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1 Bacterial Growth and Nutrition Bacterial nutrition and culture media Chemical and physical factors affecting growth The nature of bacterial growth Methods.

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Presentation on theme: "1 Bacterial Growth and Nutrition Bacterial nutrition and culture media Chemical and physical factors affecting growth The nature of bacterial growth Methods."— Presentation transcript:

1 1 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

2 2 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!

3 3 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.

4 4 Essentials of Bacterial nutrition 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

5 5 Element% dry wgtSource Carbon50organic compounds or CO 2 Oxygen20H 2 O, organic compounds, CO 2, and O 2 Nitrogen14NH 3, NO 3, organic compounds, N 2 Hydrogen8H 2 O, organic compounds, H 2 Phosphorus3inorganic phosphates (PO 4 ) Sulfur1 SO 4, H 2 S, S o, organic sulfur compounds Potassium1Potassium salts Magnesium0.5Magnesium salts Calcium0.5Calcium salts Iron0.2Iron salts

6 6 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

7 7 Make it, or eat it? 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.

8 8 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. Feast or famine: normal is what’s normal for you: Oligotrophs vs. copiotrophs

9 9 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

10 10 Endospore formation

11 11 Responses of microbes to other environmental stresses 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. ges/Betaine.gif

12 12 Culture Medium 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.

13 13 Componentgrams K2HPO40.10 KH2PO40.05 MgCl20.36 NaHCO30.05 {CaCl21 ml* {BaCl2.2H2O Na acetate0.01 FeCl.7H2O0.2 ml* RNA0.10 alanine0.15 arginine0.20 aspartic acid 0.30 glutamic acid0.55 glycine0.02 histidine0.20 isoleucine0.30 leucine0.20 lysine0.40 phenylalanine0.30 proline0.50 serine0.30 threonine0.50 valine0.30 Defined Medium for Cytophagas/Flexibacters

14 14 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!

15 15 Oxygen: friend or foe? 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.

16 16 Protections of bacteria against oxygen –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 Fe 2+ -SOD + O H+ → Fe 3+ -SOD + H 2 O 2

17 17 Relation to Oxygen Aerobes: use oxygen in metabolism; obligate. 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. A: aerobe B: microaerophile

18 18 Anaerobes grow without O 2 Classifications vary, but our definitions: –Obligate (strict) anaerobes: killed or inhibited by oxygen. –Aerotolerant anaerobes: do not use oxygen, but not killed by it. –Facultative anaerobes: can grow with or without oxygen C: could be facultative or aerotolerant. D: strict anaerobe


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