Lecture 1 - Physical and chemical requirements of microbial growth Flashcards
Bacterial growth is
exponential
Population =
2^n where n is the division number
The time it takes for one cell (and therefore the whole population) to divide is called the …
Mean generational time (doubling time)
Why is it better to put microbial growth as logarithmic compared to arithmetic?
On graphs usually plotted as a log10 number of cells to produce a straight line - also as exponential curve has its disadvantages such as it being difficult to separate plot points at the beginning of the population growth and as the population numbers get high it is hard to plot them
Logarithmic scale easier to read than the arithmetic (exponential) curve
Binary fission steps
Elongation - DNA replication - Cross wall forms (septum) - two cells separate
There are two copies of the genetic material in one cell just before the septum forms. The chromosome migrates, one to each end of the cell and when the septum completely forms the cells separate and this is the end of one cycle of binary fission
End up with two identical daughter cells
Surface area to volume ratio
Small cell increases SA:V ratio
As the SA:V ratio increases, the uptake of nutrients become more efficient which therefore supports a rapid growth rate
Larger bacteria do exist but often use different characteristics such as a convoluted surface to maximise the SA:V ratio
Cocci
Roughly spherical cells - can exist singly or can be in an arrangement
Diplococci
Diplococci arise when cocci divide and remain together to form pairs.
Chains: streptococcus
Long chains of cocci result when cells adhere after repeated divisions in one plane; this pattern is seen in the genera Streptococcus, enterococcus and lactococcus
Clusters
Members of the genus staphylococcus divide in random planes to generate irregular, grape-like clusters
Rods
sometimes called bacilli (singular = bacillus) differ in length to width ratio
Organisms can be divided into two categories according to their energy source …
Phototrophs = derive energy from sunlight Chemotrophs = energy derived from oxidation of chemical compounds (organic or inorganic) e.g. sugars, amino acids
Phototrophs
derive energy from sunlight
Chemotrophs
energy derived from oxidation of chemical compounds (organic or inorganic) e.g. sugars, amino acids
Electron sources..
Reduced inorganic substances = lithotrophs
Reduced organic compounds = organotrophs
Carbon sources…
Autotrophs = utilise only inorganic carbon in the form of carbon dioxide Heterotrophs = utilise organic carbon (proteins, carbohydrates and lipids)
Lithotrophs
Reduced inorganic substances
Organotrophs
Reduced organic substances
Autotrophs
Utilise inorganic carbon in the form of carbon dioxide
Heterotrophs
Utilise organic carbon (proteins, carbohydrates and lipids)
chemoorganoheterotrophs
= uses organic energy sources
List the physical requirements of microbial growth
Gaseous atomosphere (oxygen)
Temperature
pH
Osmotic pressure
List the chemical requirements of microbial growth
Water
energy and electron source
Carbon
Macronutrients and micronutrients
Cardinal temperatures
Minimus below which growth is not possible (~8 degrees), optimum where growth is most rapid (~37 degrees), and maximum above which growth is not possible (~65 degrees)
Minimum temperature may kill but is more likely to send the microbe into a protective dormancy phase (slows everything in the cell down), whereas maximum temperature kills
pH
Bacteria usually like a neutral range (6-9) (fungi are a bit wider), each bacteria has an optimum pH for its extracellular environment
Always exceptions to the rule such as acidophiles and archaea
Buffers are often put in growth media to keep the pH near neutral because that is what most of the microbes like
Acidophiles = growth optimum between pH 0-5.5
Neutrophiles between pH 5.5 and 8.0
Alkaliphiles between pH 8.0 and 11.5
Acidophiles
growth optimum between pH 0-5.5
Neutrophiles
growth optimum between 5.5-8
Alkaliphiles
Growth optimum between 8-11.5
What is osmotic pressure determined by?
the number of molecules in solution
Isotonic
bacterial cell contents have the same concentration as the surround medium (most favourable)
Hypertonic
high concentration outside the cell which draws water out of the cell, causes shrinkage of the membrane and plasmolysis which kills the cell
Hypotonic
low concentration outside the cell which draws water into the cell, cell expands however the cell does not burst due to the rigid cell wall
Some microbes are adapted to extreme hypertonic environments and can be called
oenophiles
______ require the presence of NaCl at a concentration above about 0.2M
halophiles
Water
Affects osmotic pressure and temperature affects the availability of water
Essential for bacterial growth, accounts for 80-90% of the bacterial cell
Energy and electron source
important for essential cell functions
Carbon
Half the dry weight of a bacterial cell is carbon
Aerobes
Require molecular oxygen (aerobic respiration) (required for their growth and metabolism)
Completely dependent on atmospheric oxygen for growth
Electron transport chain, then final electron acceptor is oxygen (or some other oxidant)
Anaerobes
Prefer the absence of oxygen (anaerobic respiration or fermentation)
Anaerobic respiration uses the electron transport chain, the final electron acceptor is exogenous e.g. nitrate, sulphate
Use glove box when you want to investigate microorganisms in an anaerobic environment
Obligate anaerobes do not tolerate oxygen and die in its presence
In fermentation there is no…
ETC (or generation of proton motive force), ATP is synthesised by substrate level phosphorylation, electron is endogenous e.g. pyruvate
Facultative anaerobes
grow with or without oxygen - better with oxygen, they use oxygen when it is present but are able to continue growing by using either anaerobic respiration or fermentation when no oxygen however the efficiency of producing energy decreases in the absence of oxygen
Microaerophiles
require a little oxygen but not too much (ideal conc is between 2-10%, there is 20% oxygen conc in the atomsphere)
Capnophiles
require increased levels of carbon dioxide (atmosphere is at 0.4%, they like 5% therefore 100 times more CO2 than in the environment)
Aerotolerant anaerobe
grows equally well with or without oxygen
Toxic oxygen
Oxygen can be converted by metabolic enzymes into highly reactive derivative such as the superoxide free radical (O2-), which is very damaging to cells (damage proteins, lipids and nucleic acids). Aerobes and most facultative organisms convert superoxide free radical to hydrogen peroxide by means of the enzyme superoxide dimutase. This is further broken down by catalase or peroxidase. Anaerobes do not possess these enzymes and therefore cannot tolerate oxygen
Superoxide and hydrogen peroxide are often referred to as “reactive oxygen species (ROS)”
Toxic products of oxygen reactions
O2 + e- -> O2- (superoxide radical)
O2- + e- + 2H+ -> H2O2 (hydrogen peroxide)
H2O2 + e- + H+ -> H2O + OH- (hydroxyl radical)
aerobes and faculatative organisms produce protective enzymes:
superoxidedimutase (2O2- + 2H+ -> O2 + H2O2)
catalase (2H2O2 -> 2 H2O + O2)
peroxidase (H2O2 + NADH -> 2H20)
Psychrophiles
like low temperatures, grows at 0 degrees and has an optimum growth temperature of 15 degrees or lower (e.g. arctic, antarctic, deep ocean water)
Psychotrophs/psychotolerants
low temps, optimum is 20 degrees, may be responsible for food in the fridge spoiling (can grow around 0-7 degrees, max at around 35 degrees)
Mesophiles
optimum temp around 37 degrees (between 20 and 45 degrees), lots of study done because it includes human pathogens
thermophiles
optimum 60 degrees, compost sites or spas or hot water cylinders for example
Hyperthermophiles
optimum approx 90 degrees, e.g. volcanoes, very hard to replicate these conditions in the laboratory
Macronutrients
Macronutrients are necessary in large amounts; micronutrients tend to be needed in smaller amounts and are often trace elements.
Macroelements/nutrients = carbon, hydrogen, nitrogen, oxygen, phosphorus, sulphur (CHONSP - these elements make up 96% of all living organisms)
Found in organic molecules such as lipids, proteins etc
Other macro elements listed below. They exist as cations and anions and generally are associated with and contribute to the activity and stability of molecules and cell structures such as enzymes and ribosomes. Thus they are important in many cellular processes including protein synthesis and energy conservation.
Cations = potassium, sodium, magnesium, calcium, iron
Anion = chlorine
Micronutrients
Micronutrients = zinc, cobalt, molybdenum, copper, manganese
Aid in catalysis of reactions and maintenance of protein structure
Oxidation
Loss of electrons = oxidised
OIL = Oxidation is loss
The thing that is oxidised is the reducing agent/provides reducing power
Reducing agent
The thing that is oxidised is the reducing agent/provides reducing power
Reduction
Gains electrons = reduced
RIG = Reduction is gain
The thing that is reduced is an oxidising agent/provides oxidising power
Oxidising agent
The thing that is reduced is an oxidising agent/provides oxidising power
Oxidant
the oxidant or oxidizing agent gains electrons and is reduced.
Reductant
the reductant or reducing agent loses electrons and is oxidized
