M I C R O B I O L O G Y

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1 ninth edition TORTORA FUNKE CASE M I C R O B I O L O G Y a n i n t r o d u c t i o n 6 Microbial Growth PowerPoint Lecture Slide Presentation prepared by Christine L. Case

2 Microbial Growth Microbial growth is the increase in number of cells, not cell size

3 Reproduction in Prokaryotes Binary fission Budding Conidiospores (actinomycetes) Fragmentation of filaments

4 Binary Fission Figure 6.11

5 Microbial Growth Generation Time Time required for a cell to divide (and its population to double) E. coli: 20 minutes (under ideal conditions)

6 Figure 6.14

7 The Requirements for Growth: Physical Requirements Temperature Minimum growth temperature Optimum growth temperature Maximum growth temperature

8 The Requirements for Growth: Physical Requirements Temperature Psychrophiles: cold-loving microbes Mesophiles: moderate temperature-loving microbes Thermophiles: heat-loving microbes Psychrotrophs: capable of growth between about 0 O and 30 O C Cause food spoilage Hyperthermophiles (extreme thermophiles): optimum growth temperature of 80 O C or higher

9 Temperature Figure 6.1

10 Psychrotrophs Figure 6.2

11 The Requirements for Growth: Physical Requirements ph Most bacteria grow between ph 6.5 and 7.5 Molds and yeasts grow between ph 5 and 6 Acidophiles grow in acidic environments Chemical buffers are included in growth media to neutralize acids and maintain proper ph

12 The Requirements for Growth: Physical Requirements Osmotic pressure Microorganisms obtain almost all their nutrients in solution from the surrounding water Hypertonic environments, increase salt or sugar, cause plasmolysis (shrinkage of the cell s cytoplasm) Extreme or obligate halophiles require high osmotic pressure Facultative halophiles tolerate high osmotic pressure

13 The Requirements for Growth: Physical Requirements Figure 6.4

14 The Requirements for Growth: Chemical Requirements Carbon Structural organic molecules, energy source Chemoheterotrophs use organic carbon sources Autotrophs use CO 2

15 The Requirements for Growth: Chemical Requirements Nitrogen In amino acids and proteins Most bacteria decompose proteins Some bacteria use NH 4 + or NO 3 A few bacteria use N 2 in nitrogen fixation Sulfur In amino acids, thiamine and biotin Most bacteria decompose proteins Some bacteria use SO 4 2 or H 2 S Phosphorus In DNA, RNA, ATP, and membranes PO 4 3 is a source of phosphorus

16 The Requirements for Growth: Chemical Requirements Trace elements Inorganic elements required in small amounts Usually as enzyme cofactors

17 The Requirements for Growth: Chemical Requirements Oxygen (O 2 ) Table 6.1

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19 The Requirements for Growth: Chemical Requirements Organic growth factors Organic compounds obtained from the environment Vitamins, amino acids, purines, and pyrimidines

20 Culture Media and Obtaining Pure Cultures

21 Culture Media Culture medium: Nutrient material prepared for the growth of microorganisms in a laboratory Sterile: contains no living microorganism Inoculum: microbes introduced into a culture medium to initiate growth Culture: microbes that grow and multiply in or on a culture medium

22 Agar Complex polysaccharide Derived from algae Used as solidifying agent for culture media in Petri plates, slants, and deeps Generally not metabolized by microbes Liquefies at 100 C Solidifies ~40 C

23 Petri dish Shallow dishes with a lid that nests over the bottom to prevent contamination

24 Culture Media Chemically defined media: Exact chemical composition is known Complex media: Extracts and digests of yeasts, meat, or plants Nutrient broth (liquid form) Nutrient agar (when agar is added)

25 A pure culture contains only one species or strain. A colony is a population of cells arising from a single cell or spore or from a group of attached cells. A colony is often called a colony-forming unit (CFU).

26 Streak Plate The isolation method most commonly used to get pure cultures. Sterile inoculating loop is dipped into a mixed culture Streaked in a pattern over the nutrient medium Last cells to be rubbed off the loop are far enough apart to grow into isolated colonies Colonies can be picked up with an inoculating loop and transferred to a test tube of nutrient medium to form a pure culture Figure 6.10a b

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28 Streak Plate Figure 6.10a b

29 Measuring Microbial Growth Direct methods Plate counts Filtration MPN Direct microscopic count Dry weight Indirect methods Turbidity Metabolic activity Dry weight

30 Direct Measurements of Microbial Growth Figure 6.19, steps 1, 3

31 Estimating Bacterial Numbers by Indirect Methods Turbidity Figure 6.20