Micro Exam 2

Essential Nutrients

those that must be supplied (macronutrients and micronutrients)

Macronutrients

required in large quantities

• major elements in cell macromolecules

• - C,O,H,N,P,S

• Ions necessary for protein function

• - Mg2+, Ca2+, Fe2+, K

Macronutrients

required in small quantities

• Trace elements necessary for enzyme function

• - Co,Cu,Mn,Zn,Mo,Ni

All of Earth’s life forms are based on ____, which they acquire in different ways

carbon

Heterotrophs

Use preformed organic molecules

• release CO2

Autotrophs

fix CO2 and assemble into organic molecules (mainly sugars)

• phototrophy: use light energy

• Lithotrophy: energy from the oxidation of minerals

2 ways of transportation across a membrane

Passive transport: does not require energy

• simple and facilitated

Active transport: requires energy

• coupled transport

• ABC transporters

Facilitated diffusion

Helps solutes move across a membrane from a region of high concentration to one of lower concentration

• it does not use energy

• Ex: Aquaporin family transports water and small polar molecules such as glycerol

Active transport requires E:

• Coupled transport systems

moving a driving ion down its gradient used to move a solute up its gradient

• symport: the two molecules travel in the same direction

• antiport: the actively transported molecule moves in the direction opposite to the driving ion

Active transport requires E:

• ATP-binding cassette superfamily-ABC transporters

They are found in all 3 domains of life

• uptake ABC transporters: transport nutrients

• Efflux ABC transporters: multidrug efflux pumps (multi-drug resistance)

Aptake ABC transporters

1. solute binds to binding protein, and the complex then binds to the membrane transporter (green)

2. The ATPase activity of one component (yellow) powers the opening of the channel (green) and;

3. movement of the solute into the cell

Growth Cycle

Most bacteria divide by binary fission, where one parent cell splits into two equal daughter cells

• however, some divide asymmetrically (Hyphomicrobium divides by budding)

• others split into more than two cells

Exponential Growth

• The growth rate, or rate of increase in cell numbers or biomass, is proportional to the population size at a given time

• Such growth rate is called “exponential” because it generates an exponential curve

• if a cell divides by binary fission, the number of cells is proportional to 2^n (n=the number of generation)

Microbial growth cycle

• exponential growth never lasts indefinitely

• resources are always the limiting factor for growth

• Bach culture: a liquid medium within a closed system

• The changing conditions in this system greatly affect bacterial physiology and growth - this illustrates the remarkable ability of bacteria to adapt to their environment

continuous culture

all cells in a population achieve a steady state, which allows detailed study of bacterial physiology

• the chemostat ensures logarithmic growth by constantly adding and removing equal amounts of culture media

• note that the human gastrointestinal tract is engineered much like a chemostat

Generation time

the time it takes for a population to double

Microbes in nature exist in complex, multispecies communities, but for detailed studies, how must they be grown?

separately in a pure culture

What are the 2 types of culture media?

1. liquid or broth: useful for studying the growth characteristics of a pure culture

2. Solid (gelled with agar): useful to separate mixed cultures

Complex media

nutrient rich but poorly defined

synthetic media

precisely defined

Enriched media

complex media to which specific blood components are added

• fastidious: requiring blood (like vampire)

selective and differential media

• selective favor the growth of one organism over another

• Differential exploit differences between 2 species that grow equally well

example of differential media

E. coli vs. Salmonella

• Lactose

• Peptones

• Neutral red indicator

• Red - Acid

What are 2 main techniques to isolate pure colonies?

1. streaking an agar plate

• dragging a loop across the surface of an agar plate (incubate for 24 hours)

2. Spread plate

• serial dilutions are performed on a liquid culture

• a small amount of each dilution is then plated

• plate with isolated colonies is used

• used to count colonies

Why is it important to know the number of organisms in a sample

• to determine infectious dose

• actual infection vs contamination of specimens

direct microscopic count

counted on a special microscope slide, called a counting chamber

Fluorescence-Activated Cell Sorter (FACS)

• fluorescent cells are passed through a small opening and then past a laser

• Detectors measure light scatter

• measure particle size and shape

Viable cell count

count replicating and colony forming cells

1. pour plate method

2. optical density (spectrophotometer) - the fastest way to measure cell density

Pour plate method

• Tenfold serial dilutions are performed on a liquid culture

• a small amount of each dilution is then plated

• A plate with 30-300 colony forming units is counted

The growth cycle of organisms grown in a liquid batch culture consists of what 4 phases?

Lag, log, stationary, death