Control of Prokaryotic Growth Flashcards
Most bacterial cells divide via
binary fission
Describe binary fission
- cell elongation
- central septum formation
- cell wall formation occurs intercalatorially
- cells separate
Describe the products of binary fission
one bacterial cell has equal products under binary fission: 2 genetically identical daughter clones
Describe budding
- simple budding
- budding from hyphae
- unequal products in division
- cell wall formation is not intercalatory, but polar
Give examples of cells exhibiting simple budding
- Pirellula
- Blastobacter
Give examples of cells exhibiting budding from hyphae
- Hyphomicrobium
- Rhodomicrobium
- Pedomicrobedium
Describe Caulobacter formation
- relies on unequal products post-division
- stalks produce differentiated swimmer cells while the stalk itself holds fast
What is Caulobacter
a stalked organism
Give an example of unequal products formation
- when a cell undergoes polar growth without differentiation of cell size (without elongating first)
- occurs in the Rhodopseudomonas, the Nitrobacter and the Methylosinus
What is the adaptation of efficient cell division in bacteria?
exponential growth
One bacterial cell can divide into … after 10 hours
1,048,576
How is bacterial growth rate calculated?
- measure logarithmic cell abundance per ml against time
- plotting this graphically to allow slope calculation (the rate of division)
- can also calculate g
What is g, in terms of bacterial cell division?
the mean generation time (time taken for cell abundance to double)
Why does bacterial culture growth occur in stages?
Because exponential growth is not sustainable in vitro
Describe the experimental set up for investigating bacterial culture growth
- culture inside of a culture vessel with room for a gaseous headspace
- overflow collected
- effluent microbial cells analysed
Describe the classification of stages of bacterial cell culture growth
- lag
- exponential
- stationary
- death phases
Describe the lag phase
- post-incodulation
- due to the change of growth conditions in minerals and nutrients
Describe the exponential phase
- relatively short
- where g is calculated
Describe exponential growth
- requires very rich media
- not always feasible
Describe the death phase
- often protracted
- can be replaced by a quiescent phase if resistance is horizontally acquired
How is bacterial abundance calculated?
- the viable organism count
- turbidity (via optical density)
Explain the inability of expontential growth to persist
- nutrients are limiting
Describe bacterial culture growth on sugar
- usually produce an acid
- toxifies the product, limiting growth by mutation induction
Describe bacterial culture growth on organic acid
tends to alkalise the media, resulting in slowed or arrested growth
How to set up experimentally to maximise the likelihood of prolonged exponential growth
- allow for fresh medium from a resevoir via a flow-rate regulatory mechanism
- sterile air or other necessary metabolic gases
When measuring g
dilution rate is directly proportional to growth rate
Describe the minimum for bacterial temperature
- undergo membrane gelling
- transport processes are so slow as to not facilitate growth
Describe bacteria at their optimum temperature
metabolism is at the maximum possible rate
Describe the maximum for bacterial temperature
- protein denaturation occurs
- cytoplasmic membrane collapse
- thermal lysis
Psychrophile Polaromonas vascuolata
optimum is 4 degrees Celsius
Mesophile Escherichia Coli
optimum is 39 degrees Celsius
Thermophile Geobacillus stearothermophilus
optimum is 60 degrees Celsius
Hyperthermophilic archaea Pyrolobus fumerii
optimum is 106 degrees Celsius
Describe Alkaliphiles
- prefer alkaline pHs (of greater than or equal to 8
- Chloroflexus aurantiacus
- Bacillus firmus
- archaea: Natronobacterium gregoryi
Describe Acidophiles
- prefer acidic pHs (lesser than 5.5)
- Rhodopila globiformis
- Acidithiobacillus ferrooxidans
- archaea: Picrophilus oshimae
Describe Neutrophiles
- prefer central pHs (greater than 5.5, but lesser than 8)
- E. Coli
Describe the acidic environments in which bacteria might dwell
- volcanic soils and waters
- gastric fluids
- citric fruits
- mine drainage efflux
Alkaline examples are found in
- seawater
- some lakes
- limey environments
Why are buffers necessary?
to ensure the efficient and adequate growth of media cultures
What is osmolarity?
an organism’s sensitivity to sodium chloride
Describe Nonhalophiles
- those who do not tolerate any salt
- E. Coli
Describe Halotolerance
- grow at lesser than 5 percentage NaCl - Staphylococcus aureus.
Describe Halophiles
- grow between 5 and 10 percent NaCl
- Aliivibrio fischeri
Describe Extreme halophiles
- grow at greater than 15% NaCl
- Halobacterium salinarum.
Describe the different categories of aerobicity
- obligate
- facultative
- microaerophilic
Describe obligate aerobes
- oxygen is required to complete aerobic respiration
- Micrococcus luteus
List some frequent habitats for obligate anaerobes
- skin
- dust particles
Describe facultative aerobes
- do not require oxygen
- more efficient growth in its presence
- undergo aerobic respiration, as well as anaerobic respiration and fermentation
- E. Coli
Give a frequent habitat for facultative anaerobes
mammalian large intestine
Describe microaerophilic aerobes
- require oxygen at lower levels that atmospheric oxygen, so that they can complete aerobic respiration
- Spirillum volutans
Give a frequent habitat for microaerophilic aerobes
lake water
Describe the classification of anaerobes
- aerotolerant
- obligate
Describe aerotolerant anaerobes
- do not require a totally anoxic environment
- do not require oxygen to complete fermentation pathways
- Streptococcus pyrogenes
A frequent habitat for aerotolerant anaerobes is
the upper respiratory tract
Describe obligate anaerobes
- metabolise via anaerobic respiration or fermentation
- find oxygenic presence either harmful or lethal
- Methanobacterium formicicum
Frequent habitats for obligate anaerobes are
- sewage sludge
- anoxic lake sediments
How are compatible solutes acquired?
intake or synthesis
Describe nonphototrophic bacteria
- associated with glutamate and proline, sucrose and tehalose
- Escherichia
Describe freshwater cyanobacteria
- associated with glutamate and proline, sucrose and tehalose.
- Anabaena
Describe the Halotolerants with respect to their compatible solutes
sucrose and tehalose
Marine cyanobacteria
- Synechococcus
- associated with alpha-Glucosylglycerol
Marine algae
- Phaeocystis
- associated with Mannitol, various glycosides and dimethylsulphoniopropionate
Describe Halophilic photorophic purple bacteria
- Halorhodospira
- associated with Glycine betaine, ectoine and trehalose
Describe the Alphanothece
- salt lake cyanobacteria
- associated with Glycine betaine
Describe extremely halophilic archaea
- Halobacterium
- associated with potassium chloride
Describe Salinibacter
associated with potassium chloride
Describe Haloalkaliphilic archaea
- Natrinema
- associated with potassium chloride
Describe Halophilic green algae
- Dunaliella
- associated with glycerol
Describe the the Xerophilic and omsophilic yeasts
- Zygosachharomyces
- associated with glycerol
Describe the Xerophilic filamentous fungi
- Xeromyces
- associated with glycerol.
How do bacteria control growth?
recognising cell density
How do Gram negative bacteria recognise cell density?
- quorum sensing
- activator protein activated by an AHL
- interacts with the chromosomes to produce quorum-specific proteins
- interacts with AHL synthase, producing further AHL
- creates a self-amplifying feedforward loop
Describe AHLs
the group of intracellular esters acyl homoserine lactones
Describe a quorum
a level of high enough cell density
Describe quorum sensing
- synthesising AHLs of varying alkyl side chain length
- activate gene expression once a quorum is reache
- can be important for pathogenicity
Describe cell density recognition in the bioluminescent bacteira Aliivibrio fischeri
- AHLs control expression of the luxCDABE operon
- AHL-binding to the lux regulator LuxR activates transcription of the lux inducer LuxI
- once a quorum is reached, bioluminescence is switched on.
What is LuxI?
AHL synthase
How do Gram positive bacteria control growth?
using peptides
Describe the stringent response
- arises from cessation or downshift of prokaryotic growth
- (p)ppGpp synthesis reduces tRNA and rRNA synthesis
- activation of amino acid biosynthetic operons (if this is the factor behind growth halt)
- cell division arrest
- increases cellular stress responses
What generally causes cessation or downshift in prokaryotic growth
transfer from rich to a poor medium, oxygen mutation or carbon limitation
(p)ppGpp
guanine penta- or tetraphosphate
Describe the heat shock response
- several HSPs tasked with refolding denatured proteins
- HSP70 preoccupied with refolding denatured proteins
- leaving RpoH sigma factor to accumulate and complete its function of heat shock gene transcription
HSPs
- Heat Shock Proteins
- e.g. HSP60, HSP10
HSP60
also known as GroEL
HSP10
also termed GroES
HSP70
- also known as DnaK
- degrades RpoH sigma factor
Describe the amino acid starvation pathway
under amino acid starvation, injured tRNAs bind to the ribosome and stall their tRNA and RRNA synthesis
