Population growth and environmental factors

What is the process of bacteria reproducing called?

binary fission

What is generation time (doubling time)?

The time it takes for the population to double through a round of binary fission

given unlimited nutrients and space, bacteria populations will grow ____

exponentially

What qualifies as a doubling event?

each new generation

What fold does each generation increase by?

2

The length of a generation = ?

growth rate of an organism

Describe the generation time of bacteria.

avg time=30-60 minutes but can be as short as 10 minutes and span days, weeks, and years

Why can’t bacterial populations maintain exponential growth rate?

run out of space and nutrients

poison themselves with waste products

list and draw out the stages in the normal growth curve

only counts if axes are included

lag phase, exponential phase, stationary phase, death phase

describe the lag phase

relatively flat growth

newly inoculated cells that are adjusting to the new environment, enlarging, and synthesizing things

preparing to divide but no dividing happens yet

lag time varies between species

Describe exponential growth (log) phase

growth curve increase exponentially

• max rate of cell division (replicating as fast as they can)

continues as long as adequate nutrients and favorable environment exists

using up nutrients/food while secreting waste products

Describe the stationary phase

growth and metabolism slow dramatically (can stop completely)

rate of death = rate of multiplication

what are stresses that cause growth arrest?

depleted nutrients and oxygen

excretion of organic acids and other biochemical pollutants into the growth medium

• poison themselves with waste products

What phase of the growth curve do some bacteria form endospores?

stationary phase

What phase are bacteria most susceptible to drugs in? What about most resistant?

exponential phase

stationary phase

Describe the death phase of the bacterial growth curve

the curve goes downwards

cells start to die at an exponential rate ]

• waste kills them

some cells survive, but most die, not much replicating

What are the medical implications of exponentially growing bacteria?

cells dividing but more susceptible to antimicrobial agents

What are the medical implications of stationary bacteria under stress? What in an extreme form of this?

leads to active stress responses that makes bacteria more resistant to antimicrobials

enospores/ cysts are an extreme form of this

What are the steps to generating a growth curve in the lab?

1) Inoculate sterile liquid medium

2) At regular intervals pipette a small known amount of volume onto a sterile agar plate

3) (analysis) the number of colonies taht grow on each plate is a good estimate of the number of living cells that were pipetted onto that plate

What is the original cell that formed a colony called?

CFU

What is a colony?

The point at which a cell population is large enough to form a visible mass

several of millions of cells

How can we calculate the total population of cells in the broth at a given time point? (from colonies on a plate)

population size = (volume in tube/ volume pipetted onto plate) x (# of colonies on plate)

If a tube contains 50 mL, 0.1 mL was pipetted onto a plate, and 2 colonies formed, how large was the cell population in the original tube?

(50mL/0.1mL) x 2 = 1000 cells

What is osmosis?

the movement of water from areas of lower solute concentration to areas with higher solute concentration

What is a hypertonic environment/solution?

when an environment has a higher concentration of salt than inside the cell

Describe plasmolysis

When water moves out of the cell and can cause it to collapse inwards

How are halotolerant cells able to grow in environments with salt?

create an isotonic environment by manufacturing their own solutes and balancing out the environment

Describe acidophile, neutrophile, and alkaliphile

acidophile: grows at pH 1-5.5, best growth ~3.3

neutrophile: grows at pH 5.5-8.5, best growth ~7

alkaliphile: grows at pH 7.5-11.5, best growth ~9.5

What do halotolerant bacteria import or synthesize?

compatible solutes that allow cells to retain water and prevent plasmolysis

What do you call bacteria that grow in really cold temperatures?

psychrophiles

What do you call bacteria that grow in normal temperatures?

mesophiles

What do you call bacteria that grow in high heat?

thermophiles

What do you call bacteria that grow in extremely high heat?

hyperthermophiles

Describe an obligate aerobe.

have to have high levels of oxygen

form next to areas with high oxygen concentration

Describe obligate anaerobes

oxygen is toxic to them, needs low levels of oxygen

grows in areas with low levels of oxygen only

Describe facultative anaerobes

can grow throughout but prefer areas with oxygen

describe aerotolerant anaerobes

pretty even throughout, presence of oxygen doesn’t affect them

describe microaerophilic

bacteria that needs oxygen, but too much kills them

What happens when O2 steals electrons from proteins inside cells?

it becomes a reactive oxygen species

describe a ROS

unstable and can damage proteins, lipids, and nucleic acids

How do cells deal with the harmful effects of O2?

they convert ROS into other compounds

What does superoxide dismutase break down?

superoxide radical

What does catalase and peroxidase break down?

hydrogen peroxide