Post on 21-Jan-2016
Chapter 6
Microbial Growth
© 2013 Pearson Education, Inc. Lectures prepared by Christine L. Case
The Requirements for Growth
• Physical requirements– Temperature– pH– Osmotic pressure
• Chemical requirements– Carbon– Nitrogen, sulfur, and phosphorous– Trace elements– Oxygen– Organic growth factor
Figure 6.1 Typical growth rates of different types of microorganisms in response to temperature.
PsychrophilesPsychrotrophs
Mesophiles
Thermophiles
Hyperthermophiles
Applications of Microbiology 6.1 A white microbial biofilm is visible on this deep-sea hydrothermal vent. Water is being emitted through the ocean floor at temperatures above 100°C.
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
Osmotic Pressure
• Hypertonic environments, or an increase in salt or sugar, cause plasmolysis
• Extreme or obligate halophiles require high osmotic pressure
• Facultative halophiles tolerate high osmotic pressure
Figure 6.4 Plasmolysis.
Plasma membraneCell wall
Cytoplasm
H2O
NaCl 10%
Cytoplasm
Plasma membrane
Cell in isotonic solution. Plasmolyzed cell in hypertonic solution.
NaCl 0.85%
Chemical Requirements
• Carbon– Structural organic molecules, energy source– Chemoheterotrophs use organic carbon sources– Autotrophs use CO2
Chemical Requirements
• Nitrogen– In amino acids and proteins– Most bacteria decompose proteins– Some bacteria use NH4
+ or NO3–
– A few bacteria use N2 in nitrogen fixation
Chemical Requirements
• Sulfur– In amino acids, thiamine, and biotin– Most bacteria decompose proteins– Some bacteria use SO4
2– or H2S
• Phosphorus – In DNA, RNA, ATP, and membranes– PO4
3– is a source of phosphorus
Chemical Requirements
• Trace elements– Inorganic elements required in small amounts– Usually as enzyme cofactors
Table 6.1 The Effect of Oxygen on the Growth of Various Types of Bacteria
Organic Growth Factors
• Organic compounds obtained from the environment
• Vitamins, amino acids, purines, and pyrimidines
Biofilms
• Microbial communities• Share nutrients• Sheltered from harmful factors
Figure 6.5 Biofilms.
Clumps of bacteria adhering to surface
Surface Water currents
Migrating clump of bacteria
Applications of Microbiology 3.2 Pseudomonas aeruginosa biofilm.
© 2013 Pearson Education, Inc.
Culture Media
• Culture medium: nutrients prepared for microbial growth
• Sterile: no living microbes• Inoculum: introduction of microbes into
medium• Culture: microbes growing in/on culture
medium
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
Table 6.2 A Chemically Defined Medium for Growing a Typical Chemoheterotroph, Such as Escherichia coli
Table 6.4 Composition of Nutrient Agar, a Complex Medium for the Growth of Heterotrophic Bacteria
Anaerobic Culture Methods
• Reducing media– Contain chemicals (thioglycolate or oxyrase) that
combine O2
– Heated to drive off O2
Figure 6.6 A jar for cultivating anaerobic bacteria on Petri plates.
Lid with O-ring gasket
Envelope containing sodium bicarbonate and sodium borohydride
Anaerobic indicator (methylene blue)
Petri plates
Clamp with clamp screw
Palladium catalyst pellets
Figure 6.7 An anaerobic chamber.
Arm ports
Air lock
Capnophiles
• Microbes that require high CO2 conditions
• CO2 packet
• Candle jar
• Make it easy to distinguish colonies of different microbes
Differential Media
Figure 6.9 Blood agar, a differential medium containing red blood cells.
Bacterial colonies
Hemolysis
Figure 6.10 Differential medium.
Uninoculated
Staphylococcusepidermis
Staphylococcusaureus
• Suppress unwanted microbes and encourage desired microbes
Selective Media
Table 6.5 Culture Media
• Binary fission• Budding• Conidiospores (actinomycetes)• Fragmentation of filaments
ANIMATION Bacterial Growth: Overview
Reproduction in Prokaryotes
Figure 6.12a Binary fission in bacteria.
Cell elongates and DNA is replicated.
Cell wall and plasma membrane begin to constrict.
Cross-wall forms, completely separating the two DNA copies.
Cells separate.
Cell wall
Plasma membrane
DNA (nucleoid)
(a) A diagram of the sequence of cell division
Figure 6.12b Binary fission in bacteria.
(b) A thin section of a cell of Bacillus licheniformis starting to divide
Cell wallDNA (nucleoid)
Partially formed cross-wall
© 2013 Pearson Education, Inc.
Figure 6.13b Cell division.
Lag PhaseIntense activity preparing for population growth, but no increase in population.
Log PhaseLogarithmic, or exponential, increase in population.
Stationary PhasePeriod of equilibrium; microbial deaths balance production of new cells.
Death PhasePopulation Is decreasing at a logarithmic rate.
The logarithmic growth in the log phase is due to reproduction by binary fission (bacteria) or mitosis (yeast).
Figure 6.15 Understanding the Bacterial Growth Curve.
Staphylococcus spp.