Bacterial Metabolism & Growth Flashcards
Microbial Metabolism - how it differs and is similar to eukaryotes
- Have many of same pathways for synthesis of compounds and energy generation as eukaryotes
- Do have a greater diversity of pathways
- it is the enzyme systems that determine the substrates that can be utilised
- substrates absorbed/transported from immediate enviro - they release extracellular enzymes to digest surrounding complex chemicals into smaller molecules that can be absorbed across cell membrane
- many of their extracellular enzymes toxic to tissue
Alternate substrates for Glycolysis
- Many bacteria don’t use glucose
- other substrates = other sugars (monosaccharides), disaccharides & polysaccharides, glyeral & fatty acids, proteins & aa
- principle: alternative substrate is converted in fewest steps into intermediate in main pathways for glucose catabolism
- often pyruvate or acetyle CoA
Difference between Fermentation and Respiration
Respiration: uses an external electron acceptor to oxidize substrates completely to CO2
-i.e. molecule that is from external enviro.
Fermentation: final electron acceptor is internal by-product of catabolism (i.e. lactate)
Cellular Respiration - definition
-Is the flow of electrons through or w/in a membrane, from reduced coenzymes to an external electron acceptor usually accompanied by the generation of ATP (pumping of protons across membrane and back through ATPase)
- coenzyems such as FAD and coenzyme Q involved
- terminal e- acceptor Oxygen - reduced to water (in aerobic)
- Alternate electron acceptors: nitrate, sulfate, methane
Secretion of metabolites
- effect
- 3 examples
- proteins and other cell metabolites actively secreted by variety of diff. secretory systems
- Secretion of metabolites has important functions in pathogenicity
Secretion of enzymes such as;
- Proteases
- Nucleases
- Phospholipases
- some can cause important tissue damage
Why knowledge of bacterial metabolism import.?
-Selective & differential media
- can make specific growth media that favours certain bacterium
- can add substrate that is used by one
Selective media: particular substrates added that only particular bacteria
Differential media: components put into media that changes in response to by-products (i.e. pH indicator)
Regulation of Metabolism
-Have similar systems to regulate production & activity of their enzymes
- Regulation of enzyme activity by feedback - product inhibition of enzymes allows rapid feedback - regulation via transcription is longer term control
- Regulation of enzyme production, 2 ways;
i) Repression: excess end product interacts w/ repressor protein (that is always active) and become active - ceases production of that product
ii) induction: repressor protein inactivated by substrate, which allows transcription & therefore enzyme production
Two component regulatory system
- Enables bacteria to respond to external enviro changes
- intracellular DNA binding proteins that regulate appropriate transcription
Microbial Growth (2 types)
- Either;
1. Growth of individual cells by;
i) Asymmetric budding
ii) Binary fission (membrane folds and cell separates into 2 equal sized bits - Can be very quick
2. Population growth: most significant for effects on other organisms
Bacteria Cell growth & division (3 steps)
- DNA replication - starts at a point of origin on ds chromosome & proceeds in opposite directions for each strand
- chromosome associated w/ cell membrane - so when cell begins to separate, two DNA dragged apart
- is semi-conservative - Cell elongation
- Cell division
Population growth
-typical growth curve
-Large populations of microorganisms can overwhelm defence mechanism of a host
-Growth exponential
Typical growth curve:
1. Lag phase: cells alive, but population not increasing
-is a period of adjustment (may need to induce some genes)
2. Exponential Phase: cells growing and dividing at constant rate
-young cells usually most infective at this stage
3. Stationary Phase: population stops increase due to nutrient depletion, pH change, lack of O or build up of toxic compounds
4. Death/Decline stage: cell death > cell division - usually due to same factor that caused population to enter stationary phase
Rate of Growth
Measured by Mean Generation time (MGT)
-Depends on species, type of growth medium and enviro. conditions
Continous culture
- “chemostat” or fermentor
- continous culture that continually supplies new substrates and removes end products
- can be sustained for years
- used when people want to study microbial evolution
Measure measurement of growth (5)
- Total cell count: viable + dead
- Direct count: using a counting chamber - count every cell
- Viable cell count: miles and misra method, pour plate technique or filtration technique
- Electrical resistance
- Microbial mass (cell densities, wet weights, dry weights)
- Nitrogen determination: nitrogen content can be used to estimate amount of protein which therefore = bacterial numbers
Methods to count colonies
- miles & misra
- Pour plate
- Filtration
- Miles and Misra: dilution of suspension, put small volume on agar plate, grow and count colonies
- can work out number - Pour plate technique: bacterial dilutions suspended in molten agar - incubate, grow and count
- Filtration technique: useful w/ small no. of bacteria in large volume of water
- bacteria trapped on filter then filter incubated on plate
