Microbial Nutrition and Growth Chapter 6 Microbial Nutrition and Growth

Result of microbial growth is discrete colony Growth Requirements Microbial growth Increase in a population of microbes Result of microbial growth is discrete colony An aggregation of cells arising from single parent cell Reproduction results in growth 7/6/11 MDufilho 2

Microbes obtain nutrients from variety of sources Growth Requirements Organisms use a variety of nutrients for their energy needs and to build organic molecules and cellular structures Most common nutrients contain necessary elements such as carbon, oxygen, nitrogen, and hydrogen Microbes obtain nutrients from variety of sources 7/6/11 MDufilho 3

Growth Requirements Associations Organisms live in association with different species Antagonistic relationships Synergistic relationships Symbiotic relationships 7/6/11 MDufilho 4

Growth Requirements Biofilms Complex relationships among numerous microorganisms Develop an extracellular matrix Adheres cells to one another Allows attachment to a substrate Sequesters nutrients May protect individuals in the biofilm Form on surfaces often as a result of quorum sensing Many microorganisms more harmful as part of a biofilm 7/6/11 MDufilho 5

Figure 6.17 Binary fission events-overview 7/6/11 MDufilho

Growth of Microbial Populations ANIMATION Binary Fission 7/6/11 MDufilho 7

Figure 6.18 Comparison of arithmetic and logarithmic growth-overview 7/6/11 MDufilho

Growth of Microbial Populations Generation Time Time required for a bacterial cell to grow and divide Dependent on chemical and physical conditions 7/6/11 MDufilho 9

Figure 6.19 Two growth curves of logarithmic growth-overview 7/6/11 MDufilho

Figure 6.20 Typical microbial growth curve Stationary phase Death (decline) phase Log (exponential) phase Number of live cells (log) Lag phase Time 7/6/11 MDufilho

Figure 6.21 Schematic of chemostat Fresh medium with a limiting amount of a nutrient Flow-rate regulator Sterile air of other gas Culture vessel Culture Overflow tube 7/6/11 MDufilho

Growth of Microbial Populations Measuring Microbial Reproduction Direct methods Serial dilution and viable plate counts Membrane filtration Most probable number Microscopic counts Electronic counters 7/6/11 MDufilho 13

Figure 6.22 Estimating microbial population size-overview 7/6/11 MDufilho

Figure 6.23 Use of membrane filtration to estimate microbial population-overview 7/6/11 MDufilho

Inoculate 1.0 ml into each of 5 tubes Figure 6.24 The most probable number (MPN) method for estimating microbial numbers 1.0 ml 1.0 ml Undiluted 1:10 1:100 Inoculate 1.0 ml into each of 5 tubes Phenol red, pH color indicator, added Incubate Results 7/6/11 MDufilho 4 tubes positive 2 tubes positive 1 tube positive

Figure 6.25 The use of a cell counter for estimating microbial numbers-overview 7/6/11 MDufilho

Growth of Microbial Populations Measuring Microbial Growth Indirect methods Metabolic activity Dry weight Turbidity 7/6/11 MDufilho 18

Figure 6.26 Spectrophotometry-overview 7/6/11 MDufilho

Growth of Microbial Populations Measuring Microbial Reproduction Genetic methods Isolate DNA sequences of unculturable prokaryotes Used to estimate the number of these microbes 7/6/11 MDufilho 20

Case Study–Can a trip to the dentist be life threatening? Details of the case Why do we get our teeth cleaned? Why does Betty feel so bad? What has happened? Will the biofilm return? How did they figure out Betty had septicemia? 7/6/11 MDufilho 21