MICR221 Lecture 1 - Physical and Chemical Requirements of Microbial Growth Flashcards
what is microbial growth?
an increase in the number of cells that causes population growth
what is binary fission?
the division of a bacterial cell
what is the process of binary fission?
1 parent cell –> cell elongates –> chromosomal DNA replicates (2 copies of genetic material are in 1 cell for a short period of time) –> each chromosome moves to opposite ends of the elongated cell –> septum (special cross-wall) starts to form –> fully formed septum causes the elongated cell to divide into 2 identical daughter cells
what is the equation for cell growth?
2^n
what determines bacterial cell shape?
depends on the plane of division during binary fission
how is a diplococcus shape formed from a coccus shape?
coccus cell is divided into 1 plane to create a diplococcus cell (1–>2)
how is a streptococcus shape formed from a coccus shape?
coccus cell is divided into 1 plane to create a diplococcus cell and then the diplococcus cell is divided into 2 planes to create a streptococcus cell
how is a cluster shape formed from a coccus shape?
coccus cell is divided into many planes to create a cluster cell
why is a small bacterial cell shape more common among bacteria?
a small bacterial cell shape increases the surface area to volume ratio and this increases the uptake of nutrients in the cell supporting a rapid cell growth
how does a large bacterial cell shape increase surface area to volume ratio?
by having a convoluted plasma membrane
what are the 2 factors for the growth requirements of bacterial cells?
physical factors and chemical factors
what are the 4 physical factors of growth requirements?
gaseous atmosphere –> temperature –> pH –> osmotic pressure
what are aerobes?
cells that require oxygen for aerobic respiration
what are anaerobes?
cells that prefer the absence of oxygen for anaerobic respiration
what do aerobes use in terms of the electron transport chain?
use the electron transport chain with oxygen or another oxidant as the terminal electron acceptor
what do anaerobes use?
use the electron transport chain with an exogenous terminal electron acceptor such as nitrate and sulphate
what are facultative anaerobes?
cells that grow with or without the presence of oxygen
what is fermentation in terms of the electron transport chain?
generates no electron transport chain or proton motive force where ATP is synthesised from substrate-level phosphorylation
what is the electron acceptor in fermentation?
endogenous electron acceptor pyruvate
what are microaerophiles?
cells that require little oxygen
micro= little
what are capnophiles?
cells that require increased levels of carbon dioxide
what are the 5 oxygen concentrations (in terms of growth in test tubes)?
obligate aerobes facultative anaerobes aerotolerant anaerobes strict anaerobes microaerophile
what are obligate aerobes and what protective enzymes do they include?
cells that require oxygen
+ SOD and + Catalyse
what are facilitative anaerobes and what protective enzymes do they include?
cells that prefer oxygen
+ SOD and + Catalyse
what are aerotolerant anaerobes and what protective enzymes do they include?
cells that grow with or without the presence of oxygen
+ SOD and - Catalyse
what are strict anaerobes and what protective enzymes do they include?
cells that oxygen is toxic for
- SOD and - Catalyse
what are microaerophiles and what protective enzymes do they include?
cells that grow between 2-10% oxygen conc
where does bacteria grow if it is an aerobe in a test tube?
at the top of the test tube
where does bacteria grow if it is an anaerobe in a test tube?
at the bottom of the test tube
how is oxygen toxic to anaerobes?
oxygen can be converted by metabolic enzymes into highly reactive derivatives such as O2- which is a superoxide free radical and this damages cells. Anaerobes do not possess the protective enzymes to break down O2-
how to aerobes break down O2- (superoxide free radical)?
O2- is converted into hydrogen peroxide by the enzyme superoxide dismutase and then is further broken down by the protective enzymes catalase or peroxidase
how many protective enzymes will aerobes contain?
2/3 protective enzymes
what are the 5 types of bacteria based on their temperature preferences?
psychrophiles psychrotrophs mesophiles thermophiles hyperthermophiles
what temperature do psychrophiles grow?
below or around 10’C
what temperature do psychrotrophs grow?
around 25’C
what temperature do mesophiles grow?
around 35-40’C
what temperature do thermophiles grow?
optimum temp is above 45’C
what temperature do hyperthermophiles grow?
around 90’C
what pH do most bacteria grow at?
between pH 6-9
what is osmotic pressure?
determined by the number of molecules in solution
what is the most favourable environment for bacterial growth?
isotonic, when the bacterial cell contents have the same concentration as the surrounding medium
what are the 2 chemical factors for growth requirements?
water
energy and electron source
what does temperature affect?
affects the availability of water
what does water affect?
affects osmotic pressure
what are phototrophs?
derive energy from sunlight
what are chemotrophs?
derive energy from the oxidation of chemical compounds either organic or inorganic
e.g sugars or amino acids
what are lithotrophs?
reduced inorganic substances
what are organotrophs?
reduced organic compounds
what are autotrophs?
use only inorganic carbon in the form of CO2
what are heterotrophs?
utilise organic carbon - proteins, lipids and carbohydrates
what is the combined term for energy, electron and carbon sources?
chemo organoheterotrophs
what are chemo organoheterotrophs?
most non-photosynthetic microbes
what are aerobes?
cells that require oxygen for aerobic respiration
what do aerobes use?
use the electron transport chain with oxygen or another oxidant as the terminal electron acceptor
