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PowerPoint to accompany Microbiology: A Systems Approach Cowan/Talaro Chapter 7 Elements of Microbial Nutrition, Ecology, and Growth Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 7 Topics – – – – Microbial Nutrition Transport Across the Membrane Environmental Factors Microbial Growth 2 Table 7.1 3 Microbial Nutrition • Definitions – – – – – – Nutrition Essential nutrient Macronutrient Micronutrient Inorganic nutrient Organic nutrient 4 Bacteria are composed of different elements and molecules, with water (70%) and proteins (15%) being the most abundant. Table 7.2 Analysis of the chemical composition of an E. coli cell. 5 Sources of essential nutrients • Required for metabolism and growth – Carbon source – Energy source 6 Carbon source • Heterotroph (depends on other life forms) – Organic molecules – Ex. Sugars, proteins, lipids • Autotroph (self-feeders) – Inorganic molecules – Ex. CO2 7 Sources of Essential Nutrients • • • • • Nitrogen Oxygen Hydrogen Phosphorous Sulfur 8 Miscellaneous Nutrients • Mineral Ions – K, Na, Ca, Mg, Z • Trace Elements – Cu, Co, Ni, Mb, Mn, Si, B, I • Growth Factors 9 Growth factors • Essential organic nutrients • Not synthesized by the microbe, and must be supplemented • Ex. Amino acids, vitamins 10 Nutritional Types • Carbon Source – Organic – “Hetero” – Inorganic – “Auto” • Energy Source – Light – “Photo” – Chemical – “Chemo” 11 Energy source • • • • Photoautotrophs Chemoautotrophs Photoheterotrophs Chemoheterotrophs 12 Photoautotroph • Derive their energy from sunlight • Transform light rays into chemical energy • Primary producers of organic matter for heterotrophs • Primary producers of oxygen • Ex. Algae, plants, cyanobacteria 13 Fig. 4.27b 14 Chemoautotrophs • Carbon Source is Inorganic ( CO2) • Two types – Chemical Energy can be organic or inorganic • Ex. Methanogens, Lithoautotrophs 15 Methanogens are an example of a chemoautotroph. Fig. 7.1 Methane-producing archaea 16 Photoheterotrophs • Light energy • Organic Carbon Source • Purple & Green Photosyntheic Bacteria 17 Fig. 4.28 18 Chemoheterotrophs • Derive both carbon and energy from organic compounds – Saprobic • decomposers of plant litter, animal matter, and dead microbes – Parasitic • Live in or on the body of a host 19 Representation of a saprobe and its mode of action. Fig. 7.2 Extracellular digestion in a saprobe with a cell wall. 20 Summary of the different nutritional categories based on carbon and energy source. Table 7.3 Nutritional categories of microbes by energy and carbon source. 21 Transport mechanisms • Osmosis • Passive Transport – Simple Diffusion – Facilitated Diffusion • Active transport • Endocytosis 22 Osmosis • Diffusion of water through a permeable but selective membrane • Water moves toward the higher solute concentrated areas – Isotonic – Hypotonic – Hypertonic 23 Representation of the osmosis process. Fig. 7.3 Osmosis, the diffusion of water through a selectively permeable membrane 24 Cells with- and without cell walls, and their responses to different osmotic conditions (isotonic, hypotonic, hypertonic). Fig. 7.4 Cell responses to solutions of differing osmotic content. 25 Fig. 7.4 26 Fig. i7.p211a 27 Diffusion • Net movement of molecules from a high concentrated area to a low concentrated area • No energy is expended (passive) • Concentration gradient and permeability affect movement 28 A cube of sugar will diffuse from a concentrated area into a more dilute region, until an equilibrium is reached. Fig. 7.5 Diffusion of molecules in aqueous solutions 29 Facilitated diffusion • Transport of polar molecules and ions across the membrane • No energy is expended (passive) • Carrier protein facilitates the binding and transport – Specificity – Saturation – Competition 30 Representation of the facilitated diffusion process. 31 Fig. 7.6 Facilitated diffusion Active transport • Transport of molecules against a gradient • Requires energy (active) • Requires a transport protein • sugars, amino acids, organic acids, phosphates and metal ions. 32 Fig. 7.7a 33 Fig. 7.7b 34 Endocytosis • Substances are taken in, but are not transported through the membrane. • Requires energy (active) • Common for eucaryotes – Phagocytosis – solid particles – Pinocytosis - liquids 35 Fig. 7.7c 36 Example of the permease, group translocation, and endocytosis processes. Fig. 7.7 Active transport 37 Summary of the transport processes in cells. Table 7.4 Summary of transport processes in cells 38 Environmental Factors • • • • • • Temperature Gas pH Osmotic pressure Other environmental factors Microbial associations 39 Temperature • • • • • • For optimal growth and metabolism Psychrophile – 0 to 15 °C Psychrotrophs – 20-30°C Mesophile20 to 40 °C Thermophile- 45 to 80 °C Hyperthermophiles - > 80° C 40 Growth and metabolism of different ecological groups based on ideal temperatures. Fig. 7.8 Ecological groups by temperature 41 Example of a psychrophilic photosynthetic Red snow organism. Fig. 7.9 Red snow 42 Gas • Two gases that most influence microbial growth – Oxygen • Respiration • Oxidizing agent – Carbon dioxide 43 Oxidizing agent • Oxygen metabolites are toxic – – – – Singlet Oxygen Superoxide Free Radicals Hydrogen Peroxide Hydroxyl Radicals • These toxic metabolites must be neutralized for growth 44 Five categories of bacteria • • • • • Obligate aerobe Facultative anaerobe Obligate anaerobe Aerotolerant Anaerobes Microaerophiles 45 Obligate aerobe • Requires oxygen for metabolism • Possess enzymes that can neutralize the toxic oxygen metabolites – Superoxide dismutase and catalase • Ex. Most fungi, protozoa, and bacteria 46 Facultative anaerobe • Does not require oxygen for metabolism, but can grow in its presence • During minus oxygen states, anaerobic respiration or fermentation occurs • Possess superoxide dismutase and catalase • Ex. Gram negative pathogens 47 Obligate anaerobes • Cannot use oxygen for metabolism • Do not possess superoxide dismutase and catalase • The presence of oxygen is toxic to the cell 48 Aerotolerant Anaerobes • Can tolerate oxygen but don’t use it for growth 49 Microaerophiles • Require Oxygen, but only in small amounts • Don’t make enough enzymes to detoxify toxic forms of oxygen if they are exposed to normal atmosphere 50 Anaerobes must grow in an oxygen minus environment, because toxic oxygen metabolites cannot be neutralized. Fig. 7.10 Culturing technique for anaerobes 51 Thioglycollate broth enables the identification of aerobes, facultative anaerobes, and obligate anaerobes. Reducing Media Fig. 7.11 Use of thioglycollate broth to demonstrate oxygen requirements. 52 Fig. 7.10b 53 pH • Cells grow best between pH 6-8 • Exceptions would be acidophiles (pH 0), and alkalinophiles (pH 10). 54 Osmotic pressure • • • • • Halophiles Withstand hypertonic conditions Some requires high salt concentrations Ex. Halobacterium Some can survive high salt conditions but is not required – Ex. Staphylococcus aureus 55 Other factors • Radiation- Spores or pigments help withstand UV, infrared • Barophiles – withstand high pressures • Spores and cysts- can survive dry habitats 56 Ecological association • Influence microorganisms have on other microbes – Symbiotic relationship – Non-symbiotic relationship 57 Symbiotic • Organisms that live in close nutritional relationship • Types – Mutualism – both organism benefit – Commensalism – one organisms benefits – Parasitism – host/microbe relationship 58 An example of commensalism, where Staphylococcus aureus provides vitamins and amino acids to Haemophilus influenzae. Fig. 7.12 Satellitism, a type of commensalism 59 Non-symbiotic • Organisms are free-living, and do not rely on each other for survival • Types – Synergism – shared metabolism, not required – Antagonism- competition between microorganisms 60 Interrelationships between microbes and humans • Can be commensal, parasitic, and synergistic • Normal Microbial Flora are beneficial – Mutualistic – Ex. E. coli produce vitamin K for the host 61 Microbial Growth • • • • Binary fission Generation time Growth curve Enumeration of bacteria 62 Binary fission • The division of a bacterial cell • Parental cell enlarges and duplicates its DNA • Septum formation divides the cell into two separate chambers • Complete division results in two identical cells 63 Representation of the steps in binary fission of a rod-shaped bacterium. Fig. 7.13 Steps in binary fission of a rod-shaped bacterium. 64 Generation time • The time required for a complete division cycle (doubling) • Length of the generation time is a measure of the growth rate • Exponentials are used to define the numbers of bacteria after growth 65 Representation of how a single bacterium doubles after a complete division, and how this can be plotted using exponentials. Fig. 7.14 The mathematics of population growth 66 Fig. 7.14b 67 Growth curve • • • • Lag phase Log phase Stationary phase Death phase 68 Lag phase • Cells are adjusting, enlarging, and synthesizing critical proteins and metabolites • Not doubling at their maximum growth rate 69 Log phase • Maximum exponential growth rate of cell division • Adequate nutrients • Favorable environment 70 Stationary phase • Survival mode – depletion in nutrients, released waste can inhibit growth • When the number of cells that stop dividing equal the number of cells that continue to divide 71 Death phase • A majority of cells begin to die exponentially due to lack of nutrients • A chemostat will provide a continuous supply of nutrients, thereby the death phase is never achieved. 72 The four main phases of growth in a bacterial culture. Fig. 7.15 The growth curve in a bacterial culture. 73 Measuring Microbial Growth • Direct Methods – Plate Counts – Direct cell count – Automated devices • Coulter counter • Flow cytometer • Indirect Methods – Turbidity • Spectrophotometer – Measure Metabolic Activity 74 Fig. i7.6 75 The direct cell method counts the total dead and live cells in a special microscopic slide containing a premeasured grid. Fig. 7.17 Direct microscopic count of bacteria. 76 A Coulter counter uses an electronic sensor to detect and count the number of cells. Fig. 7.18 Coulter counter 77 The greater the turbidity, the larger the population size. Fig. 7.16 Turbidity measurements as indicators of growth 78