Small is beautiful: challenges and consequences of life at the molecular level Flashcards
Describe unicellular life
interact directly with their environment, over which have limited control
Describe cardinal temperatures
for every microorganism there is:
- a minimum temperature below which growth is not possible
- an optimum temperature at which growth is most rapid
- a maximum temperature above which growth is not possible
Describe membrane gelling
transport processes so slow that growth cannot occur
Describe protein denaturation
- collapse of the cytoplasmic membrane
- thermal lysis
Describe mesophiles
- best studied and understood
- occur in the digestive tract of animals
- in terrestrial and aquatic environments in temperate and tropical latitudes.
- Escherichia coli
- most bacteria associated with humans
Describe E. coli
– optimum temperature for most E.coli: ~39 degreesC
– maximum is 48 degreesC
- minimum 8 degreesC
– temperature range: ~40 degreesC.
List some mesophilic bacteria
– Staphylococcus aureus
– Streptococcus pyogenes
– Neisseria meningitidis
Describe Psychrophiles
- optimal growth temperature of <15 degreesC or lower
- maximum growth temperature <20 degreesC
- minimum growth temperature of 0 degreesC or lower
- found in constantly cold environments
- often intolerant to warmer temperatures
- frequently grow in dense masses within and under sea ice in polar regions
Describe Psychrotolerant microbes
- can grow at 0 degreesC
- have optima of 20-40 degreesC
Describe Psychrophilic adaptations
- enzymes that function optimally in the cold
- high content of unsaturated and short chain fatty acids
- express Cold shock proteins
- express Cryoprotectants
- exopolysaccharide cell surface slime
Describe Thermophiles
growth temperature optima: >45 degrees C
Describe Hyperthermophiles
growth temperature optima: >80 degrees C
Describe the environments of Thermophiles and Hyperthermophiles
– terrestrial hot springs: >100 degrees C
– hydrothermal vents: >350 degrees C
Describe Methanopyrus
- methane procuring genus of archaea
- capable of growth up to 122 degrees C
Describe some adaptations to extreme heat
- genomic changes
- base biases
- gene expression
- protein thermostability
Describe the genomic changes of Thermophiles and Hyperthermophiles
- genes gained through HGT
- mutations
- genome reduction
Describe the base biases of Thermophiles and Hyperthermophiles
- highly stable gene structure
- high GC content (not universal)
- codon use biases
Describe the gene expression of Thermophiles and Hyperthermophiles
- stable and efficient protein synthesis
- temperature responses of gene expression
Describe the protein thermostability of Thermophiles and Hyperthermophiles
- more disulphide bonds
- stability of protein
complices
Describe reproduction by binary fission - the basics
- rapid
- efficient
- adapted for processes such as sporulation
Describe reproduction by binary fission - the specifics
- cell elongation
- genome replication
- separation of genomes
- formation of cleavage furrow
- cell wall forms in cleavage furrow
- septation
septation
separation
Describe some features of binary fission
- generates identical daughter cells,
- exponential growth (geometric increase in numbers)
- multiple genome replications per cell division (speeds up division rate)
- ‘feast and famine’ lifestyle
Describe E. coli division
A single Escherichia coli cell dividing every 33.3 minutes without nutrient limitation could reach the mass of the earth in less than 48 hours.
Describe the limitations to microbial size
- SA:V gets smaller as the cell gets larger,
- if a cell becomes too large, insufficient material can cross the membrane fast enough
- cell must divide to maintain favourable SA:V
- cell must maintain sufficient genetic and metabolic capacity to function
Describe rod-shaped bacterial size
- alter both their width and length to achieve a condition-dependent surface
- maintenance of a condition-dependent SA:V sets bacterial size.
- rates of volume and surface growth both scale with volume, producing SA:V homeostasis
- surface material accumulation threshold for division could underlie length control
… links surface growth rate to volume (in rod-shaped bacteria)
Biosynthesis of surface material in the cytoplasm
Define exponential volumetric growth
dV/dt alpha V
Define surface growth rate scaling with volume
dA/dt alpha V
if surface synthesis > volume synthesis
cell is smaller on average
if volume synthesis > surface synthesis
cell is larger on average
Describe nano- bacteria and archaea
- ‘filterable’
- 50-400nm
- abundant in biosphere
- oceans,riversand soils.
- mostly uncultured & characterised
- many likely non-cultivable
- very small genomes
- dependent on communities
Describe LSB
- large sulfur bacteria
- e.g. Thiomargarita magnifica
Describe Thiomargarita magnifica
- found attached to leaves in sulphur-rich waters in
mangrove swamps in Guadeloupe - almost 1cm
- large vacuole
- cytoplasmic layer only 2-3μm thick
- polypoid (~40,000 genome copies)
- grow relatively slowly
- two weeks to produce daughter cells
Describe the advantages of polyploidy
– enables local transcription and translation
- occurs in specialised Pepin structures
Describe the Gram-positive cell wall
- glycan chain
- S-layer glycoproteins
- peptidoglycan
- cytoplasmic membrane
- lipoteichoic acid
- teichoic acid
- polysaccharide
- lipoprotein
- cytoplasm
Describe the Gram-negative cell wall
- porins
- LPS
- outer membrane
- peptidoglycan
- lipoprotein
- periplasm
- cytoplasmic membrane
- cytoplasm
Describe the cell envelope of Sulfolobales
S-layer
Describe the cell envelope of Ignicoccus hospitalis
- outer membrane
- Ihomp1
- 24nm pore
Describe the cell envelope of Methanosphaera
pseudomurein
Describe the cell envelope of Methanothermus
- S-layer
- pseudomurein
Describe the cell envelope of Methanospirillum
- sheath
- S-layer
Describe the cell envelope of Methanosarcina
- methanochondriotin
- S-layer
Describe the bacterial cytoplasmic membrane
- 6-8 nm
- separates cytoplasm from the environment
- nutrients must be transported inwards, waste products outwards
Describe the pmf
- consequence of the electrochemical gradient across the membrane
- major source of energy transduction, including active transport ant ATP generation
Describe the roles of the cytoplasmic membrane in bacteria
- free energy source
- signalling and processing
- antibiotic resistance
- pH homeostasis
- cell division
- dynamic communication
- membrane transport
- ATP synthesis
- motility
Describe phototrophy
organism uses light as the energy source to catalyse biochemical reactions
Describe chemotrophy
organism uses chemical reactions (oxidation) as the energy source to catalyse biochemical reactions
Describe autotrophy
organism is capable of fixing carbon from non-biological (inorganic) sources.
Describe heterotrophy
organism must obtain carbon from biological sources.
List some methods of microbial motility
- swimming
- twitching
- gliding
- sliding
Describe sliding
movement by growth on a surface.
Describe the microbial motile environment
- viscous environment
- subject to molecular forces leading to Brownian movement
Describe bacterial swimming
individually and in swarms
Describe bacterial twitching
mediated by pilus retraction
Describe bacterial gliding
active movement across a surface
Describe the flagella
- one or more
- allow bacteria to swim
- originate in the cytoplasm beneath the cell wall
- extend beyond the cell
Describe monotrichy
- single flagellum at one pole
- e.g. Vibrio cholerae
Describe amphitrichy
- presence of a single flagella at each pole
- e.g. Spirilum
Describe lophotrichy
- tuft of flagella at one pole
- e.g. Pseudomonas
Describe peritrichy
- flagella all over the surface
- e.g. E. coli
Non-motile bacteria that lack a flagella are called
atrichous
How to bacteria avoid unfavourable environments
resting stages
Describe endospory
produced by Gram positive bacteria
Describe Gram positive endospores
- highly resistant to heat, desiccation and radiation
- stable for many years, decades, perhaps centuries
- major reason for difficulties in sterilisation processes
- important in medicine and the food industry
Describe the bacterial vegetative cycle
- growth
- medial division
Describe bacterial sporulation
- polar division (prespore and septum, mother cell)
- asymmetric cell division
- engulfment
- cortex (+ cell wall and membrane)
- spore coat
- maturation and cell lysis
- germination
Describe biofilms
- association with surfaces forming biofilms
- composed of single microbes or complex communities
- various relationships, antagonistic, cooperative, or neutral
- complex biological processes: crucibles of evolution
Describe biofilm formation
- reversible attachment to surface
- irreversible attachment
- maturation: EPS and cell cluster
- microcolonies
- dispersion
Microbes exhibit
little or no homeostasis.
Name some factors microbes have to tradeoff
size, metabolic & genetic complexity, and growth rate.
