Chapter 6: Microbial Growth

August 15, 2013

Requirements for Growth

•There are two ways to microbial growth can be divided

• Physical

•Chemical

Physical Requirements•Temperature

• Hyperthermophiles –some members of Archaea, “extreme thermophiles”

• Psychrophile-cold loving microbes

•Mesophile-moderate temperatures (most common)

• Thermophile-heat loving microbes

• Psychrotrophs-capable of growing between 0 and 30 degrees Celsius (refrigerator temperatures)

•pH – the acidity or basicity of a solution

•Most bacteria growth best at a pH between 6.5-7.5

• Neutral

•Osmotic pressure

•Microbes are 80-90% water

•Adding solutes to solutions can reduce the presence of microbes (i.e. salt)

Chemical Requirements

• Carbon

• Carbon is the structural backbone of all living matter

• Organic compounds

• Nitrogen, Sulfur, Phosphorus

• N2 and P required for synthesis of DNA and ATP

• N2 required for protein synthesis

• Trace Elements

• Needed for enzymatic functions

• Can be added to media to culture microbes

• Fe, Cu, Zn

•Oxygen

•Obligate Aerobes- require O2 to live

•Facultative Anaerobes – can use O2 to live if present, but doesn’t require it for growth

•Obligate Anaerobes – do NOT require O2 to live, harmed by it

•Aerotolerant Aerobes- can not use O2 for growth, but they can handle it. Not necessarily harmed by the presence of O2

Chapter 6 Continued

Microbial Growth

Page 166 in your Textbook

CULTURE MEDIA•There are many different mediums that microbes can grow in

• Some require specific requirements, whereas others are more universal

•Culture Medium: a nutrient material prepared for the growth of microorganisms in a laboratory

•To introduce microbes to a media, you have to inoculate them

• This is what we did when we swabbed for microbes and put them on the agar.

• If bacteria grows and multiplies on the media, it is referred to as a culture.

•A complex polysaccharide derived from a marine algae is called agar.

Types of Media•Chemically defined medium = the exact

chemical composition is known

•Complex media = a media that is made of nutrients, chemical composition varies from plate to plate; includes yeast, plant and meat extracts

• Nutrient broth or nutrient agar

•Reducing Media = anaerobic conditions and stored in anaerobic jars to remove any oxygen

•Selective Media = Media used to encourage growth of some organisms while suppressing the growth of others

•Differential Media = Media used to distinguish colonies of specific bacteria from other organisms

•Enrichment Culture = media that mimics environmental conditions that favor the growth of a particular microbe but not another

Obtaining Pure Cultures•The most commonly used method to get pure cultures is the streak plate method

Growth of Bacterial Cultures •Bacterial cells divide by

binary fission, some by budding

• The time for a cell to divide is called generation time

• 1-3 hours is typical for most bacteria

• E.coli reproduces every 20 minutes!

Calculating Generation Time

(Initial # of cells )X (2 number of generations )= # of cells

•Example: A Taco Bell manager accidentally inoculated 5 cells of E. coli into the burrito meat. How many cells would there be after 4 hours if E.coli has a generation time of 20 minutes.

Phases of Growth•A bacterial

growth curve shows the growth of cells over time

• LAG PHASE

• EXPONENTIAL PHASE

• STATIONARY PHASE

• DEATH PHASE

REVIEW CHAPTER 6•PAGE 185-186

•Review #’s: 2, 4, 10, 12

•Multiple Choice #’s: 8, 9

•Describe physical and chemical requirements for growth

• Label these test tubes with the type of oxygen-organism

GROUP TEACH• Page 178-read first 2

paragraphs

• PLATE COUNTS-dilutions

• FILTRATION

• MPN

• DIRECT MICROSCOPE COUNT

Each group tell me:• Tell the method of

measuring cell growth

• Advantages/Disadvantages

•When is it used

•What is the process

• Picture or Diagram