Bacterial Growth Flashcards
What are the methods to determine bacterial growth?
determination of cell number
- total cell count = by microbiologist using a microscope
- coulter counter
viable cell count
- identify number of actively growing or dividing cells in a sample = grow a known volume on a nutrient medium
- must be diluted to stop overlapping of colonies and inaccurate count
- plate count method (colony becomes visible) = spread plate, pour plate = count the number of colonies, calculate concentration by multiplying the count with the known volume
determination of cell mass
- dry weight measurement = weigh after water has been removed
- turbidity = more cells means higher turbidity resulting in a cloudier/opaque/less transparent solution = convert the detected turbidity into concentration using spectrophotometer
determination of cell constituents
- measure specific constituents = example - DNA
What is colony forming unit (CFU)?
CFU is used to estimate the concentration of microorganisms in a sample
- it is a measure of viable cells in which a colony represents an aggregate of cells derived from a single progenitor cell (original cell)
- used to determine the number of viable bacterial cells in a sample per ml = concentration
How is the CFU calculated from an agar plate?
the number of visible colonies present on an agar plate can be multiplied by the dilution factor to get the CFU
- gives the number of viable bacteria cells in a sample per ml = concentration
What are the three types of bacteria and the optimal temperatures they grow at?
psychrophile = less than 20
- capable of growth and reproduction at low temperatures
mesophile = 16-40
- capable of growth at medium temperatures
thermophile = more than 40
- capable of growth at high temperatures
What happens to bacteria at low and high temperatures? What happens to bacteria at 37 degrees Celsius?
at low temperatures bacteria are dormant
at high temperatures bacteria are killed = denatured
at 37
- most bacteria/pathogens multiply quickly
- as temperature rises above and drops below, growth slows down
What are photoautotrophs and photoheterotrophs?
photoautotrophs
- make their own food and energy by photosynthesis
- use light (sunlight) as their energy source
- use carbon dioxide as their primary carbon source
- can fix carbon = convert inorganic carbon into organic carbon for use in cellular functions = biosynthesis, respiration
photoheterotrophs
- depend on organic matter already produced by other organisms for nourishment (nutrients)
- use light as their energy source
- use organic compounds as their primary carbon source
What are chemoautotrophs and chemoheterotrophs?
chemoautotrophs
- make their own food and energy = obtain energy for this from the oxidation of electron donors (inorganic compounds) in their environment
- use inorganic compounds as their energy source = hydrogen, ammonia, hydrogen sulphide
- use carbon dioxide as their primary carbon source
chemoheterotrophs
- depend on organic matter already produced by other organisms for their nourishment (nutrients)
- use organic compounds as their energy source
- use organic compounds as their primary carbon source
What are inorganic compounds?
lack carbon and hydrogen
What are growth factors? What are the different categories of growth factors?
growth factors are required in small amounts to fulfil specific roles in biosynthesis
can be synthesised using their own carbon source = does not require an outside source
- purines and pyrimidines = required for the synthesis of DNA and RNA
- amino acids = required for protein synthesis
- vitamins = needed as coenzymes and functional groups of certain enzymes
Why are growth factors needed?
the need for growth factors is a result of blocked or missing metabolic pathways in the cells
they are not needed by all bacteria
What is the symbol for water activity?
What are
- halophiles
- osmophiles
- xerophiles
water activity = Aw
pure water = Aw of 1.0
- decreases as water becomes more concentrated
halophiles - require NaCl for growth = thrive in high slat concentrations, low Aw
osmophiles - thrive in environments with high osmotic activity = high sugar concentrated environments
xerophiles - thrive in dry environments = low water activity/availability
What are the different types of anaerobes?
obligate anaerobes
- require oxygen for growth
obligate anaerobe
- do not need or use oxygen as a nutrient source
- harmed by presence of oxygen
facultative anaerobes/ facultative aerobes
- organisms that can switch between aerobic and aerobic types of metabolism
- can growth with or without oxygen
aerotolerant anaerobes
- bacteria with exclusively anaerobic type of metabolism = fermentation
- are insensitive to oxygen = can tolerate its presence
How do anaerobes and aerobes prevent the lethal accumulation of hydrogen peroxide and superoxide?
hydrogen peroxide and superoxide are produced by leaks of electrons from the mitochondrial electron transport chain
aerobe hydrogen peroxide is removed by - catalase = decomposes it superoxide is removed by - superoxide dismutase = prevents accumulation
anaerobe
- lack superoxide dismutase and catalase
- undergo lethal oxidations by various oxygen radicals
What are the three types of bacteria and the optimum pH they grow at?
What are the range of pH that an organism grows over defined as?
acidophiles - less than pH 7
neutrophiles - neutral pH = 5-8
alkaliphiles - more than pH 7 = grow slowly at pH 6/7 and optimum is pH 9
range of pH is defined as
- minimum
- maximum
- optimum
What is binary fission?
asexual reproductor by the separation of a body into 2 bodies = 2 identical daughter cells (identical to the parent cell)
- growth of cell = usually by lengthening
What is the process of binary fission?
1 - cell growth = elongates
2 - replication of chromosomes begins at the origin of replication = continues into both directions at once (bidirectional)
3 - FtsZ proteins migrate to the centre of the cell
4 - duplicated chromosome separate and move to the opposite ends of the cell. FtsZ proteins form a ring around the periphery of the midpoint of the chromosomes
5 - FtsZ directs the formation of the septum that divides the cell. Plasma membrane and cell wall material accumulate.
6 - once the septum is formed, the cell pinches into two and separates
7 - two identical daughter cells have been formed. FtsZ is dispersed throughout the cytoplasm of the cells
FtsZ - cell division protein
What is sporulation?
survival mechanism
formation of endospores by vegetative cells
- initiated when conditions for growth of vegetative cells become unfavourable
What is germination? What are the three steps?
germination
- endospores can remain dormant for years but when conditions allow they can convert back to vegetative cells rapidly
germination has three steps
1 - activation
2 - germination
3 - outgrowth
What are endospores?
formed from vegetative cells
- formed within the intracellular compartment of the mother cell
- mother cell does not survive, only the spore does
preserves the genetic material of the bacterial cell
What are the steps for sporulation?
1 - DNA replicates and extends into the axial filament = across the whole cell
2 - asymmetric separation
- forespore gets one copy of the DNA and the mother cell gets one copy = move to opposite poles
- septum forms asymetrically, closer to the forespore
3 - engulfment and protoplast formation
- mother cell engulfs the forespore and forms a second membrane around it = double membrane
4 - cortex formation
- peptidoglycan cortex forms between the membrane of the original forespore and the mother cell
5 - dipicolinate acid is synthesised and calcium is incorporated into the spore coat
- addition of calcium removes water = dehydration, as a result heat resistance increases
6 - coat formation
- proteins forms around the cortex = spore coat
- spore becomes mature
7 - lysis
- mother cell undergoes lysis/ disintegration of the chromosomes and releases the spore
What are the stages of bacterial growth?
1 - lag phase
- no increase in cell number = bacteria are preparing for reproduction and DNA synthesis
- increase in cell size only
2 - log phase = exponential phase
- increase in cell/bacterial number
- bacterial biomass increases linearly with time
3 - stationary phase
- number of bacteria reaches maximum
- no further increase in cell number = metabolic rate is decreased as metabolic products accumulate
growth rate = death rate
4 - death phase
- number of viable bacteria begin to decline
- no further divisions
