Bacterial Growth and Nutrition Bacterial nutrition and culture
Bacterial Growth and Nutrition • • Bacterial nutrition and culture media Chemical and physical factors affecting growth The nature of bacterial growth Methods for measuring population size http: //diverge. hunter. cuny. edu/~weigang/Images/0611_binaryfission_1. jpg 1
The First Law of Thermodynamics • Energy cannot be created or destroyed. – It is interchangeable with matter. – Chemical energy; nuclear energy: E = mc 2 • In order to grow, bacteria need a source of raw materials and energy – Source can be the same (e. g. glucose) or different (e. g. carbon dioxide and sunlight). – Living things can’t turn energy into raw materials, only use it to assemble raw materials. – Bacteria can’t grow on nothing! 2
Where do raw materials come from? • Bacteria acquire energy from oxidation of organic or inorganic molecules, or from sunlight. • Growth requires raw materials: some form of carbon. • Autotrophs vs. heterotrophs – Auto=self; hetero=other; troph=feeding. – Autotrophs use carbon dioxide – Heterotrophs use pre-formed organic compounds (molecules made by other living things). – Humans and medically important bacteria are heterotrophs. 3
Essentials of Bacterial nutrition 4 • Macronutrients: needed in larger amounts – Needed in large quantities: CHONPS • Carbon, hydrogen, oxygen, nitrogen, phosphorous, and sulfur. H and O are common. Sources of C, N, P, and S must also be provided. – Macronutrients needed in smaller amounts: • Mineral salts such as Ca+2, Fe+3, Mg+2, K+ • Micronutrients = trace elements; – needed in very tiny amounts; e. g. Zn+2, Mo+2, Mn+2
Element % dry wgt Source Carbon 50 organic compounds or CO 2 Oxygen 20 H 2 O, organic compounds, CO 2, and O 2 Nitrogen 14 NH 3, NO 3, organic compounds, N 2 Hydrogen 8 H 2 O, organic compounds, H 2 Phosphorus 3 inorganic phosphates (PO 4) Sulfur 1 SO 4, H 2 S, So, organic sulfur compounds Potassium 1 Potassium salts Magnesium 0. 5 Magnesium salts Calcium 0. 5 Calcium salts Iron 0. 2 Iron salts http: //textbookofbacteriology. net/nutgro. html 5
Chemical form must be appropriate • Not all bacteria can use the same things – Some molecules cannot be transported in – Enzymes for metabolizing it might not be present – Chemical may be used, but more expensive – These differences are used for identification • Some chemicals are inert or physically unusable – Relatively few bacteria (and only bacteria) use N 2 – Diamonds, graphite are carbon, but unusable – P always in the form of phosphate 6
Make it, or eat it? 7 • Some bacteria are remarkable, being able to make all the organic compounds needed from a single C source like glucose. • For others: – Vitamins, amino acids, blood, etc. added to a culture medium are called growth factors. – Bacteria that require a medium with various growth factors or other components and are hard to grow are referred to as fastidious.
Feast or famine: normal is what’s normal for you: Oligotrophs vs. copiotrophs • Oligo means few; oligotrophs are adapted to life in environments where nutrients are scarce – For example, rivers, other clean water systems. • Copio means abundant, as in “copious” – The more nutrients, the better. – Medically important bacteria are copiotrophs. – Grow rapidly and easily in the lab. 8
Responses of microbes to nutritional deficiency • Extracellular molecules collect nutrients – Siderophores, hemolysins collect iron – extracellular enzymes break down polymers • Cells enter Semi-starvation state: – slower metabolism, smaller size. • Sporulation and “resting cells”: – cells have very low metabolic rate – Some cells change shape, develop thick coat – Endospores form within cells; very resistant. – Spores are for survival, triggered by low nutrients 9
Endospore formation http: //www. microbe. org/art/endospore_cycle. jpg 10
Responses of microbes to other environmental stresses 11 • Compatible solutes: small neutral molecules accumulated in cytoplasm when external environment is hypertonic. • Heat shock proteins and other stress proteins – Bacteria express additional genes that code for protective proteins. http: //www. thermera. com/ima ges/Betaine. gif
Culture Medium 12 • Defined vs. Complex – Defined has known amounts of known chemicals. – Complex: hydrolysates, extracts, etc. • Exact chemical composition is not known. • Selective and differential – Selective media limits the growth of unwanted microbes or allows growth of desired ones. – Differential media enables “differentiation” between different microbes. – A medium can be both.
Defined Medium for Cytophagas/Flexibacters Component K 2 HPO 4 0. 10 KH 2 PO 4 0. 05 Mg. Cl 2 0. 36 Na. HCO 3 0. 05 {Ca. Cl 2 1 ml* {Ba. Cl 2. 2 H 2 O Na acetate 0. 01 Fe. Cl. 7 H 2 O RNA 0. 10 alanine 0. 15 arginine 0. 20 aspartic acid glutamic acid grams 0. 2 ml* 0. 30 0. 55 glycine histidine isoleucine lysine phenylalanine proline serine threonine valine 0. 02 0. 20 0. 30 0. 20 0. 40 0. 30 0. 50 0. 30 13
Physical requirements for growth • Prefixes and suffixes: • Bacteria are highly diverse in the types of conditions they can grow in. – Optimal or required conditions implied by “-phile” meaning “love” • Some bacteria prefer other conditions, but can tolerate extremes – Suffix “-tolerant” • Note the difference! http: //www. kodak. com/global/images/en/health/film. Imaging/thermometer. gif 14
Oxygen: friend or foe? 15 • Early atmosphere of Earth had none – First created by cyanobacteria using photosynthesis – Iron everywhere rusted, then collected in atmosphere • Strong oxidizing agent • Reacts with certain organic molecules, produces free radicals and strong oxidizers : – Singlet oxygen, H 2 O 2(peroxide), O 3 - (superoxide), and hydroxyl (OH-) radical.
Protections of bacteria against oxygen 16 – Bacteria possess protective enzymes, catalase and superoxide dismutase. – Catalase breaks down hydrogen peroxide into water and oxygen gas. – Superoxide dismutase breaks superoxide down into peroxide and oxygen gas. – Anaerobes missing one or both; slow or no growth in the presence of oxygen. Fe 3+ -SOD + O 2 - → Fe 2+ -SOD + O 2 - + 2 H+ → Fe 3+ -SOD + H 2 O 2
Relation to Oxygen 17 • Aerobes: use oxygen in metabolism; obligate. A: aerobe B: microaerophile • Microaerophiles: require oxygen (also obligate), but in small amounts. • Anaerobes: grow without oxygen; SEE NEXT • Capnophiles: require larger amounts of carbon dioxide than are found normally in air.
Anaerobes grow without O 2 18 • Classifications vary, but our definitions: – Obligate (strict) anaerobes: killed or inhibited by oxygen. – Aerotolerant anaerobes: do not use oxygen, but not killed by it. C: could be facultative – Facultative anaerobes: can or aerotolerant. D: strict anaerobe grow with or without oxygen
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