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BM108 🧬 > microbes and their enviroment > Flashcards

microbes and their enviroment Flashcards

1
Q

in a 70kg human how many bacteria are estimated to be inside them?

A

3.8 x10 to the power 13

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2
Q

what is symbiosis, mutualisation, commensalism and parasitisitism?

A

Symbiosis- close, long-term relationship between two organisms
Mutuilisation- both organisms benefit
Commensalusm- one benefits, the other is unaffected
Parasitism- one benefits, the other is harmed

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3
Q

what is ‘altruism’?

A

its community behaviour and the division of labour

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3
Q

what is ‘altruism’?

A

its community behaviour and the division of labour

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4
Q

bacteria need to sense the environment,

what do they need to sense in their environment?

A

what is in their enviroment

  • nutrients
  • amino acids
  • oxygen
  • pressure
  • surfaces
  • metals
  • essential ions
  • oxidative stress
  • light
  • toxic molecules
  • DNA damage
  • sugars etc.

other bacteria present

  • siblings
  • cousins
  • distant relatives

eukaryotic cells present

  • the host
  • what type

changes on gene expression (phenotype)

  • differentiation
  • virulence
  • metabolism
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5
Q

how do bacteria sense and respond to enviromental stimuli?

A
  • two component systems
    1. sensor kinase recognises the signal
    2. SK histidine is phosphorylated
    3. receptor transfers ~p to the response regulator
    4. response regulator activity (output)

however variations on this are often seen and there are also many other mechanisms for sensing and signalling

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5
Q

how do bacteria sense and respond to enviromental stimuli?

A
  • two component systems
    1. sensor kinase recognises the signal
    2. SK histidine is phosphorylated
    3. receptor transfers ~p to the response regulator
    4. response regulator activity (output)

however variations on this are often seen and there are also many other mechanisms for sensing and signalling

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6
Q

what is quorum sensing?

A

this is a way od sensing the presence and number of siblings, close kin and distant relatives

  • it works by small, specific molecules (autoinducers) accumulating as a function od cell density
  • these autoinducers are then sensed by receptor proteins, allowing the bacteria to determine when their cell density has reached a certain level (quorum) and coordinate expression of genes involved in group behaviours
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7
Q

what is the example from the notes which says about quorum sensing and bioluminescence?

A

the euprymna acolopes and vibrio fischeri
at high cell densities, the cells are producing bioluminescence and the squid are glowing as a result, this is regulated by quorum sensing
immature squid are colonised by free-living v. ficheri present in the environment.
bacteria colonise a specialised light otgan, establish an infection and divide using host supplied nutrients
the squid controls the amount of bacteria in the light organ
high cell density = high concentration of autoinducers
bacteria sense ‘quorum’ and turn on the genes for bioluminescence

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8
Q

what are the key regulators of bioluminecense and how do they work?

A
  • LuxR/ LuxI is an autoinducer synthases which produces specific AHL
  • N-3-oxohexanoyl-homoserine lactone (3-oxo-C6-HSL)
  • LuxR regulator binds AHL at high concentrations and directs the transcription of target genes (LuxCDBRG) > production of lucinferase and genes required for bioluminescence
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9
Q

what is staphococcus aureus?

A

its often sommensal present in the naval passages of humans

its an oppertunistic pathogen and can cause serious infections

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10
Q

what role does quorum sensing play in regards to staphococus aureus?

A

quorum sensing plays an important role In coordinating expression of virulence factors
it needs cells to express different proteins at different times during infection
at low cell densities, the concentration of the AI peptide is low: the cells express their adhesions
at high cell densities, the concentration of AI peptide is high and the cells express their toxins
this is believed to allow the bacteria to ‘stick’ during the initial phases of infection and once they gave established the infection, they express toxins which allow them to release more nutrients and move on to a new site

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11
Q

how does 2 RNA transcripts code for 4 proteins?

A

RNAIII is the output: transcriptional regulator is produced when quorum is reached

  • ArgA is the response regulator which directs the transcription of RNAIII
  • ArgB processes the signal peptide
  • ArgC is a histidine kinase which senses the AIP signal
  • ArgD is the unprocessed signal which then becomes AIP
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12
Q

what does the affect of ‘high cell densities having high concentrations of AI peptide’ and ‘low cell densities having low concentrations of AI peptide’ do?

A

this is beleived to allow the bacteria to ‘stick’ during the initial phases of infection and once they have established the infection they express toxins which allow them to release more nutrients and move to a new site

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13
Q

what does the arg system do?

A

it regualtes a number if different toxins and virulence factors
it also regulates other genes by specific base-pairing with their mRNA (it blocks or promotes translation)
- for example it activates the translation of hla gene
- alpha- toxin is a secreted toxin that forms pores in the host cell membrane > cell lysis

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14
Q

how can quorum sensing be complicated?

A

because different bacteria use diffrerent signalling molecules e.g. different AHLS
some bacteria use more than 1 system e.g. pseudomonas has 3 different circuits

15
Q

what is the chemical language of bacterial communication?

A

it uses different signlling molecules for diffrerent bacteria
gram-negative bacteria usually use AHLs
gram positive usually use short peptides
they also use ‘universal’ autoinducer AI-2 (and other QS signals)

16
Q

what are biofilms?

A

theyre microbial communities typically attached to a surface such as dental plaque or cathaters
they’re important for the pathogens of many bacteria
cells in biofilms are embedded in a matrix and are typically made up of polysaccharides, proteins and nucleic acids
‘monoxenic’ is when there is only 1 bacterial species, these are usually artificial and are often associated with infections
‘mixed’ means that there are several different microbial species and there may be more types of species than bacteria, they occur naturally and are environmentally important and are the main structure for bacterial populations in nature

17
Q

why make a biofilm?

A
  • biofilm structures help to trap and concentrate nutrients
    they also help to locate growth to favourable locations
    they help to prevent detachment in flowing systems
    they provide defence (against killing by immune cells and antibiotics)
    they allow community associations, division of labour (metabolic and genetic advantages)
18
Q

what stresses are biofilms resistant to?

A
  • antimicrobials cant penetrate into bioflims as the matrix acts as a physical barrier
  • cells in a biofilm grow and divide more slowly (antimicrobials target growth and division so would be less effective with bacterial cells in a biofilm)
  • expression of resistance genes
  • usually at least some cells survive the antibiotic treatment and so the biofilm can regrow
19
Q

what are the 5 stages of biofilm formation?

A
  1. attachment (requires motility and surface attachment)
  2. aggregation
  3. microcolony (further adaptation of life in a biofilm - production of matrix antibiotic resistance)
  4. detachment
20
Q

how is biofilm formation regulated?

A

its regulated by cell-cell communication (quorum sensing) and often by small molecule signals like cyclic di-GMP

21
Q

where are biofilms a huge problem?

A

theyre a huge problem clinically

  • diseases and bacteria forming biofilms on medical devices/ implants
  • bacteria resisting antibiotics
  • treatment/ causing recurrent infections
22
Q

what are the possible solutions to the clinical problems caused by biofilms?

A
  • physical disruption i.e. blasting them with ultrasound, but obviously not in a patient
  • prevent biofilm formation/ enhance derachment
  • develop drugs or drug therapies to disable the persisted phenotype
  • incorporate drugs into surfaces i.e. by inhibiting quorum sensing
23
Q

what is sporulation?

A

~20 genres of gram-positive bacteria can differentiate into endospores

  • sporulation is in response to stress conditions- desiccation, starvation and cell density
  • spores are metabolically dormant cells resistant to heat, toxins and radiation
  • they allow survival of adverse conditions and dispersal
  • they germinate when conditions are favourable
24
Q

what is endospre structure?

A

its a complex structure which contains dipicolinic acid and Ca2+(up to 10% of the dry weight
water is 10-30% down from normal levels
pH is down by ~1 unit
many small acid-soluble spore proteins (SASPs) produced, these tightly bind to DNA and protect it from damage, they also function as C and energy source during germination
about 200 genes are involved in endospore formation
there are complex signalling pathways between the mother cell and pre-spore component

25
Q

how are endospores stable?

A

theyre metabolically inactive and can survive without nutrients and water
they can survive temperature extremes, harsh chemical treatments and radiation
they can remain dormant for many years
they’re a bing problem in the canning of food as it makes the pathogens resistant to many anti-microbialtreatments

26
Q

what examples of bacteria are there that form endospores?

A

ones that cause disease: bacillus and colostridium species
ones that may be important for the pathogenisis of these bacteria: bactillus anthracis (anthrax), B. cereus (food poisoning), colostridium difficile (diarrhoea), C. botulinum (food poisoning)

27
Q

what does endospore stability germination mean?

A

endospores germinate to form a vegetative cell (which is capable of germinating again)

28
Q

what is needed for germination of endospores?

A
  • germinant receptors sense a favourable enviroment
  • endospore structures degraded, dipicolinic acid reached
  • outgrowth- swelling of core and expansion if cell, return ti normal metabolic energy

BM108 🧬 (17 decks)

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