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 Recap Think back to the structure of a prokaryotic cell… What parts of the bacteria cell must be doubled prior to replication? Figure 3.23
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? How would you solve for 9 Nt = 1 x 29 Nt = 1 x 512 Nt = 512 bacteria
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? *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 2: Log phase- cells divide at a constant rate; most growth occurs at this stage (increase in numbers)
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 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? 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? “Survival of the fittest”- newly divided bacteria are better adapted to survive in the harsh conditions (very few nutrients available) 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)
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… Refrigerator 4C Room temp: 25C Body temperature: 37C Boiling: 100C
Why do we refrigerate our food? Refrigerator temperature: 4oC Slow the growth of fast growing mesophiles Refrigerator 4C 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 No Oxygen
How do you determine a bacteria’s oxygen requirement? Then look at growth!
Match the group of bacteria to the growth in oxygen D E C Obligate anaerobe Obligate aerobe Aerotolerant anaerobe Facultative anaerobe Microaerophile
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 How does Helicobacter survive? Stomach Acid pH 1-2 --------------------------------------
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