Nutrition and Growth

Nutrition Bacterial growth depends on: Nutritional factors Physical factors Nutritional Factors Essential elements Macronutrients (structure & metabolism) Large quantities: Carbon, Hydrogen, Oxygen, Nitrogen, Phosphorus, & Sulfur Small quantities: Minerals (Salt, Ca++, Fe++, Mg++, K+, Mn++) essential for ribosomes Micronutrients (enzymes & pigments) Needed in small amounts: Zn, Mn, Mo Physical Factors Temp pH O2 Salt Iron Metabolism Fe++ (Ferrous Iron) for cytochrome synthesis Transferrin in blood Energy Source Carbon is necessary for bacterial growth. Self-feeding autotrophs synthesize all their organic compounds by using CO2 as a carbon source. Photoautotrophs: Light + CO2 Chemoautotrophs: Inorganic compounds + CO2 Heterotrophs require preformed organic compounds made by other living things. Light + Organic Compounds Organic Compounds + Organic Compounds Chemoorganoheterotrophs (E. coli) Capnophiles require a high concentration of CO2 and low levels of O2 (e.g., Haemophilus influenzae, Neisseria gonorrhoeae). Nitrogen Non-exacting bacteria utilize inorganic sources of nitrogen. Exacting bacteria utilize organic sources of nitrogen. Growth Factors Cofactor for enzymes, protein synthesis, DNA B-complex, as purines & pyrimidines, yeast extract, blood Fastidious: require various growth factors. Non-fastidious: don't require special growth factors. Auxotrophs: mutant strain, require some growth factor not needed from the parent strain. Physical factors Temp Psychrophils & grow < 20°C (most saprophytes/pseudomonas) Mesophils & grow 25-40°C (most pathogenic bacteria grow 37°C except Yersinia pestis 27°C) Thermophiles & grow 55-80°C (Geobacillus stearothermophilus) Extreme thermophiles & grow 80-113°C (usually Archaea) pH Optimum pH of most pathogenic bacteria is 7.2-7.6 Neutrophils grow 7 pH (natural) Acidophils grow < 7 pH (Lactobacilli < 4.9) Alkalophils grow > 7 pH (Vibrio cholera 8.2-8.9) O2 requirements Superoxide dismutase Low O2: Superoxide dismutase → H2O2 → Catalase Good in aerobic bacteria Absence in anaerobic bacteria ATP → H2O2 Catalase 1. Obligate aerobes Require O2 Grow only on the surface Ex: Pseudomonas, Mycobacterium Tuberculosis, Bacillus, Brucella, Nocardia 2. Facultative anaerobes Able to live aerobically or anaerobically Grow better in the presence of O2 Ex: E. coli, S. aureus 3. Microaerophilic Grow at low O2 (5-10%) Growth just below the surface Ex: Campylobacter jejuni, Helicobacter pylori 4. Obligate anaerobes Grow only in the absence of O2 Catalase & superoxide dismutase absent Ex: Clostridium tetani 5. Aerotolerant Don't use O2 but can tolerate it Growth throughout H2O availability & Salt Concentration Non-halophiles: No requirement for high salt concentration Halophiles: Microorganisms that require salt to grow Halotolerant: Microorganisms that can grow over a wide range of salt concentration Ex: Staphylococcus aureus Bacterial Growth Increase in number of cells, not in size. By binary fission (asexually) DNA replication Septum formation Cell separation Generation time (doubling time) is the time required for a bacterium to give 2 daughter cells or to complete 1 cell cycle. Examples: E. coli: 20 minutes Mycobacterium tuberculosis: 12-24 hours Mycobacterium leprae: 12-13 days [Growth Curve] Lag phase: Adaptation Synthesis of enzymes Recovery from physical damage No cell division Log phase (Exponential phase): Increase in number of cells Synthesis of new enzymes Doubling time Exponential growth Stationary phase: Death rate = Reproduction rate Nutrients depleted Waste products accumulate Cells stop dividing Decline phase (Death phase): Death rate > Reproduction rate Cells die Recovery/Convalescence period Phase Divide Death Total Count Viable Count Special Features Enzymes & Metabolites Morphology Lag No No Flat Flat Enzymes Synthesis Small size Log Yes No ↑ (reproduction) ↑ (reproduction) Uniformly stained Metabolically active Small size Stationary Yes Yes Flat Flat Gram Variable Produce granules, spores, exotoxins, antibiotics, bacteriocin Max size Decline No Yes ↓ (reproduction) ↓ (death) Involution Forms abnormal bacteria