Lecture 7: Bacterial Nutrition Flashcards
Autotrophy
don’t need organic carbon for energy or structural carbon
phototrophy
light
lithotrophy
inorganic non-carbonaceous material for energy
heterotrophy
use reduced organic carbon
- parasite/pathogen
- saprophyte
What are the major nutrients?
- carbon
- nitrogen
- sulfur
- phosphorus
Carbon
About 50% of cell mass is carbon
- Either derived from inorganic or organic sources
Nitrogen
Some bacteria fix nitrogen directly from the
atmosphere
Some use ammonia or organic nitrogen from
digested macromolecules
Nitrogen makes up about 15% of cell “dry weight”
Sulfur and phosphorus
Between them, sulfur and phosphorus make up
about 4% of cell dry weight
Essential in protein, DNA structure, ATP
Organic trace elements
Essential in synthesis of cofactors such as FAD, NAD, CoA
Examples of inorganic trace elements
magnesium, molybdenum, iron, copper, and zinc
- These are required for growth, but are usually present in tap water in sufficient quantities
What functions require certain inorganic trace elements?
many enzymatic functions
- These are required for growth, but are usually present in tap water in sufficient quantities
Oxygen
present in many, many forms
Water, Carbon Dioxide, Oxygen Gas
Reactive forms such as peroxide, hydroxyl radicals
molecular oxygen is…
an essential nutrient for some organisms, a deadly
poison for others
Bacterial use enzymes to detoxify various reactive oxygen forms-hydrogen peroxide, free radicals
Superoxide dismutase, Catalase
How do obligate aerobes respond to oxygen?
cannot grow well in the absence of oxygen
How do facultative anaerobes respond to oxygen?
grow using fermentation pathways in the absence of O2
How do microaerophiles respond to oxygen?
grow only in the presence of small concentrations of molecular oxygen
How do aerotolerants respond to oxygen?
anaerobes can survive in the presence of oxygen, but cannot grow
How do obligate anaerobes respond to oxygen?
are killed by oxygen radicals generated in cells in the presence of oxygen
Scarce nutrients must be scavenged from…
the environment
Passive and active mechanisms for nutrient uptake
- symport and antiport
- ATP-binding cassette
PTS System
- transport of glucose across membrane
- high energy PEP transfers Pi to glucose (group translocation)
- other sugars can be transported analogously
What is often the limiting nutrient in the environment?
phosphate
What is the limiting nutrient in culture?
can be anything
What is often the limiting nutrient in pathogens?
often iron
What methods have bacteria developed to obtain limiting nutrients?
- phosphatases
- siderophores
How to make laboratory cultures
- start with sterile medium, defined or undefined
- media may be solid (add agar) or liquid
- add an inoculum, either of pure bacteria from a single species or a mixture (ex: soil or blood)
- the microbes multiply in the medium as it is incubated and the result is a culture
Nutrient Broth
- Nutrient Broth
Peptone (protein digest) 5g
Beef extract 3g
NaCl 8g
Water 1L
Defined E. Coli Medium (simple)
Glucose 5g
Ammonium Phosphate, monobasic 1g
NaCl 5g
Magnesium Sulfate, hydrated 0.2g
Potassium phosphate, dibasic 1g
Water 1L
Aerobic Growth
- easier
- incubator for constant temperature
- medium composition tends to be less complicated
Anaerobic Growth
- needs airtight chamber or anaerobic hood
- obligate anaerobes are killed by exposure to O2
- Obligate anaerobes need a reducing agent to be added
Anaerobic Jars
Put plates in a sealed jar containing a special
salt packet
When the packet is
opened, water added, chemical reaction
occurs, generates CO2
and hydrogen gas
Palladium catalyst allows reaction of oxygen and hydrogen to form water
What organism grows in amadillos?
Mycobacterium leprae
What grows in mammalian cell tissue culture?
Obligate intracellular bacteria such as Chlamydiae and Rickettsiae can only be grown as parasites
Capnophiles
may desire high CO2 levels
Uses of general growth media
- used to produce large populations of bacteria for many purposes (research, industrial processes)
Uses of selective and differential media
used to identify and detect specific organisms from various environmental sources
- especially relevant in clinical or public health settings
Enrichment Culture
Attempts to find organisms with certain biological characteristics
May be ability to use a particular carbon, nitrogen, or energy source, or to withstand certain environmental stresses
A sample from soil might be incubated in the presence of DDT as the only source of
carbon, and only organisms capable of degrading this pesticide would grow
The organisms that grow could then be isolated
Isolation (pure culture)
When a sample is taken from the environment, it can be plated onto solid
media, where isolated colonies will grow
Repeatedly using this procedure, isolates
can be obtained from even very dense cultures containing many species
Streak plate method
Culture preservation
- Agar plates will sustain a bacterial culture in the refrigerator for at most ~6 months
- freeze-drying (lyophilization)
- freeze at -80C with 15% glycerol to prevent ice crystals from destroying the cells
Slide 7 (left to right)
- Obligate anaerobe?
- aerotolerant?
- microaerophile?
- obligate aerobe?
