1Bacterial Growth and Nutrition

• Bacterial nutrition and culture media• Chemical and physical factors affecting growth• The nature of bacterial growth• Methods for measuring population size

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2The First Law of Thermodynamics

• Matter cannot be created or destroyed.– It is interchangeable with energy.– Einstein’s famous equation: E = mc2

• 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 in raw materials, only

use it to assemble raw materials.– Bacteria can’t grow on nothing!

3Where 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.

4Essentials of Bacterial nutrition• Six elements needed in large quantities by all living

things: CHONPS– Carbon, hydrogen, oxygen, nitrogen, phosphorous,

and sulfur. H and O are common. Sources of C, N, P, and S must also be provided.

• Other macronutrients: not as much needed:– Mineral salts such as Ca+2, Fe+3, Mg+2, K+

• Micronutrients = trace elements; needed in very tiny amounts: things like Zn+2, Mo+2, Mn+2

• Elements must be in the correct chemical form!– Diamonds, graphite no good. N2 used by very few

bacteria.

5Element % dry wgt Source

Carbon 50 organic compounds or CO2

Oxygen 20 H2O, organic compounds, CO2, and O2

Nitrogen 14 NH3, NO3, organic compounds, N2

Hydrogen 8 H2O, organic compounds, H2

Phosphorus 3 inorganic phosphates (PO4)

Sulfur 1SO4, H2S, 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

6Make 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, 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.

7Responses of microbes to nutritional deficiency

• Siderophores, hemolysins, and extracellular enzymes– Collect iron, other nutrients.

• 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.– Bacteria form spores for survival

• Fungi form spores for reproduction

8Endospore formation

http://www.microbe.org/art/endospore_cycle.jpg

9Culture 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.

10

Component gramsK2HPO4 0.10KH2PO4 0.05MgCl2 0.36NaHCO3 0.05{CaCl2 1 ml*{BaCl2.2H2ONa acetate 0.01FeCl.7H2O 0.2 ml* RNA 0.10 alanine 0.15arginine 0.20aspartic acid 0.30glutamic acid 0.55

glycine 0.02histidine 0.20isoleucine 0.30leucine 0.20lysine 0.40phenylalanine 0.30proline 0.50serine 0.30threonine 0.50valine 0.30

Defined Medium for Cytophagas/Flexibacters

11Physical requirements for growth

• Prefixes and suffixes:

• Bacteria require wide ranges of conditions– Optimal conditions implied by “-phile”

meaning “love”

• Some bacteria prefer other conditions, but can tolerate extremes– Suffix “-tolerant”

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12Oxygen: 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, H2O2(peroxide), O3

- (superoxide), and hydroxyl (OH-) radical.

13Protections 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.

14Relation to Oxygen

• Aerobes: use oxygen in metabolism; obligate.

• Anaerobes: grow without oxygen; SEE BELOW

• Microaerophiles: require oxygen, but in small amounts.

• Capnophiles: require larger amounts of carbon dioxide.

Classifications vary, but our definitions: Obligate 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

15Effect of temperature

• Low temperature– Enzymatic reactions too slow; enzymes too stiff– Lipid membranes no longer fluid

• High temperature– Enzymes denature, lose shape and stop functioning– Lipid membranes get too fluid, leak– DNA denatures

• As temperature increases, reactions and growth rate speed up; at max, critical enzymes denature.

16Bacteria and temperature

• Bacteria have temperature ranges (grow between 2 temperature extremes), and an optimal growth temperature. Both are used to classify bacteria.

• As temperature increases, so do metabolic rates.• At high end of range, critical enzymes begin to

denature, work slower. Growth rate drops off rapidly with small increase in temperature.

17Classification of bacteria based on temperature

18Terms related to temperature

• Special cases:– Psychrotrophs: bacteria that grow at “normal”

temperature ranges (e.g. room temperature” but can also grow in the refrigerator; responsible for food spoilage.

– Thermoduric: more to do with survival than growth; bacteria that can withstand brief heat treatments.

19pH Effects

• pH = -log[H+]

• Lowest = 0 (very acid); highest = 14 (very basic) Neutral is pH 7.

• Acidophiles/acidotolerant grow at low pH

• Alkalophiles/alkalotolerant grow at high pH

• Most bacteria prefer a neutral pH– What is pH of human blood?

• Some bacteria create their preferred conditions– Lactobacillus creates low pH environment in vagina

20Low water activity:halophiles, osmophiles, and xerotolerant

• Water is critical for life; remove some, and things can’t grow. (food preservation: jerky, etc.)

• Halophiles/halotolerant: relationship to high salt.– Marine bacteria; archaea and really high salt.

• Osmophiles: can stand hypertonic environments whether salt, sugar, or other dissolved solutes– Fungi very good at this; grandma’s wax over jelly.

• Xerotolerant: dry. Subject to dessication. Fungi best– Bread, dry rot of wood– Survival of bacterial endospores.

21Miscellaneous conditions

• Radiation (solar, UV, gamma)– Can all damage cells; bacteria have pigments to

absorb energy and protect themselves.– Endospores are radiation resistant.– Deinococcus radiodurans: extremely radiation

resistant• Extremely efficient DNA repair, protection against

dessication damage to DNA.

• Barophiles/barotolerant: microbes from deep sea

– Baro- means pressure. Actually require high pressure as found in their environment.