Announcements

• Seminar today at 12 PM– You must attend at least 10

• Review session tomorrow at 4 PM for the exam-Ellison 202– Bring questions, muddiest points

• Using the microscope tutorial Wednesday…time?• No lab this week or online quiz• Exam on Thursday: Chapters 1-4

**Bring calculator with log function**

Chapter 4: Dynamics of Prokaryotic Growth

2 Minute Brainstorm and RecapThink back to the structure of a prokaryotic cell…

What parts of the bacteria cell must be doubled prior to replication?

How Bacterial Cells Divide?

• http://www.hhmi.org/biointeractive/bacterial-growth

• Binary Fission:

Case Study: Should I Eat That?• It was supposed to be a fun Saturday. Since college

classes are in full swing, you decided to take a break from studying to go with friends to an outdoor picnic.

• Hamburgers were grilled. However, you weren’t hungry. You decided to play football and hang out with friends to work up an appetite.

• About 3 hours later, you’re hungry and think about eating the hamburger left out on the picnic table in the sun. But you think to the local news report you saw on TV saying E. coli was found in ground beef and 10-100 of them cause food poisoning.

Your Task: Should I Eat The Hamburger? • You decide to quickly apply your knowledge

from your Microbiology class to determine whether the hamburger is safe to eat 3 hours after it was cooked.

• You ask yourself how many bacteria are in the hamburger at 3 hours? And that will determine if it is safe to eat!

Exponential Bacteria Growth• Refers to microbial growth or the increase in the number of cells in

a given population (not size of a bacterium)

• Generation time: time it takes a population to double

• Nt = N0 x 2n

• Nt= number of bacteria cells at given

time• N0= number of cells in starting population• n= number of divisions undergone during

that time: total time elapsed (t) generation time (g)

Your Task: Should I Eat The Hamburger?

• You assumed the hamburger had 1 E. coli. after it was cooked.

• You Googled the generation time (g) for E. coli: 20 mins

• How many bacteria were there 3 hours later?• First thing to know, how many divisions (or

generations) have the bacteria undergone in 3 hours: n=t/g?

Nt = 1 x 29

Nt = 1 x 512 Nt = 512 bacteria

9

Question: Homework

What is the generation time of a bacterial population that increases from

30,000 cells to 30,000,000 cells in 5 hours of growth?

Look at HINT on handout!

How Do Bacteria Grow? • Bacteria grow ONLY when environment is suitable:– Need a continuous supply of nutrients (open system)

• In the lab, we have determined the stages of growth of bacteria– (closed system)

Introduce a small # of bacteria to sterile broth to grow (inoculate)

Phase 1: Lag phase- cells begin synthesizing enzymes required for growth*Cells are not dividing yet, so the number of bacteria remains ~constant

How Do Bacteria Grow?

Phase 2: Log phase- cells divide at a constant rate; most growth occurs at this stage (increase in numbers)

*Most important stage for treating infections with antibiotics

**Most important stage for collecting bacterial products (called primary metabolites) such as amino acids sold as supplements

Phase 3: Stationary phase -number of living cells stays relatively constant as the level of nutrients declines and waste products increase

How Do Bacteria Grow?

Stationary phase is entered when nutrient levels are too low to sustain growth.

Some cells dividing some cells multiplying. How?Living off the dead cell

X X

Phase 4: Death phase -number of living cells decreases as cells die off at a constant rate (exponential, but slower than log phase growth rate)

How Do Bacteria Grow?

Phase 5: Prolonged decline phase – a fraction of the population survives the death phase and have adapted to the worsened conditions; can multiple a little bit using nutrients from dead cells (very slow decline)

“Survival of the fittest”- newly divided bacteria are better adapted to survive in the harsh conditions (very few nutrients available)

How Do Bacteria Grow?

What factors influence bacterial growth?

http://www.foodsafetyfirst.org/fsf_mgsp.html

Environmental Factors Influence Bacterial Growth

• Temperature

• Oxygen (absence or presence)

• pH

• Water

Some like it hot, others do not…

Body temperature:37C

Refrigerator4C

Room temp:25C

Boiling:100C

Why do we refrigerate our food?• Refrigerator temperature: 4oC• Slow the growth of fast growing mesophiles

Refrigerator4C

Why does food spoil

then?

Extremophiles (Extreme microbes)

• Psychrophiles: grow in the cold Arctic and Antarctic regions in lakes that receive runoff from glaciers

• Thermophiles: grow in hot springs

Blood Falls in Antarctica

Morning Glory Hot Springs, Yellowstone

Environmental Factors Influence Bacterial Growth

• Temperature

• Oxygen (absence or presence)

• pH

• Water

Oxygen Requirements: 5 groups

• Obligate aerobe- absolutely requires O2 for aerobic respiration

• Facultative anaerobe- grow better if O2 is available but can grow without it

• Microaerophiles- need small amounts of O2 (2-10%) for aerobic respiration; high amounts are toxic

• Aerotolerant anaerobes- do not care if O2 is around; grow in it, grow without it

• Obligate anaerobe- cannot grow in the presence of O2(air is toxic)

Oxygen

NoOxygen

How do you determine a bacteria’s oxygen requirement?

Then look at growth!

Match the group of bacteria to the growth in oxygen

A. Obligate anaerobe

B. Obligate aerobeC. Aerotolerant

anaerobeD. Facultative

anaerobeE. Microaerophile

AB CED

Reactive Oxygen Species (ROS)

ROS can damage cell components (looking to fill their outer shell with electrons)Bacteria that use oxygen must use mechanisms to protect from ROS: Superoxide dismutase- inactivates superoxide by converting it to O2 and H202

Catalase- converts H2O2 to O2 and water (*catalase test)

Environmental Factors Influence Bacterial Growth

• Temperature

• Oxygen (absence or presence)

• pH

• Water

Most Microbes Survive at Neutral pH

--------------------------------------

Stomach Acid pH 1-2

How does Helicobacter survive?

Most Microbes Survive at Neutral pH…Even If They Have to Create It

--------------------------------------

Stomach Acid pH 1-2

Ammonia (basic) Neutralizes Acidic pH

Is Pickling Just For Taste?

• No, it lowers the pH to 4.6• Inhibits bacteria growth ----------------------------------

Pickling

Environmental Factors Influence Bacterial Growth

• Temperature

• Oxygen (absence or presence)

• pH

• Water

Sugar, Salt, and Water…Oh My!• All microorganisms require water for growth• Salts and sugars interact with water molecules

and make them unavailable to microbes

Some Bacteria Love Salt Like Us!

• Some microbes can tolerate high salt concentrations (up to 10%; halotolerant)

• Example: Staphylococcus species live on the dry, salty surface of your skin

• Halophiles- require high salt levels to live• Example: ocean organisms and those living in Utah salt flats

Is Salt or Sugar Curing Just For Taste?

• No, salt and sugar prevent bacteria from growing by binding up the available water

• Do the bacteria shrink up or swell/explode?

Hypertonic conditions = Plasmolysis