soil microbiology and microbial growth

Topics: Bacterial growth, Bacteria, Agar plate Pages: 18 (4870 words) Published: January 21, 2014

Microbiology and Process Analysis laboratory

Group 1

Microbiology laboratory

The lab exercises were divided into three different analysis; microscopy, soil microbiology and bacterial growth. The main aim of laboratory work with Escherichia coli and soil sample was to introduce students to bacterial growth in pure culture and soil microbial flora. The experiment of bacterial growth in pure culture using optical density measurement, plate count and DAPI direct count, showed that Plate Spread method was more precise to understand bacterial population growth tendency and counting generation time. During laboratory work with soil sample were determined relative number of bacteria, Actinomycetes and molds. Results showed, that more abundant specie in soil sample were Actinomycetes and least abundant – molds. Samples of bacterial DAPI, wastewater flocculum and lake water were studied with a microscope in order to identify E. coli, filaments and phytoplankton for further analysis. A total of 5.72 x 106 E. coli bacteria were determined of the microscopy filter giving the first point on a growth curve. The growth curve suggests the bacteria entering their stationary growth phase with a flattening curve. Water from two sewage treatment plants, Vik and Grødaland was analysed, with Grødaland water containing a large amount of filaments. Phytoplankton diversity was compared between Stokkavannet andHålandsvannet, with Stokkavannet being most diverse as expected. 

1. Introduction
1.1. Soil Microbiology and bacterial growth
The main purpose of this laboratory exercise was to study the growth of a bacterial population in pure culture using optical density measurement, plate counts using spread plate method. Also there were taken samples for direct counts that were carried out during the Microscopy laboratory exercise. Experiment with soil was done to determine the relative number of bacteria, actinomycetes, and molds and introduce students with the soil microbial flora. Bacterial growth is the division of one bacterium into two daughter cells in a process called binary fission. Providing no mutational event occurs the resulting daughter cells are genetically identical to the original cell. Hence, "local doubling" of the bacterial population occurs. Both daughter cells from the division do not necessarily survive. However, if the number surviving exceeds unity on average, the bacterial population undergoes exponential growth. The measurement of an exponential bacterial growth curve in batch culture was traditionally a part of the training of all microbiologists; the basic means requires bacterial enumeration (cell counting) by direct and individual (microscopic, flow cytometry), direct and bulk (biomass), indirect and individual (colony counting), or indirect and bulk (most probable number, turbidity, nutrient uptake) methods. Models reconcile theory with the measurements. 1

Figur 1.3.1 Standard bacterial growth curve.2

Ideally, in a so called exponential growth phase cells divide into two during even time lapses. For example if one cell can become two in 20 minutes then the 2 new cells again will require 20 minutes to become 4 cells. This means that in each 20 minutes the number of bacterial cells in the culture is doubled. This can be mathematically expressed like in Equation 1 where X is bacterial number, X0 is the initial bacterial number and n is the number of generations. Transforming the expression with a logarithmic function (Equation 2) we can calculate the number of generations during a period of time as in Equation 3.2

logX=logX_0+ n∙log2
n= (logX-logX_0)/log2

Conditions are never ideal for long time; bacterial growth is limited by several factors. After an exponential growth phase the population enters a stationary phase followed by a death phase in case the limiting conditions remain. The typical curve for the...

References: 2. Wikipedia: October 28, 2012, URL:
5. Google images from Virginia Polytechnic Institute (2012)
7. Donnenberg, M.S and Kaper, J.B.(1992) Enteropathogenic Escherichia coli. Infect. Immun. October 1992 vol. 60 no. 10 3953-3961.
8. University of Waikato (2012) Resolving power of microscopes, Link to article: [] .
9. Google images from Virginia Polytechnic Institute (2012) Link to image:
11. MET160 Lab notes, 2012.
12. Environmental Leverage (2011) What are filaments, Link to article: []
14. National Oceanic and Atmospheric Administration (NOAA) (2012) Phytoplankton are microscopic marine plants, Link to article:[
15. IVAR (2011) Regionale renseanlegg (NOR), Link to article: [
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