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CHAPTER 6 Microbial Nutrition and Growth.doc

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BIOL 2905
Tanya Da Sylva

CHAPTER 6 Microbial Nutrition and Growth Objectives 1. Understand the various methods used by microbes for obtaining carbon, energy and electrons 2. Learn about the benefits and dangers of using oxygen in metabolism and how microbes can be classified by their ability to use or tolerate oxygen 3. Learn about other chemical and environmental requirements of microbes and how they can be classified by these needs. 4. Understand how microbes are cultured. 5. Learn how microbial populations grow in a culture medium. Content A. Patterns of metabolic pathways a. Vary with sources of carbon, energy and electrons or hydrogen atoms b. -Troph: suffix referring to eating c. Carbon i. Autotrophs: source is CO2 ii. Heterotrophs: source is reduced organic compounds d. Energy i. Phototrophs: energy source is light ii. Chemotrophs: energy source if from redox reactions involving inorganic and organic compounds (aerobic respiration, anaerobic respiration, fermentation) e. Electrons or hydrogen ions i. Organotrophs: from organic compounds, most organisms ii. Lithotrophs: from inorganic compounds; rarer f. The organisms we’ll be studying are chemoheterotrophs as humans supply carbon, electrons and energy required for our pathogens B. Oxygen requirements a. Toxic forms of oxygen (free radicals) i. Singlet oxygen: molecular O with e2ergized electrons - ii. Superoxide radical (O ) : 2uperoxide dismutase enzyme required to change superoxide radical into hydrogen peroxide and oxygen; anaerobes die because they lack this enzyme iii. Peroxide ion (O ): why hydrogen peroxide (H O is 2 2 2) antimicrobial; - Catalase: H O i2t2 H O and2O 2 - Peroxidase: H O into water and NAD (oxidized) 2 2 iv. Hydroxyl radical: most reactive of the four; enzymes above minimize production b. Types of organisms and need for oxygen i. Aerobes: use oxygen; have enzymes for detoxifying ii. Facultative anaerobes: can use anaerobic respiration or fermentation although prefer aerobic respiration; Escherichia iii. Aerotolerant anaerobes: don’t use but can tolerate oxygen because they have some of the enzymes that detoxify it (often peroxidases since they don’t make more O ); Lac2obacilli iv. Microaerophiles: very limited ability to detoxify oxygen; can tolerate smaller amounts than aerotolerant anaerobes; Helicobacter pylori v. Anaerobes: killed by oxygen because they can’t detoxify it; Clostridia vi. Obligate aerobes: algae, most fungi, protozoa and many prokaryotes vii. Facultative anaerobes: some yeast (fungi) and many prokaryotes viii. Other oxygen use patterns: many prokaryotes and a few protozoa c. Metabolic uses for oxygen i. Structural component of organic compounds (C,H,O,N) ii. Final electron acceptor in aerobic respiration pathway iii. Part of bacteriocidal response in organisms with lysosomes, neutrophils, macrophages, etc iv. Photosynthesis waste product C. Nitrogen requirements a. Growth limiting nutrient b. For use in metabolic reactions N must be in the form of ammonium or ammonia c. Nitrogen fixation: rare but essential function; N (atm2spheric gas)  NH 3 D. Other chemical requirements a. May be limiting (phosphorus) and may be accumulated by the organism (inclusion bodies: sulfur) b. Major elements: sulfur, magnesium, calcium, copper, iron, phosphorus, manganese c. Trace elements: selenium, zinc, cobalt d. Note that because of our similar metabolic pathways, in general, a (trace element), or micronutrient for a prokaryote is a micronutrient for eukaryotes (check out your multivitamin bottle) e. Growth factors: some organisms need none (algae and some bacteria = lithotropic photoautotrpohs), a few (many prokaryotes synthesize their own vitamins), others require standard vitamins and still others are fastidious requiring many different and complex organic compounds E. Temperature a. Effects on i. Shape of protein compounds ii. Rigidity/fluidity of cell membranes & other lipid structures b. Minimum growth temperature  optimum growth temperature  maximum growth temperature decreibes the temperature range of an organism c. Psychrophiles: optimum is a low temperature d. Mesophiles: medium temperatures; often our pathogens e. Thermophiles: grow well at high to boiling temperatures; include many Archaea and have been fruitful in providing unique enzymes important in genetic engineering (stable at high temperatures) f. Cold temperatures do not kill organisms but do slow the growth rate; extreme cold and drying (= lyophilization) may even be used to preserve organisms in type culture (standard strains) collections F. pH a. Effects on i. Shape of protein and nucleic acid compounds ii. Availablity for metabolic reactions b. Neutrophiles i. pH range of 6.5 to 7.5 ii. Our pathogenic organisms are of this type iii. Organisms producing acid waste products in a limited environment will eventually stop growing; has been used in food preservation (ex: sauerkraut & dill pickles) c. Acidophiles i. Obligate acidophiles: ex: chemoautotrophs that use sulfur as the acceptor of excess hydrogen ions to pr
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