University:
Bradley University
Course:
BIO 202 | Microbiology and Immunology
Academic year:

2024
Views:

75

Pages:

31
Author:

Gudrunecg9m

MICROBIOLOGY an introduction Microbial Growth Microbial Growth  Microbial growth is the increase in number of cells, not cell size Reproduction in Prokaryotes  Binary fission  Budding  Conidiospores (actinomycetes)  Fragmentation of filaments Binary Fission Figure 6.11 Microbial Growth  Generation Time  Time required for a cell to divide (and its population to double)  E. coli: 20 minutes (under ideal conditions) Figure 6.14 The Requirements for Growth: Physical Requirements  Temperature  Minimum growth temperature  Optimum growth temperature  Maximum growth temperature 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 0O and 30OC  Cause food spoilage  Hyperthermophiles (extreme thermophiles): optimum growth temperature of 80OC or higher Temperature Figure 6.1 Psychrotrophs Figure 6.2 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 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 The Requirements for Growth: Physical Requirements Figure 6.4 The Requirements for Growth: Chemical Requirements  Carbon  Structural organic molecules, energy source  Chemoheterotrophs use organic carbon sources  Autotrophs use CO2 The Requirements for Growth: Chemical Requirements  Nitrogen  In amino acids and proteins  Most bacteria decompose proteins  Some bacteria use NH4+ or NO3–  A few bacteria use N2 in nitrogen fixation  Sulfur  In amino acids, thiamine and biotin  Most bacteria decompose proteins  Some bacteria use SO42– or H2S  Phosphorus  In DNA, RNA, ATP, and membranes  PO43– is a source of phosphorus The Requirements for Growth: Chemical Requirements  Trace elements  Inorganic elements required in small amounts  Usually as enzyme cofactors The Requirements for Growth: Chemical Requirements  Oxygen (O2) Table 6.1 The Requirements for Growth: Chemical Requirements  Organic growth factors  Organic compounds obtained from the environment  Vitamins, amino acids, purines, and pyrimidines Culture Media and Obtaining Pure Cultures 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 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 Petri dish  Shallow dishes with a lid that nests over the bottom to prevent contamination 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)  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). 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 Streak Plate Figure 6.10a–b Measuring Microbial Growth Direct methods Indirect methods  Plate counts  Turbidity  Filtration  Metabolic activity  MPN  Dry weight  Direct microscopic count  Dry weight Direct Measurements of Microbial Growth Figure 6.19, steps 1, 3 Estimating Bacterial Numbers by Indirect Methods  Turbidity Figure 6.20

Microbiology Notes

Related Documents

Recommended Documents

Description

Related Documents

Free up your schedule!

Take 5 seconds to unlock