Chapter 7

Chapter 7

Chapter 7 Microbial Nutrition, Ecology, and Growth Microbial Nutrition 7.1 Microbial Nutrition A. Nutrition: a process by which chemical substances (nutrients) are acquired from the environment and used in cellular activities

1. All living things require a source of elements such as C, H, O, P, N, and S A) K, Ca, Fe, Na, Cl, and Mg are usually needed but the relative amounts vary depending on the microbe Microbial Nutrition 2. Essential Nutrient: any substances that must be provided to an organism

3. Macronutrients: Required in relatively large quantities, play principal roles in cell structure and metabolism (ex. C, H, O) 4. Micronutrients: aka trace elements, present in smaller amounts and involved in enzyme function and maintenance of protein structure (ex. Mn, Zn, Ni) Microbial Nutrition B. Carbon Sources

1. Required for producing nearly all cell components 2. Heterotrophs must obtain C from organic sources 3. Autotrophs use inorganic CO 2 as their carbon source C. Nitrogen Sources 1. Necessary for the production of DNA, RNA, ATP, and amino acids

Microbial Nutrition 2. Primary nitrogen source for heterotrophs proteins, DNA, RNA, and amino acids 3. Some bacteria and algae utilize inorganic nitrogenous nutrients 4. Small number can transform N2 into usable compounds through nitrogen fixation A) Regardless of the initial form, must be converted to NH3 before cells can use it

Microbial Nutrition D. Oxygen Sources 1. Necessary for biomolecule production and ATP synthesis 2. Can be obtained from both organic and inorganic sources E. Hydrogen Sources 1. Necessary for: A) Maintaining pH

Microbial Nutrition B) Forming hydrogen bonds C) Serving as the source of energy in oxidation-reduction reactions D) Production of all biomolecules 2. May be obtained from any Hcontaining molecules Microbial Nutrition F. Phosphorus (Phosphate) Sources

1. Necessary for the production of DNA, RNA, ATP, and phospholipids A) Primarily obtained form these sources 2. Some bacteria can obtain it from inorganic sources A) PO4-3 (phosphate ions) and multiple forms of HPO4 (hydrogen phosphate) in rocks and ocean mineral deposits Microbial Nutrition

G. Sulfur Sources 1. Necessary for the production of select amino acids and is vital for tertiary protein structure 2. Obtained by consuming sulfurcontaining organic molecules (amino acids) 3. Also found in rock and sediment deposits often as SO4 (sulfate) Microbial Nutrition

H. Other Nutrients Important in Microbial Metabolism 1. Most organisms also require K, Na, Ca, Mg, Fe, and Zn in smaller amounts 2. A small number require Cu, Co, Ni, Mn, I, and B Microbial Nutrition I. Growth Factors: Essential Organic Nutrients

1. Growth factor: An organic compound that cannot be synthesized by an organism and must be provided as a nutrient 2. Examples include some amino acids, fatty acids, and vitamins Nutritional Classifications J. Main Determinants of Nutritional Type 1. Sources of carbon and energy

A) Phototrophs microbes that photosynthesize B) Chemotrophs microbes that gain energy from chemical compounds Nutritional Classifications 2. Autotrophs and Their Energy Sources A) Photoautotrophs 1) Photosynthetic 2) Considered the primary producers

on the planet 3) Cyanobacteria are the primary example Nutritional Classifications B) Chemoautotrophs 1) Chemoorganic autotrophs use organic compounds for energy and inorganic compounds as a carbon source

2) Lithoautotrophs rely totally on inorganic minerals a) Methanogens produce methane from hydrogen gas and carbon dioxide Nutritional Classifications 3. Heterotrophs and Their Energy Sources A) Majority are chemoheterotrophs that

derive both carbon and energy from organic compounds B) Saprobes 1) Free-living microorganisms 2) Feed primarily on organic material from dead organisms Nutritional Classifications a) Decomposers of plant litter, animal matter, and dead microbes

b) Considered the primary decomposers on the planet c) Most have rigid cell wall, so they release enzymes to the extracellular environment and digest food particles into smaller molecules Nutritional Classifications d) Obligate saprobes exist strictly on dead organic matter in soil and water

e) Facultative parasite when a saprobe infects a host, usually when the host is compromised (opportunistic pathogen) Nutritional Classifications C) Other Chemoheterotrophs 1) Parasites a) Derive nutrients from the cells or tissues of a living host b) Also called pathogens because

they cause damage to tissues or even death Nutritional Classifications c) 3 basic classifications i) Ectoparasites live on the body ii) Endoparasites live in organs and tissues iii) Intracellular parasites live within cells

d) Obligate parasites unable to grow outside of a living host Environmental Classifications 7.2 Environmental Factors that Influence Microbes A. Temperature Adaptations 1. All microbes have 3 critical temps A) Minimum temperature

B) Maximum temperature C) Optimal temperature Environmental Classifications 2. Classifications A) Psychrophilic 1) Optimal temp between -515oC 2) Cannot grow above 20oC 3) Found in frigid ocean waters

Environmental Classifications B) Psychrotrophic 1) Optimal temp from 2030oC 2) Common cause of food spoilage 3) Found in cool soil and water Environmental Classifications

C) Mesophilic 1) Accounts for vast majority of medically important microbes 2) Optimal temp of 2040oC a) Human pathogens usually 3040oC 3) Found in soil, water, plants and animals 4) Some can withstand short periods of higher temp = thermoduric

Environmental Classifications D) Thermophilic 1) Optimal temps above 45oC a) Usually 4580oC 2) Some can survive up to 100oC a) Temp at which most enzymes are destroyed 3) Found in hot springs, compost heaps and water heaters

Environmental Classifications E) Hyperthermophilic 1) Optimal temp from 80120oC 2) Usually Archaea 3) Found in hydrothermal vents in the ocean floor a) A newly discovered bacteria can survive up to 130oC

Environmental Classifications B. Gas Requirements 1. Several General Categories of Oxygen Requirements A) Aerobe can use gaseous oxygen in its metabolism and possesses the enzymes needed to process toxic oxygen products

1) Obligate (strict) aerobe cannot grow without oxygen Environmental Classifications 2) Facultative anaerobe an aerobe that does not require oxygen for its metabolism and is capable of growth in the absence of it 3) Microaerophile does not grow at

normal atmospheric concentrations of oxygen but requires a small amount of it in metabolism Environmental Classifications B) Anaerobe lacks the metabolic enzyme systems for using oxygen in respiration 1) Obligate (strict) anaerobes also lack the enzymes for processing toxic oxygen and

cannot tolerate any free oxygen in the immediate environment and will die if exposed to it 2) Aerotolerant anaerobes do not utilize oxygen but can survive and grow to a limited extent in its presence Environmental Classifications C) Carbon Dioxide

1) Capnophiles grow best at higher CO2 levels than are normally present in the atmosphere Environmental Classifications C. Effects of pH 1. Neutrophilic A) Prefer pH of 58 1) Human pathogens usually 6.57.5

B) Dont grow well in extremes 1) Inhibits enzyme function Environmental Classifications 2. Acidophilic A) Grow best at pH below 5.5 B) Ex. Helicobacter & Lactobacillus 3. Alkalophilic A) Grow best at pH above 8.5

B) Found in alkaline lakes and soils Environmental Classifications D. Osmotic Pressure 1. Most microbes live either under hypotonic or isotonic conditions 2. 2 main classifications A) Facultative halophile 1) Dont normally reside in high-salt

environments but some can survive up to 20% NaCl 2) Ex. Staphylococcus Environmental Classifications B) Obligate (strict) halophile 1) Requires at least 9% NaCl but optimal is ~25%

Microbial Growth 7.3 The Study of Microbial Growth A. The Basis of Population Growth: Binary Fission 1. Process A) Parent cell enlarges and duplicates all its genetic material Microbial Growth B) DNA copies move to opposite ends of

parent and attach to a section of the cell membrane as it begins to pinch together at the center C) New cell wall forms between daughter cells D) Cells separate or may remain attached forming chains/clusters Figure 7.13

Microbial Growth B. The Rate of Population Growth 1. Generation time: The time required for a complete fission cycle 2. Average is 30-60 minutes A) Ranges from 10-12 min to 10-30 days B) Most food-borne pathogens take 20-30 min

Microbial Growth C. Bacterial Growth 1. Bacterial growth is exponential A) 2 4 8 16 32 64 128 2. To calculate the size of a population over time: Nf = (Ni)2n A) Nf = is the final number of cells B) Ni = is the starting number C) n = denotes the generation number

Microbial Growth D. The Population Growth Curve 1. A population of bacteria does not maintain its potential growth rate and double endlessly 2. A population displays a predictable pattern called a growth curve 3. Data from an entire growth period typically produce a curve with a series of phases

Microbial Growth 4. 5 phases A) Lag phase 1) Period of slow or no growth 2) Cells are producing the molecules necessary for growth B) Log (exponential) phase 1) Period of optimal growth and reproduction

2) Will continue as long as there are sufficient nutrients and space Microbial Growth C) Stationary phase 1) Cell death balances out cell reproduction 2) Caused by: a) Decreased nutrients b) Accumulated wastes

c) Increased cell density Microbial Growth D) Death phase 1) Cell death outpaces cell reproduction 2) Caused by depletion of nutrients 3) 99% of viable cells die E) Phase of prolonged decline 1) The fittest cells can survive on the nutrients released by dying cells

2) Can last for months to years

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