Environmental Factors Affecting Growth of Bacteria

The purpose of this experiment is to determine optimal conditions for kinds of bacteria by using E.coli and G.vulcani according to temperature, pH and different NaCI concentrations.
Every living organism needs some optimal conditions to grow, reproduction etc. These conditions can be changed by chemical or physical events. In biological applications, bacterial growth can be controlled by these conditions. Rate of growth can be increased or decreased or made stabile. In microbiology, two basic aspects exist, characterization and control. (1)
Firstly optimal conditions of organisms are obtained. It means best physical or chemical conditions that give highest rate of growth. After obtaining optimal conditions, bacterium has been characterized. After that, lethal limits are determined by researchers. It means that conditions kill bacterial population. Each kind of bacteria has these limits. These environmental limits are used for aseptic techniques and also minimum lethal conditions can help to kill pathogenic bacteria. (1)
Temperature, oxygen and hydrogen ion concentrations (pH) are basic conditions for testing. Additionally nutrients may be important for bacterial growth.
Effects of temperature:
Every organism have enzyme that works at between a certain temperature ranges. Evolutionary conditions caused these ranges. Optimum temperature is a term to define best temperature for bacterial growth. Bacteria can be specially named according to optimal temperature range. (2)
Psychrophiles: between -10° C and 20° C
Psychrotolerants: between 5° C and 30° C
Mesophiles: between 10° C and 47° C
Thermophiles: between 40 ° C and 75° C Hyperthermophiles: at 65 ° C to 120° C
Effect of pH or Hydrogen ion concentration:
Like temperature, enzymes needs suit pH range to work well. Environmental conditions have different pH or Hydrogen ion concentration. Best pH value for a kind of bacteria is called optimum pH. Many of bacteria live in natural pH range, but some bacteria have evolved to acidic environment and they are called acidophilic ones or some of them have evolved for higher pH values and they are called as alkaliphilic microorganisms. Hydrogen ion concentration is also depended on other conditions like temperature, nutrients. These also can change concentration and affect pH value.
Osmatic pressure:
Concentration difference can form a pressure between environment and inside of cell. This is osmotic pressure. Environment that has higher or lower concentrations than inner side of cell caused that some bacteria improve their survival skill to live these types of places to not be plasmolyzed. Some of bacteria live in different concentrated environment. Halophiles are one of these kinds of organisms. They live in minimum concentration of salt. Obligate halophiles need %13 salt concentration. As to osmophiles, their living environment is high concentrated organic solute such as sugar.(4)

Material and Methods:
Effects of Temperature,
E.coli and G.vulcani cultures
Bunsen burner
Incubator, water bath, refrigerator
The tube was labelled according to temperature values and kind of bacteria before experiment. Prepared bacteria samples were transmitted into the tubes with aseptic techniques and then the tubes with bacteria was placed to incubators, water or refrigerator according to interested temperature value (40C, 20-250C , 370C, 420C, 550C, 620C, 700C). Next day, the samples was observed and recorded on the tables by comparing each other.
Effects of pH,
E.coli culture
LB broth with different pH values
Bunsen burner
The bacterial samples were transmitted into the LB tubes that are different pH. The samples in LB tubes were waited into incubator at 370C for overnight. Next day, the samples were observed and recorded to table.
Effects of Osmotic Pressure,
E.coli culture
LB agar plates including several concentrations of salt (NaCl)Spreader
Bunsen burner
100 µl of bacterial samples were inoculated to agar plates that include NaCI concentration in certain ratios (0.5, 1, 5, 10 and 20). Next day, the plates were observed.
Bacteria Culture
Temperature Growth of E.coli (Broth) Growth of G.vulcani
40C – –
20-250C (room temperature) + –
370C + –
420C ++ +
550C – ++
620C – +++
700C – +++

pH Bacteria Growth of E.coli (LB Broth)
3 –
4 –
5 +
6 ++
7 ++
8 +
9 +
10 –

NaCI(%) Growth of E.coli (LB Broth)
0 ++
0,5 ++
5 +++
10 –
20 –
The aim of the experiment was to obtain optimal conditions and lethal limits of bacteria according to temperature, pH and salt concentration.
At first step, effect of temperature was examined on bacteria. With different degrees of temperature, bacterial (E.coli and G.vulcani) samples were tested. E.coli is a mesophilic bacterium. As optimal temperature, 370C is best for E.coli growth. Experimental data (Table 1.1 and Graph 1.2) confirm expectations and theoretical information. Observations show that E.coli bacteria grow easily between room temperature and 420C. On the other hand, G.vulcani likes hotter environment according to data (Table 1.1 and Graph 1.2). After 420C, there is an increasing at rate of growth and as maximum 62-700C can be optimum for G.vulcani. Higher temperatures can be added to optimum for G.vulcani.
At second step, pH was examined as range for only E.coli. After observing results, E.coli can live in more neural pH value (Table 2.1 and Graph 2.2). E.coli culture started to grow at between 3 and 9, but as optimum pH value the best pH values are 6 and 7. It shows that enzyme activity of E.coli is highest at 6 and 7
Lastly, salt concentration is used for E.coli. E.coli is known as a bacterium living at normal conditions for temperature, pH and osmatic environment. Table 3.1 and Graph 3.2 show that E.coli can live at high salt concentration and it also indicates that E.coli doesn’t have any evolutionary mechanism for osmatic pressure. Cells cannot resist and overcome from this pressure. For better transport from out and inside of cell membrane, a certain concentration difference is also good for cells. For E.coli cells, this range is until 5%. 5% slat concentration can give a good environment for nutrient transport for cells (Table 3.1 and Graph 3.2).
[1] Koch AL (2002). “Control of the bacterial cell cycle by cytoplasmic growth”. Crit Rev Microbiol. 28 (1): 61–77.
[2] Daniel RM, Peterson ME, Danson MJ, et al. (January 2010). “The molecular basis of the effect of temperature on enzyme activity”. Biochem. J. 425 (2): 353–60. .
[3] (http://www.biologyreference.com/Dn-Ep/Enzymes.html)
[4] Madigan, Michael T., and Barry L. Narrs, “Extremophiles” Scientific American, April 1997: 82-88

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