Microbe-Environment Interactions Flashcards
What are extremophiles?
Species which can survives under extreme conditions
How are microbes classified?
By temperature
By pH
By growth in salt
By effect of oxygen
What is minimum growth temperature?
The lowest temperature a species will grow at
What is maximum growth temperature?
The highest temperature at which growth is possible
What is optimum growth temperature?
The temperature at which the species grows best
What happens to growth rate above optimum growth temperature and why?
It declines rapidly because higher temperatures denature enzymes required for growth
What are organisms pH range?
2-3 units
What type of pathogens can tolerate low pH’s? Give an example.
Enteric pathogens
E.coli
What are neutrophils optimum growth pH?
5.5-8
What pH is referred to as optimum pH?
External pH
What pH must internal cells be maintained at?
pH 5-9
How much salt is in sea water?
3%
Requirement for salt is absolute. What does absolute mean?
It cannot be replaced by other ions
What are non-halophiles?
Microbes that do not grow well in salty conditions
What are halophiles?
Microbes that can tolerate salty conditions to a certain extent
What are moderate halophiles?
Microbes that grow well in salty conditions
What are extreme halophiles?
Microbes that thrive in salty conditions
What are obligate aerobes?
Microbes that require oxygen to survive
What are obligate anaerobes?
Microbes that are harmed by oxygen
What are facultative anaerobes?
Microbes that use oxygen when it is present but can grow without it
- Fermentation
- Anaerobic respiration
What are microaerophilic microbes?
Those which require oxygen but at lower levels than atmospheric oxygen
What are aerotolerant microbes?
Those which can not use oxygen for growth but are unaffected by its presence
- Respire anaerobically
When are superoxide free radicals produced?
During aerobic respiration
Why are superoxide free radicals toxic?
Because they are chemically unstable
How do organisms that grow in atmospheric oxygen cope with toxic superoxide free radicals?
Superoxide dismutase (SOD) neutralises O2- Catalase converts toxic H2O2 to H2O
What environmental factors influence microbial growth?
Carbon sources Oxygen Temperature pH Salinity Water availability Sunlight (UV radiation) Predation
What are the problems surrounding microbial survival in high temperatures?
Proteins denature
Small molecules are unstable
DNA helix unwinds at high temperatures
Membrane become more fluid
How might protein structure change in order to increase thermodynamic stability?
Proteins may fold differently
What property of amino acids lowers their tendency to unfold?
Hydrophobic core
What type of proteins might cells contain in order to protect themselves from high temperature?
Heat shock proteins
- Refold denatured proteins
What do cells contain that help DNA to remain coiled and functional in high temperatures?
Enzymes and DNA repair proteins
- Reverse DNA gyrase
Histone-like proteins and additional DNA binding proteins
Name a solute found in the cytoplasm that prevents unwinding and chemical damage of DNA.
Di-glycerol phosphate
How might membranes change in order to reduce fluidity?
More saturated and longer fatty acid chains
- These molecules pack more tightly making the membrane more stable
What do archaeal cell membranes lack?
Lipids
What are the problems surrounding microbial survival in low temperatures?
Decreased enzymatic activity
Lower metabolic activity
Slow rates of ion transport and diffusion
How might membranes change at low temperatures?
Increased unsaturated and shorted chain length fatty acids = more fluid
Increased proportion of cyclic fatty acids
What types of proteins are produced at low temperatures? Give three examples
Cold shock proteins - RecA = involved in DNA repair - Hsc66 = maintains protein conformation - CspA = transcriptional factor Antifreeze proteins
What is the main problem surrounding microbial survival at low pH?
Maintaining pH homeostasis inside cells (pH 5-7)
What are aminophospholipids are how might they be affected at low pH?
Increased number
- They make membranes more positively charged
How are proton pumps affected at low pH?
Activated
How does membrane permeability to protons change at low pH?
Less permeable
- H+ influx inhibited by positive membrane potential
How is the number of membrane channels affected at low pH?
Reduced size and number of membrane channels
What cytoplasmic buffering molecules are produced at low pH?
Sugars
Amino acid derivatives
What is the main problem surrounding microbial survival at high salt concentrations?
Osmoregulation = maintaining turgor pressure inside cells
How does the cell protect proteins and enzymes at high salt concentrations?
Accumulation of K+ instead of Na+
Why is salt excluded from the cytoplasm at high salt concentrations and what is it replaced with?
Replaced with organic compatible solutes which do not interfere with enzymatic function
What is the main problem surrounding microbial survival at low water contents?
Desiccation = water loss
What do cells produced at low water contents?
Extracellular matrix (capsule) Osmoprotectants = trehalose More DNA repair proteins
What are xerophiles?
Organisms that are adapted to live in environments with low water activity
How can the growth of pathogens be controlled artificially?
By altering their certain aspects of their environment;
- Heat
- Cold
- Acidity
- Water activity
- Chemicals
How is pathogen growth altered by heat?
Heat kills microbes by denaturing proteins and enzymes
Heat preserved canned goods are a good method of food preservation
What are the different ways in which heat can be altered in a pathogens environment?
Moist heat - Boiling - Steaming Pasteurisation Dry heat - Flaming - Sterilisation
How is pathogen growth altered by cold?
Microbes can be killed when ice crystals disrupt their cell membrane
Usually cold temperatures slow or stop microbial growth
What microbe is the exception and is not affected by cold temperatures?
Listeria monocytogenes
- Food borne bacterial pathogen
- Can grow at 4 degrees
What temperature are microbes preserved at in labs?
-80 degrees with glycerol which acts as a cryptoprotectant
How is pathogen growth altered by acidity?
Foods often have a high or low pH in order to limit microbial growth
Provides a way of preserving food
How is pathogen growth altered by water activity?
High water activity within foods leads to more rapid rancidity
Lowering water activity is a way of preserving foods
- Drying
- Concentrating
- Adding salt or sugar
How is pathogen growth altered by chemicals?
Antimicrobials
Sterilants
Disinfectants
What are antimicrobial agents?
Natural or synthetic chemicals that kill or inhibit growth of microbes
- cidal = kill microbes
- static = inhibit microbial growth
What are sterilants?
Destroy all forms of microbial life
What are disinfectants?
Kill microbial cells but do not always inactivate spores
