Microbial growth Microbial growth indicates “an increase in a population (number) of microbes, and not the size of a microbe”. Eukaryotes growth Eukaryotes growth means increase in cell size without increase in cell number.

Microbial growth depends upon the metabolism of nutrients The requirements of microbial growth can be divided into 2 main categories :  Physical  Chemical

The Requirements for Growth (1)Physical Requirements (1)Physical Requirements Temperature Temperature pH pH Osmotic pressure Osmotic pressure (2) Chemical Requirements (2) Chemical Requirements Carbon Source Carbon Source Nitrogen, Sulfur and Phosphorus Nitrogen, Sulfur and Phosphorus Trace elements Trace elements Oxygen Oxygen Growth factors Growth factors

Microorganisms are classified based on the preferred range of temperature: Psychrophiles require temperatures below 20°C – cold loving microbes. Mesophiles grow best at temperatures ranging between about 20°C and 40°C - moderate temperature loving microbes. Thermophiles require temperatures above 45°C – heat loving microbes. Hyperthermophiles require temperatures above 80°C.

Temperature – each bacteria grow at a particular minimum, optimum, and maximum temperature.  Minimum growth temperature – lowest temperature at which the species grow.  Optimum growth temperature –temperature at which the species grow best.  Maximum growth temperature – highest temperature at which the growth is possible. Most of medically important species grow best at temperatures around 37°C (body temperature)

Dr. Dalia M. Mohsen Associate prof. of Microbiology This is helpful in food preparation business. Both the use of heat and cold allows for control of bacterial growth by either destroying the microbe (heat) or preventing further growth (cold). Refrigeration is the common method of preserving food supplies. Psychrotrophs – are the group of organisms that grow between 0°C and 20-30°C (in refrigerators) and cannot grow above 40°C.

Dr. Dalia M. Mohsen Associate prof. of Microbiology Chemical Requirements Carbon Source Carbon Source Nitrogen, Sulfur and Phosphorus Nitrogen, Sulfur and Phosphorus Trace elements Trace elements Oxygen Oxygen Growth factors Growth factors

Dr. Dalia M. Mohsen Associate prof. of Microbiology Carbon – most important molecule Carbon – most important molecule – Structural back bone (half of the dry weight of a bacterial cell), – Chemoheterotrophs – Chemoheterotrophs derive carbon from organic carbon sources like glucose, starch, cellulose, sucrose, lactose, and lipids. – Chemoautotrophs and photoautotrops derive carbon from – Chemoautotrophs and photoautotrops derive carbon from CO 2 Carbon Source Carbon Source

Dr. Dalia M. Mohsen Associate prof. of Microbiology Nitrogen – Used to form amino acids, proteins – Most bacteria decompose protein containing material to obtain nitrogen – A few bacteria use nitrogen gas directly from atmosphere - Nitrogen Fixation Nitrogen, Sulfur and Phosphorus Nitrogen, Sulfur and Phosphorus

Dr. Dalia M. Mohsen prof. of Microbiology Sulfur – Used In synthesis of amino acids like thiamine, biotin – Derived from SO 4 2  or H 2 S and sulphur containing amino acids. Phosphorus – Used In synthesis of DNA, RNA, ATP, and membranes – PO 4 3  is a source of phosphorus

Choose the correct answer 1-Microbial growth in prokaryotes is indicated by : [A] Increase the size of the cells [B] Increase the number of the cells [C] Decrease the metabolic rate of the cell. [D] Change the shape of the cell. [E] None of the above

Choose the correct answer:- 2-Psychrophilic bacteria grow in ………………. : [A] The temperature range of (10-50 o C). [B] 5% CO 2 [C] The temperature range of (0 -30 o C) [D] The temperature range of (70 o C -110 o C). [E] The temperature range ( o ).