L8: bacterial growth

name 5 parameters important for bacterial growth

temperature, pH, osmotic pressure, nutrients, oxygen

what is defined as the minimum temperature

point at which membranes start to gel

what is defined as the optimum temperature

enzymatic reactions occurring at the maximum possible rate

what is defined as the maximum temperature

protein denaturation + collapse of cytoplasmic membrane

what are the 4 classes of microorganisms by temperature

psychrophile

mesophile

thermophile

extreme thermophile

what temperature do psychrophiles grow under

~ 0-20 °C

what temperature do mesophiles grow under

~ 12-45 °C

what temperature do thermophiles grow under

~ 40-80 °C

what temperature do extremethermophiles grow under

~ 62-106 °C

define cell properties allowing growth at cold temperatures

increased membrane fluidity: higher content of unsaturated FAs + shorter acyl-chain length

production of anti-freeze proteins: bind to small ice crystals to inhibit their growth by covering water-accessible surfaces of ice

production of cryoprotectants (trehalose + exopolysaccharides)

production of cold adapted enzymes: higher proportion of helices, less weak bonds + interdomain interactions for greater flexibility

define cell properties allowing growth at high temperatures

genome protection (stabilisation of DNA by DNA-binding proteins, introduction of supercoils by reverse DNA gyrases. resistance to denaturation favoured by high G-C%)

membrane modified with ether-linked phospholipids + single lipid layer

production of thermostable proteins (hydrophobic interactions + increased proportion of ionic interactions

thermostable charonins

what are the metabolic adaptations of acidophiles

respiratory chains pump H⁺

what are the metabolic adaptations of alkaliphiles

respiratory chains pump Na⁺

what are the 4 classifications of osmotic pressure impacting bacterial growth

nonhalophile

halotolerant

halophile

extreme halophile

what cell properties create adaptation to osmotic conditions

regulation of water movement by passive diffusion + aquaporins

production of compatible solutes (betaine, proline, glutamic acid, etc.)

release of solutes by mechanosensitive channels

why is salt required in halophiles

S-layer glycoproteins stabilised by Na⁺ ions

accumulation of K⁺ as a compatible solute

what 3 key things do all bacteria require for growth

energy source

electron source

carbon source

what other molecules do bacteria require

nitrogen, sulphur, phosphorous, some vitamins,

cofactors (K+, Ca2+, Mg2+),

trace elements (Fe, Cu, Zn)

what is ROS

reactive oxygen species: oxygen derivitaves

what are the 3 toxic forms of oxygen ROS

superoxide

hydrogen peroxide

hydroxyl radical

what 3 enzymes detoxify ROS

catalase / peroxidase

superoxidase dismutase + catalase

superoxide reductase + catalase

how does catalase detoxify ROS

converts H₂O₂ into H₂O

how do superoxide dismutase + reductase detoxify ROS

convert O₂^- into H₂O₂

what are the 5 types of oxygen requirements in bacteria

obligate aerobes : exclusively use O2 for respiration

facultative aerobes : can use O2 for respiration

microaerophiles : require O2 for respiration

anaerobic aerotolerant : don’t use O2 for respiration

obligate anaerobes : damaged/killed by O2

describe the properties underpinning oxygen requirements/resistance

presence of catalase + SOD:

obligate aerobes + faculative aerobes contain catalase + SOD, anaerobes aerotolerant contain only SOD

what are the 2 types of bacterial growth measurements

direct measurements + indirect measurements

what are the direct measurements for bacterial growth

flow cytometry,

microscopic counts,

viable counting

what are the pros + cons of using microscopic counts

can work backwards to find the concentration of bacteria

fastidious + imprecise, count both live + dead cels

what are the pros + cons of using viable counting

can calculate viable CFU concentrations

bias for bacteria with long chains (can be worked around)

what are the pros + cons of using flow cytometry

creates graph + can be used to measure number of cells, morphology, + populations. can discriminate between live + dead cells

what are the indirect measurements of bacterial growth

optical density

dry weight

metabolic activity

what are the limitations of optical density

requires high cell densities, doesn’t distinguish live vs dead cells, OD values differ depending on organisms, doesn’t work with molds + filamentous bacteria

what are the 4 phases on a bacterial growth curve

lag phase

log phase

stationary phase

death phase

in which part of the bacterial growth curve is metabolism starting but no division

lag phase

in which part of the bacterial growth curve is there an exponential increase in population

log phase

in which part of the bacterial growth curve is microbial deaths balancing production of new cells

stationary phase

in which part of the bacterial growth curve is the population decreasing

death phase