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Lecture 6: Quantifying MicroorganismsCEE 210 Environmental Biology for Engineers

Instructor: L.R. Chevalier

Department of Civil and Environmental Engineering

Southern Illinois University Carbondale

Objectives

Review the composition of microorganisms

Calculated the THOD of bacterial cells

Understand the bacterial growth curve

Calculate the specific growth rate of bacteria

Review methods for measuring bacteria

Chemical Formula of Microorganisms

Other elements include, but are not limited to, phosphorus, sulfur, potassium, calcium and magnesium

- Most commonly used
- C5H7O2N
- Useful simplification, but not a true chemical formula nor an exact stoichiometric expression
- Compare these values to the elemental composition of E. coli

Chemical Formula of Microorganisms

- C5H7O2N
- We can use this formula
- Estimate nutrient requirements
- Convert gravimetric cell mass measurements into THOD of cell tissue
- Consider the following example that determines the THOD of microbial cells

Example: THOD of Bacterial Cells

Determine the theoretical oxygen demand of 1 g of microbial cells using the empirical formula for microbes. Assume that the organic nitrogen in the cells is not oxidized (remains in the -3 oxidation state).

Bacterial Growth

Source: Stanier et al., 1986

- Binary fission
- 20, 21,22,23…..2n where n is the number of generations
- Generation time a.k.a. Doubling time
- Time it takes for two cells to form from the parent cell
- It is also the time it takes to double the cell numbers
- This varies by species and growth conditions

Exponential Growth

N = number of cells per volume of medium

t=time

k=specific growth rate

No = number of cells per volume when t=0

td = doubling time

Bacterial Growth Curve

- Exponential growth can only be carried out up to a certain point
- Limited by environmental conditions, e.g. nutrients depleted
- Closed batch systems consistently show a bacterial growth with 4 distinct phases
- Lag phase
- Exponential growth phase
- Stationary phase
- Death phase

Bacterial Growth Curve

- lag phase
- Microorganisms initially adjust to the new environment
- Indicative of microbe’s ability to degrade waste
- exponential phase
- Microorganisms start dividing regularly by the process of binary fission
- stationary phase
- Exhaustion of available nutrients
- Limited oxygen
- pH changes due to build up of CO2
- Accumulation of end products;
- Limited space
- death phase
- Number of viable cells decreases geometrically (exponentially), essentially the reverse of growth during the exponential phase
- N=Noe-bt

Example of Exponential Growth

Given the bacterial cell numbers in a batch reactor measure 34,000/L in 4 hours after incubation, and 5.2 x 106/L after 24 hours. Assuming a negligible lag phase, estimate:

The specific growth rate

The initial number of cells

Objectives

Review the composition of microorganisms

Calculated the THOD of bacterial cells

Understand the bacterial growth curve

Calculate the specific growth rate of bacteria

Review methods for measuring bacteria

References

Chapter 11: Quantifying microorganisms and their activity

Bioremediation Principles, 1998, Ewies, J.B., Ergas, S.J., Chang, D.P.Y., Schroeder, E.D., WCB McGraw Hill.

Todar’s Online Textbook of Bacteriology, K. Todar, http://www.textbookofbacteriology.net/index.html (accessed March 2010)

Stanier, R.Y. et al., 1986, The Microbial World, Prentice-Hall.

Sources of photographs and images in sidebar

About the Instructor

- Professor, Civil and Environmental Engineering
- Fellow, American Society of Civil Engineers (ASCE)
- Diplomat, Water Resources Engineering, American Academy of Water Resources Engineering (AAWRE)
- Board Certified Environmental Engineer, American Academy of Environmental Engineers (AAEE)
- Licensed Professional Engineer, State of Illinois

- Human brain
- http://www.healthnak.com/mind/
- X-rays images
- http://martingallerycharleston.com/index.html
- Cold Virus (altered in Photoshop)
- http://medphoto.wellcome.ac.uk/

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