Transcript Slide 1
• Micobial Growth 2008 Microbial Growth • Microbial growth = increase in number of cells, not cell size 2008 The Requirements for Growth: Physical Requirements • Temperature • Minimum growth temperature • Optimum growth temperature • Maximum growth temperature 2008 Temperature 2008 Figure 6.1 Psychrotrophs • Grow between 0°C and 20-30°C • Cause food spoilage 2008 Psychrotrophs 2008 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 2008 The Requirements for Growth: Physical Requirements • Osmotic Pressure • Hypertonic environments, increase salt or sugar, cause plasmolysis • Extreme or obligate halophiles require high osmotic pressure • Facultative halophiles tolerate high osmotic pressure 2008 The Requirements for Growth: Physical Requirements 2008 Figure 6.4 The Requirements for Growth: Chemical Requirements • Carbon • Structural organic molecules, energy source • Chemoheterotrophs use organic carbon sources • Autotrophs use CO2 2008 The Requirements for Growth: Chemical Requirements • Nitrogen • In amino acids, proteins • Most bacteria decompose proteins • Some bacteria use NH4+ or NO3 • A few bacteria use N2 in nitrogen fixation • Sulfur • In amino acids, thiamine, biotin • Most bacteria decompose proteins • Some bacteria use SO42 or H2S • Phosphorus • In DNA, RNA, ATP, and membranes • PO43 is a source of phosphorus 2008 The Requirements for Growth: Chemical Requirements • Trace Elements • Inorganic elements required in small amounts • Usually as enzyme cofactors 2008 The Requirements for Growth: Chemical Requirements • Oxygen (O2) obligate aerobes 2008 Faultative anaerobes Obligate anaerobes Aerotolerant anaerobes Microaerophiles Toxic Forms of Oxygen • Singlet oxygen: O2 boosted to a higher-energy state • Superoxide free radicals: O2 • Peroxide anion: O22 • Hydroxyl radical (OH) 2008 The Requirements for Growth: Chemical Requirements • Organic Growth Factors • Organic compounds obtained from the environment • Vitamins, amino acids, purines, pyrimidines 2008 Culture Media • Culture Medium: Nutrients prepared for microbial growth • Sterile: No living microbes • Inoculum: Introduction of microbes into medium • Culture: Microbes growing in/on culture medium 2008 Agar • Complex polysaccharide • 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 2008 Culture Media • Chemically Defined Media: Exact chemical composition is known • Complex Media: Extracts and digests of yeasts, meat, or plants • Nutrient broth • Nutrient agar 2008 Culture Media 2008 Table 6.2 & 6.4 Anaerobic Culture Methods • Reducing media • Contain chemicals (thioglycollate or oxyrase) that combine O2 • Heated to drive off O2 2008 Anaerobic Culture Methods • Anaerobic jar 2008 Figure 6.5 Anaerobic Culture Methods • Anaerobic chamber 2008 Figure 6.6 Capnophiles require high CO2 • Candle jar • CO2-packet 2008 Figure 6.7 Selective Media • Suppress unwanted microbes and encourage desired microbes. 2008 Figure 6.9b, c Differential Media • Make it easy to distinguish colonies of different microbes. 2008 Figure 6.9a Enrichment Media • Encourages growth of desired microbe • Assume a soil sample contains a few phenoldegrading bacteria and thousands of other bacteria • Inoculate phenol-containing culture medium with the soil and incubate • Transfer 1 ml to another flask of the phenol medium and incubate • Transfer 1 ml to another flask of the phenol medium and incubate • Only phenol-metabolizing bacteria will be growing 2008 • 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) 2008 Streak Plate 2008 Figure 6.10a, b Preserving Bacteria Cultures • Deep-freezing: -50°to -95°C • Lyophilization (freeze-drying): Frozen (-54° to -72°C) and dehydrated in a vacuum 2008 Reproduction in Prokaryotes • Binary fission • Budding • Conidiospores (actinomycetes) • Fragmentation of filaments 2008 Binary Fission 2008 Figure 6.11 2008 Figure 6.12b If 100 cells growing for 5 hours produced 1,720,320 cells: 2008 2008 Figure 6.13 2008 Figure 6.14 Direct Measurements of Microbial Growth • Plate Counts: Perform serial dilutions of a sample 2008 Figure 6.15, top portion Plate Count • Inoculate Petri plates from serial dilutions 2008 Figure 6.16 Plate Count • After incubation, count colonies on plates that have 25250 colonies (CFUs) 2008 Figure 6.15 Direct Measurements of Microbial Growth • Filtration 2008 Figure 6.17a, b Direct Measurements of Microbial Growth • Multiple tube MPN test • Count positive tubes and compare to statistical MPN table. 2008 Figure 6.18b Direct Measurements of Microbial Growth • Direct Microscopic Count 2008 Direct Measurements of Microbial Growth 2008 Figure 6.19 Estimating Bacterial Numbers by Indirect Methods • Turbidity 2008 Figure 620 Estimating Bacterial Numbers by Indirect methods • Metabolic activity • Dry weight 2008