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Chapter 6 Microbial Nutrition and Growth Nutrition is a process by which all living organisms obtain substances from their environment to convert to metabolic uses. Nutrients are categorized by the amount required (macronutrients or micronutrients), by chemical structure (organic or inorganic), and by their importance to the organism’s survival (essential or nonessential). Microorganisms are classified both by the chemical form of their nutrients and the energy sources they utilize. Although the chemical form of nutrients varies widely, all organisms require six elements—carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur—to survive, grow, and reproduce. Nutrients are transported into microorganisms by two kinds of processes: active transport that expends energy and passive transport that does not need energy input. The environmental factors that control microbial growth are temperature; gases; pH; osmotic, hydrostatic and atmospheric pressure; radiation; and other organisms in their habitats. Environmental factors control microbial growth mainly by their influence on microbial enzymes. Three cardinal temperatures for a microorganism describe its temperature range and the temperature at which it grows best. These are the minimum temperature, the maximum temperature, and the optimum temperature. Microorganisms are classified by their temperature requirements as psychrophiles, mesophiles, or thermophiles. Most eukaryotic microorganisms are aerobic, whereas bacteria vary widely in their oxygen requirements from obligately aerobic to anaerobic. Microorganisms live in association with other species that range from mutually beneficial symbiosis to parasitism and antagonism. Biofilms are examples of complex synergistic communities of microbes that behave differently than free-living microorganisms. The splitting of a parent bacterial cell to form a pair of similar size daughter cells is known as binary fission. Microbial growth refers both to increase in cell size and increase in number of cells in a population. The generation time is a measure of the growth rate of a microbial population. It varies in length according to environmental conditions. Microbial cultures in a nutrient-limited batch environment exhibit four distinct stages of growth: the lag phase, the exponential growth (log) phase, the stationary phase, and the death phase. Microbial cell populations show distinct phases of growth in response to changing nutrient and waste conditions. Population growth can be quantified by measuring colony numbers, the turbidity of a solution, and direct cell counts. 6.1 Microbial Nutrition 1. List the essential nutrients of a bacterial cell. 2. Differentiate between macronutrients and micronutrients. 3. Construct four different terms that describe an organism’s sources of carbon and energy. 4. Define saprobe and parasite. 5. Discuss diffusion and osmosis. 6. Identify the effects on a cell of isotonic, hypotonic, and hypertonic conditions. 7. Name two types of passive transport and three types of active transport. 6.2 Environmental Factors That Influence Microbes 8. Name five types of bacteria based on their temperature preferences. 9. Explain how different organisms deal with oxygen. 10. Name three physical factors besides temperature and oxygen requirements that microbes must contend with. 11. List and describe the five types of associations microbes can have with their hosts. 12. Discuss characteristics of biofilms that differentiate them from planktonic bacteria. 6.3 The Study of Bacterial Growth 13. Describe the main way that bacteria divide. 14. Define doubling time and how it relates to exponential growth. 15. Compare and contrast the four phases of growth in a bacterial growth curve. 16. Identify three methods besides a growth curve to count bacteria. Key Terms Nutrition Nutrients Essential nutrient Macronutrients Micronutrients Trace elements Inorganic nutrient Organic nutrient Heterotroph Autotroph Phototroph Chemotroph Photoautotroph Chemoautotrophs Lithoautotrophs Chemoheterotrophs Saprobes Parasites Obligate Facultative Opportunistic Pathogens Passive transport Active transport Bulk transport Diffusion Osmosis Permeable Isotonic Hypotonic Hypertonic Facilitated diffusion Group translocation Endocytosis Phagocytosis Pinocytosis Optimum temperature Psychrophile Mesophile Thermophile Aerobe Anaerobe Microaerophile Aerotolerant Capnophiles Acidophiles Alkalinophiles Halophiles Barophiles Symbiosis Mutualism Commensalism Parasitism Synergism Antagonism Normal microbial flora Binary fission Exponential Lag phase Exponential (log) phase Stationary phase Death phase Direct (total) cell count Viable nonculturable (VNC) Extreme thermophile Growth curve Quorum sensing Osmophiles Hydrogen peroxide