2 - Metabolism and Growth

Copyright © 2010 Pearson Education, Inc.
Metabolism and Growth

Requirements for Growth: chemical
 NOT COPS
 N
 Organic growth factors
 Trace elements
 C
 O
 P
 S

What is the function of carbon,
nitrogen, sulfur, phosphorus and trace
elements?

Chemical Requirements
 Carbon
 Structural organic molecules, energy source
 Chemoheterotrophs use organic carbon sources
 Autotrophs use CO2

 Nitrogen
 In amino acids and proteins
 Most bacteria decompose proteins
 Some bacteria use NH4+ or NO3–
 A few bacteria use N2 in nitrogen fixation

 Sulfur
 In BAT: Biotin, amino acids, and protein
 Phosphorus
 In DNA, RNA, ATP, and membranes

 Trace elements
 Inorganic elements required in small amounts
 Usually as enzyme cofactors

Copyright © 2010 Pearson Education, Inc. Table 6.1
The Effect of Oxygen (O2) on Growth

Organic Growth Factors
 Where are organic growth factors obtained?
 from the environment
 What are organic growth factors involved with?
 Vitamins, amino acids, purines, and pyrimidines

Catabolic and Anabolic Reactions
 Metabolism: The sum of the chemical reactions in
an organism
 catabolism, require water: cells break down sugars
 anabolism, dehydration synthesis: formation of
proteins from amino acids

Catabolic and Anabolic Reactions
 A metabolic pathway is a sequence of
enzymatically catalyzed chemical reactions in a cell
 A - B, B - C, C - D
 A cannot make D
 Metabolic pathways are determined by enzymes
 Enzymes are encoded by genes

Enzymes
 Proteins
 Biological catalysts
 Produced by living cells
 Catalyze chemical reactions by lowering activation
energy
 Speed up a chemical reaction without being
permanently altered

Enzyme Components
 Biological catalysts
 Speed up a chemical reaction without being altered
 Are specific (active site) – act on specific substance
(substrate)
 Crucial function: speed up biochemical reactions at a temp
which is compatible with a living, normal functioning cell

Factors influencing Enzymatic Activity
 Temperature
 pH
 Substrate concentration
 Inhibitors

Inhibitors
Function: control bacteria by control of enzymes
 Competitive – compete with the normal substrate for
the active site
 shape and chemical structure are similar to normal
substrate
 Ex. Sulfa drug
 Noncompetitive – interact with another part of the
enzyme, changes shape = nonfunctional

Carbohydrate Catabolism
 The breakdown of carbohydrates to release energy
 Glucose most commonly used carbohydrate
 Glycolysis: breaking down glucose to pyruvic
acid

Carbohydrate Catabolism
 Glycolysis: glucose broken down
 Leads into cellular respiration (aerobic/anaerobic)
or fermentation
Aerobic Anaerobic Fermentation
Krebs cycle: high
energy
Part of Krebs
cycle: low energy
No Krebs
Electron transport
chain
Electron
Transport chain
No ETC
Final Acceptor:
O2
Final acceptor:
does not use O2
Various organic
end products
Inorganic product

Metabolic Diversity among Organisms
 Photoautotrophs
 Photoheterotrophs
 Chemoautotrophs
 Chemoheterotrophs
 Autotrophs – fix carbon
 Heterotrophs – cannot fix carbon
 Chemotrophs – energy from oxidation
 Phototrophs – energy from light

The Requirements for Growth: Physical
 Physical requirements
 Temperature
 pH
 Osmotic pressure

Physical Requirements
 Temperature
 Minimum growth temperature
 Optimum growth temperature
 Maximum growth temperature

Temperature
 Three primary Groups
1.Psychrophiles – cold loving
2.Mesophiles – moderate
3.Thermophiles – heat loving

Copyright © 2010 Pearson Education, Inc. Figure 6.1
Typical Growth Rates and Temperature

Psychrotrophs
 Grow between 0°C and 20–30°C
 Cause food spoilage

Food Preservation Temperatures

pH
 Most bacteria grow between pH 6.5 and 7.5
 Molds and yeasts grow between pH 5 and 6
 Acidophiles grow in acidic environments

Biofilms
 Microbial communities
 Form slime or
hydrogels
 Form on teeth, contact
lenses and catheters

Copyright © 2010 Pearson Education, Inc. Applications of Microbiology, p. 57
Biofilms
 Share nutrients
 Sheltered from
harmful factors
 70% bacterial
infections are
from biofilms
 100X more
resistant to
antibiotics than
free swimming
microbes

Agar
 Complex polysaccharide
 Used as solidifying agent for culture media in Petri
plates, slants, and deeps
 Generally not metabolized by microbes
 Liquefies at 100°C
 Solidifies at ~40°C

Culture Media
 Chemically defined media: Exact chemical
composition is known
 Complex media: Extracts and digests of yeasts,
meat, or plants
 Nutrient broth
 Nutrient agar

Anaerobic Culture Methods
 Reducing media
 Contain chemicals (thioglycolate or oxyrase) that combine
O2
 Heated to drive off O2
 Used to grow anaerobes

An Anaerobic Chamber

Selective Media
 Suppress unwanted microbes and encourage
desired microbes

Differential Media
 Make it easy to distinguish colonies of different
microbes.

The Streak Plate Method

Preserving Bacterial Cultures
 Deep-freezing: –50° to –95°C
 Lyophilization (freeze-drying): Frozen (–54° to –
72°C) and dehydrated in a vacuum

Measuring Microbial Growth
Direct Methods
 Plate counts
 Filtration
 MPN
 Direct microscopic count
Indirect Methods
 Turbidity
 Metabolic activity
 Dry weight

 Standard plate count
 Viable count
 Microscopic count
 No incubation time
 Growth phase gram + is suseptible to penic.
 LOG phase

2 - Metabolism and Growth

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