Lecture 1 Flashcards
Physical + Chemical needs for microbial growth
explain the process of binary fission
firstly the cell elongates (duplicates genetic material) before a septum forms in the middle. the cell separates once the septum fully forms
cell numbers increase….. (binary fission)
exponentially 2*n
how to different cell arrangements occur
through what plane the cell divides
- divisions in one plane = chain
- divisions in many planes = cluster
how does the shape affect a bacteria cell
small cells are better for bacteria as being small increases the surface to volume ratio
what are the 4 PHYSICAL factors for growth
gaseous atmosphere
temperature
pH
osmotic pressure
what are the 4 CHEMICAL factors for growth
water
energy and electron source
carbon
macro and micronutrients
aerobes
require molecular oxygen
- electron transport chain, then final electron acceptor is oxygen (o some other oxidant)
‘strict’
anaerobes
prefer the absence of oxygen
- uses electron transport chain, the ifnal electron acceptor is EXOGENOUS
- eg nitrate, sulphate
- in fermentation, no electron transport chain (or generation of PMF), ATP is synthesized by substrate-level phosphorylation, electron acceptor is ENDOGENOUS
- eg pyruvate
facultative anaeraobes
grow with or without oxygen but will grow better with oxygen (quicker metabolic rate)
microaerophiles
requires a little bit of oxygen (not too much)
- 2-10% preferred oxygen (less than atmospheric)
capnophiles
require increased levels of carbon dioxide (over atmospheric)
how can oxygen be toxic?
it can be converted by metabolic enzymes into highly reactive derivatives such as superoxides free radicals (O2) - damaging to cells (but gets converted by enzymes in aerobes)
- anaerobes do not posses enzymes and cannot tolerate oxygen
minimum temperature…
slows growth
mean generation time is loooong
enzymes may not work
fluids get thick
optimum temperature…
most rapid speed of growth
growth occuring at its best
maximum temperature…
cells are killed above this
what are the 5 temperature variants microbes may be categorised in
(lowest to highest temp)
psychrophiles
psychrotolerants
mesophiles
thermophiles
hyperthermophiles
____ grow in near human body temperature and can cause____
mesophiles, disease
what are the 4 osmotic pressure variants microbes may be categorised in
(lowest salt to most salt)
nonhalophile
halotolerant
moderate halophile
extreme halophile
what happens to microbes in a hypertonic solution (general)
water moves out of bacterial cell
- plasmolysis
- cytoplasmic membrane pulls away from cell wall (death)
what happens to microbes in a hypotonic solution (general)
water molecules move into cell - bacterial cell wall becomes rigid (doesnt pop)
what osmotic pressure is favourable?
isotonic
why is water a chemical factor for growth
bacterial cells = 90%
- carries dissolved nutrients
- transports toxins out
- affected by temp
- affects osmotic pressure
what are the 2 categories organisms can be divided into based on its energy source
phototrophs (energy from light_
chemotrophs (energy from oxidation of chem compounds - organic/inorganic)
- eg sugars, amino acids
electron source may be from…
reduced inorganic substances = lithotrophs
reduced organic compounds = organotrophs
