Presentation on theme: "**Microbial Growth** Growth= an increase in the number of cells, not an increase in size Generation=growth by binary fission Generation time=time it takes."— Presentation transcript:
1 **Microbial Growth**Growth= an increase in the number of cells, not an increase in sizeGeneration=growth by binary fissionGeneration time=time it takes for a cell to divide and the population to double
3 Generation times vary for each organism E. coliMycobacterium tuberculosis
4 **Bacterial growth curve** Know the phases of the bacterial growth curve what the X and Y axes represent. Be able to explain why the curve is shaped the way it is – i.e., what is happening in each of the phases and how that relates to bacterial growth. Also know the changes in production of primary and secondary metabolites at different stages in the growth curve.
5 *Primary and Secondary metabolites I will ask you about secondary metabolites – know what they are, when they are produced and why.
6 **Requirements for bacterial growth** Environmental factors that influenceTemperature, pH, osmotic pressure, oxygenNutritional factorsCarbon, nitrogen, sulfur, and phosphorousTrace elements
7 *Optimum Growth Temperatures Psychrophiles-optimum -5 to 15oCPsychrotrophs- range from 20-30oCMesophiles- range from 25-45oCThermophiles-range from 45-70oC
11 **Oxygen preferences of organisms** Obligate aerobes require oxygen for growthFacultative anaerobes: can grow in aerobic or anaerobic environmentsObligate anaerobes: unable to grow in the presence of oxygen
12 **Why can some organisms grow in the presence of oxygen?** Because they have the ability to neutralize toxic oxygen molecules (superoxide, oxygen radicals)Toxic forms of oxygen need to be neutralized by enzymesSuperoxide dismutaseCatalase
14 Candle jars increase CO2 levels for growing capnophiles How does a candle jar create a CO2-enriched/O2-depleted environment? Is it an anaerobic environment?
15 Anaerobic jars eliminate the oxygen for anaerobes to grow. How does the hydrogen gas generator create an anaerobic environment?
16 Chemical requirements: Carbon What are possible sources of carbon?Bacteria are classified based on the source of carbon as either heterotrophs or autotrophs
17 Classification based on Energy and Carbon sources
18 Chemical Requirements: Nitrogen Why do bacteria need nitrogen?
19 Chemical requirements: Sulfur and Phosphorous Why do bacteria need sulfur?Why do bacteria need phosphorous?
20 Chemical requirements: trace elements Small amounts of mineralsUsually function as cofactors
21 *Culture Media Chemically defined GSA A chemically defined medium is one where we know EXACTLY what the ingredients are. An undefined medium is one where we don’t know the exact chemical makeup (for instance, it may contain “protein digest”