The Effect of Environmental Factors Such as Temperature, Osmotic Pressure, Oxygen Concentration and Ph on Microbial Growth and Survival

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The effect of environmental factors such as temperature, osmotic pressure, oxygen concentration and pH on microbial growth and survival

Microbial growth can be affected by different environmental factors such as temperature, osmotic pressure, oxygen concentration and pH. Six experiments were carried out in this report testing for microbial growth against different environmental factors. Good aseptic techniques were used to prevent contamination, resulting in a uniform set of results that are in line with the literature.

Bacteria vary greatly in terms of their characteristics and morphology. Colonies can be classified according to their colour, form, elevation, margin and size. Pure cultures of microorganisms
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The colonies of M. Luteus were yellow in colour, circular colonies which are convex with entire margins.

Experiment 2: Selective and differential plating
Table 1: The size, sheen and colour of the colonies of the organisms on the EMB plate E. coli E. aerogenes B. subtilis
Size Small Small No growth
Sheen Green sheen No green sheen -
Colour Black Purple/pink -

Experiment 3: Effect of temperature on bacterial growth
Table 2: Microbial growth of the cultures incubated at varying temperatures (+ growth, - no growth) Growth of cultures
Slant Temperature (oC) E.coli P.fluorescens B.stearothermophilus
1 -4 - + -
2 25 + + +
3 37 + - +
4 65 - - +
5 85 - - -

Experiment 4: Effect of environmental factors on microbial growth – osmotic pressure
Table 3: Microbial growth of cultures on nutrient agar plate with varying salt concentration (+ growth, - no growth)

% Salt E. coli M. luteus V. natriegens
0.5 + + +
5 - - +
6.5 - - +
10 - - +

Experiment 5: Effect of oxygen concentration on bacterial growth
Table 4: Amount of microbial growth present in the molten agar previously boiled to drive off oxygen when 0.5ml of each bacterium was inoculated.

Inoculated bacterium Growth
E. coli Scattered growth at the top and throughout
C. sporogenes Scattered growth at the bottom
B. subtilis Growth at the top

Experiment 6: Effect of environmental factors on microbial growth – pH

Table 5: Microbial growth of salin cultures at