationship with bacteria (proteobacteria and bacteriadetes)
Metabolic interactions between diatom and bacteria (3)
Parasitism (some bacteria secrete proteases that break down diatom membrane)
synergism (diatom get B12 from bacteria, diatom provides bacteria with dissolved organic matter)
Competition (in nutrient deficient environments)
Define synergism
Combined interaction producing effect greater than effect of separate things
Acanthomoeba
Free living amoeba that are important predators of microbial communities.
Contain obligate intracellulaire bacterial symbionts
Prokaryotic partnerships example
Tremblaya endosymbiosis
Secondary symbiosis
A living cell engulfs another eukaryotic cell (red or green alga) that has already undergone primary endosymbiosis
Secondary symbiosis example
Unrelated groups of nonphototrophic microbial eukaryotes acquired chloroplasts by engulfing eukaryotes already containing chloroplast
Primary endosymbiosis examples
Mitochondria, chloroplasts, hydrogenosomes being endocytosed
Serial endosymbiosis hypothesis
Eukaryotes already had a nucleus when they split from archaea. They then acquired mitochondria and chloroplasts by endosymbiosis.
Then there was LGT of genes from these endosymbiosis the the nuclear genome
Bacteria and eukarya have similar membrane lipids so this hypothesis doesn’t work. ( because if they have similar lipids then bacteria and eukarya should be more closely related but instead it’s eukarya branching from archaea)
Symbiogenesis (hydrogen) hypothesis
Symbiotic relationship between bacteria and archaea which resulted in the bacteria being engulfed to form a mitochondria
Hydrogen hypothesis = eukaryotic cell arose from bacteria and archaea association. Because hydrogen producing bacterial species associated with hydrogen consuming archaea species (metabolic syntrophy)
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Syntrophy
Interchangeable with symbiosis
Where is evidence of the metabolic syntrophy of bacteria and archaea found?
Methanogenic reactor
Syntrophy colonies of bacteria intertwined with filamentous archea (ones producing H2, other is consuming it)
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Mutualism
Symbiosis in which both species increase fitness
Commensalism
Symbiosis where one partner increases fitness without affecting the other species
Parasitism
Symbiosis where one species increases its fitness/benefits whist the other species’ fitness is adversely affected
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Define disease
Infection that damages the host
Define pathogenicity
Ability to cause disease
Define virulence
Severity of the disease caused
What is the mutualistic relationship of lichen between?
Fungi
Algae
Cyanobacteria
Role of fungi in lichen symbiosis
Absorbs water and minerals from environment
Role of algae or Cyanobacteria in lichen symbiosis
Use nutrients from photosynthesis and provide organic molecules
Mutualistic plant and bacteria example
Rhizobium and legumes
Role of bacterium in Rhizobium and plant symbiosis
Anaerobic nitrogen fixation in root nodule
Role of plant in Rhizobium and plant symbiosis
Provides nutrition and low oxygen environment in root nodule
4 stages of root nodule formation
- Rhizobia recognise and attach to root hair
- Rhizobia form infection thread and invade plant by travelling through it
- Bacteria change to bacteroids and packed root cells enlarge
- Enlarged root cells form a nodule
What genus of bacteria are common symbionts in earthworms?
Verminephrobacter
Worm bacteria X
- beneficial for host reproduction
- reductive evolution of bacterial genome thought to be due to streamlining, not genome degradation
Define streamlining
Theory that there is reproductive benefit to prokaryotes have a smaller genome size with less non coding DNA and fewer non essential genes
Explain why verminephrobacter genome isn’t completely reduced/degraded
Because their extracellular lifestyle (points in life outside the worm) gives them scope for genetic mixing with our strains etc
Whereas in obligate intracellular symbionts that live in genetically isolated and stable environments have much less, mostly no scope for genetic mixing
What genus do aphid symbionts belong to?
Buchnera
What genus do ant symbionts belong to?
Blochmania
What genus do tsetse fly symbionts belong to?
Wigglesworthia glossinidia brevipalpis
What are the three categories of insect symbionts
Obligate mutualists
Facultative symbionts
Reproductive manipulators
Define Obligate mutualists
Also called primary symbionts
Eg. Aphids have primary endosymbiosis in them
Species involved are in close proximity and can’t survive without one another
Define facultative symbionts
Also called secondary symbionts
Not required for host reproduction, invade various cell types or reproductive organs, can be introduced to previously uninflected hosts
Define reproductive manipulators
Parasites that spread by increasing host reproduction through their daughters at the expense of reproduction through their sons
What type of mutualists
are buchnera?
Explain
Obligate mutualists
Without buchnera, aphids die. (Bunchnera also can’t exist without aphids)
Explain the metabolic interdependence of aphids and buchnera?
Aphid: supplies energy, carbon, nitrogen
Buchnera: production of amino acids particularly tryptophan
Define bacteriocytes
Specialised cell, intracellularly located, in which the bacteria are inside
What are primary insect bacterial symbionts believed to be descended from (according to genome sequences)
Ancestral gamma proteobacterium (eg. E. Coli are an ancestor of buchnera - buchnera just has an incredibly reduced genome)
Example of facultative symbiont
Woolbachia
What is woolbachia in symbiosis with
Worm host (Brugia malayi)
What four distinct reproductive phenotypes can woolbachia cause?
- Feminisation
- Parthenogenesis
- Male killing
- Cytoplasmic incompatibility
Define feminisation (reproductive phenotype caused by woolbachia)
Results in genetic males that develop as females
Define Parthenogenesis (reproductive phenotype caused by woolbachia)
No male offspring produced if infected with woolbachia
Define male killing (reproductive phenotype caused by woolbachia)
Eliminates infected males whilst females survive
Define cytoplasmic incompatibility (reproductive phenotype caused by woolbachia)
Infected males cannot successfully mate with females unless they have the same woolbachia type
(Reproductive manipulator)
What’s a use of woolbachia?
Vector control of mosquitoes
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Bacteria are predisposed to particular relationships with their hosts
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What do termites digest and how
Lignocellulose (wood)
Done by symbiotic bacteria within them
Symbiosis in ruminants digestive system
Anaerobic bacteria in the rumen break down cellulose
Vibrio Fischeri
Hawaiian bobtail squid
Bacteria provide light
Squid provides amino acids and sugars but gets rid of bacteria in the day when it doesn’t need them
General things that bacteria and goats often provide each other
Bacteria provide metabolic capacity
Host provided precursors and homeostasis
