Chapter 6

Microbial Nutrition and

Growth

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 2MDufilho

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 3MDufilho

Growth Requirements

• Associations– Organisms live in association with different species

– Antagonistic relationships– Synergistic relationships– Symbiotic relationships

7/6/11 4MDufilho

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 5MDufilho

Figure 6.17 Binary fission events-overview

7/6/11 6MDufilho

Growth of Microbial Populations

ANIMATION Binary Fission

7/6/11 7MDufilho

Figure 6.18 Comparison of arithmetic and logarithmic growth-overview

7/6/11 8MDufilho

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 9MDufilho

Figure 6.19 Two growth curves of logarithmic growth-overview

7/6/11 10MDufilho

Figure 6.20 Typical microbial growth curve

Stationary phase

Death(decline)phaseLog

(exponential)phase

Lag phase

Time

Nu

mb

er

of

live

ce

lls (

log

)

7/6/11 11MDufilho

Figure 6.21 Schematic of chemostat

Fresh medium witha limiting amountof a nutrient

Sterile airof othergas

Culture

Culturevessel

Flow-rateregulator

Overflowtube

7/6/11 12MDufilho

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 13MDufilho

Figure 6.22 Estimating microbial population size-overview

7/6/11 14MDufilho

Figure 6.23 Use of membrane filtration to estimate microbial population-overview

7/6/11 15MDufilho

Figure 6.24 The most probable number (MPN) method for estimating microbial numbers

1.0 ml 1.0 ml

1:1001:10Undiluted

Inoculate 1.0 ml intoeach of 5 tubes

Phenol red, pHcolor indicator,added

Incubate

Results

4 tubes positive 2 tubes positive 1 tube positive7/6/11 16MDufilho

Figure 6.25 The use of a cell counter for estimating microbial numbers-overview

7/6/11 17MDufilho

Growth of Microbial Populations

• Measuring Microbial Growth– Indirect methods

– Metabolic activity– Dry weight– Turbidity

7/6/11 18MDufilho

Figure 6.26 Spectrophotometry-overview

7/6/11 19MDufilho

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 20MDufilho

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 21MDufilho