Chapter 7 – Microbial Nutrition, Ecology and Growth
I.
Microbial Nutrition
Nutrition - process of acquiring nutrients from the environment and using them for metabolism and
growth
Definitions
1. essential nutrient – cannot be made by the cell – must be obtained from the
environment
2. macronutrient – required in large amounts (C,H,O)
3. micronutrient – required in small amounts ( e.g., trace elements) – Mn, Z, Ni, Co, Cu
4. inorganic nutrients – simple molecule composed of atoms other than C
and H; e.g., metals, salts, gases, water
some microbes can live entirely on inorganic substances
5. organic nutrients – contain C and H – usually the products of other living things;
methane, carbohydrates, lipids, proteins, nucleic acids
The Microbial Cytoplasm – Table 7.2
1. Water – 70%
2. Most of the dry weight comes from organic molecules (proteins are the most abundant)
3. 96% of cell is composed of only 6 elements – C H O N P S
Sources of Nutrients
1. Carbon
 Heterotrophs – need organic carbon sources
o Proteins, carbohydrates, lipids, nucleic acids

Autotrophs – use inorganic carbon source ( usu. CO2) to create organic
carbon compounds
o Not nutritionally dependent on other living organisms
2. Nitrogen - used to make amino acids and proteins

Sources: N2 gas; ammonium ions (NH4+), nitrates (NO3-) , nitrites

nitrogen fixation –microbes fix N2 into organic compounds like nitrates or
ammonia that can be used by other organisms to build amino acids and
proteins.
3. Oxygen – used for cell respiration and redox reactions
4. Hydrogen
 Maintains pH and forms H-bonds between molecules
5. Phosphorous (Phosphate)
 Come from nucleic acids, phospholipids, ATP, coenzymes – and used to build
those same molecules
 Some bacteria can get phosphate from Inorganic sources such as – rocks,
oceanic material, mineral deposits
6. Sulfur
 Used for amino acids and vitamin (B 1) synthesis
 sources: sulfates (SO42-) - rocks, sediments; H2S ; some amino acids
Miscellaneous Nutrients
1. Mineral Ions
 K+ - protein synthesis; membrane function
 NA+ - cell transport
 Ca++ - stabilizes the cell wall; endospore formation
 Mg++ -- used to make chlorophyll; needed for the membrane & ribosomes
 Z - for regulation of DNA
2. Trace elements – Cu, Co, Ni, Mb, Mn, Si, B, I,
 Some trace elements (like iron) encourage bacterial growth – other types of metal
ions can be toxic to bacteria
3. Growth Factors
 essential organic compounds ( organism can’t make these)
 must be obtained from the environment
 vitamins; amino acids; purines & pyrimidines
Nutritional Types - All organisms need a carbon source and an energy source
Carbon Source
 Heterotrophs – need organic carbon source ( usu. Glucose)
 Autotrophs – use inorganic carbon source ( usu. CO2) to create organic
carbon compounds
Energy Source
 Photo - use light as an energy source
 Chemo – use chemical energy source
1. Autotrophs
Photoautotrophs
 Photosynthetic
 Light energy  converted to chemical energy
 Inorganic carbon ( CO2 )  organic carbon
 Primary producers ( algae, plants, cyanobacteria) – basis of food webs
Chemoautotrophs
 Chemical energy – can be organic or inorganic
 Inorganic Carbon - ( CO2 )
 Bacteria and Archaea - lithoautotrophs (deep sea vents), methanogens (
Archaea)
2. Heterotrophs
Photoheterotrophs
 The purple and green photosynthetic bacteria
 Light energy
 Organic Carbon source
Chemoheterotrophs
 The majority of heterotrophs
 Glucose or other organic compounds are used for both a chemical energy
and a Carbon source
Saprobes –
 decomposers – feed on dead organic matter such as plant litter, dead
animal matter, dead microbes
 important to the environment
 bacteria and fungi
Parasites
 Live on or in the body of the host - Parasite benefits ; host is harmed
 Parasites are pathogens ( damage tissues, cause disease)
 Viruses, bacteria, fungi, protozoa, worms
3. Extremophiles – See Insight 7.1, 7.2, 7.3
II.
Transport Across the Membrane
Osmosis –
 The movement of water from an area of higher concentration to an area of lower concentration
across a semipermeable membrane
 Aqueous solutions – water is the solvent; dissolved solids = solute
 Isotonic – term applied to solutions that have identical concentrations of solute
 Hypertonic – When comparing two solutions, the term applied to the solution with the greater
solute concentration
 Hypotonic – When comparing two solutions, the term applied to the solution with the lesser
solute concentration
 Cells in a Hypotonic solution – water moves into cell
o Cell becomes swollen or turgid ; it may lyse;
o Intact cell walls help protect against lysis from osmotic pressure
 Cells in a Hypertonic solution – Lose water – shrink (plasmolyse) ; Halophilic bacteria can
live in very high salt environments
 Cells in an Isotonic solution – water gains equal water loss ; no net change
Passive Transport
 Molecules move from area of higher concentration to area of lower concentration – “down
the concentration gradient”
 No ATP ( energy) is spent by the cell




Simple Diffusion
Movement from area of higher concentration to lower concentration
Continues until movement in both directions is equal (Equilibrium )
Oxygen, CO2 and other gases; small non-polar or lipid molecules




Facilitated diffusion
Transported substance binds to a carrier protein
Specificity – carrier proteins bind and transport only a single type of molecule
Competition – two competing molecules of similar shape may bind on the transport protein –
One is usually transported in preference to the other
Glucose, amino acids, DNA bases, sugars

Active Transport
 Moves “against” or “up” the concentration gradient ( from an area of lower concentration to
an area of higher concentration)
 Requires energy (usually ATP) and requires a carrier protein
 Cell can use this to concentrate nutrients inside - Monosaccharides, amino acids,
phosphates, metal ions
 Na + / K+ - ATP pump
Bulk transport – Endocytosis – See Fig 7.7 for Process
 bulk transport of large molecules, particles or liquids across the membrane
 these substances do not pass through the membrane
1. Phagocytosis
o
Ingestion of solid particles or whole cells
o
Cell membrane extends and engulfs the particle; enters the cell in a vacuole;
digested inside the cell
o
Done by - Amoebas, macrophages, WBCs
2. Pinocytosis
o
Liquids – e.g., oils or molecules in solution enter through pinocytosis
o
Projections from the membrane called microvilli surround the fluid – bring it into the
cell in a vesicle.
III.
Environmental Factors that Influence Microbes
A. Temperature
1. Range – maximum, minimum, optimum
2. Classification by Temperature
Psychrophiles – optimal <150C ; oceans, Arctic ice, snowfields
Psychrotrophs – optimal ~ 20-300C ; food spoilage in refrigerators
Mesophiles – optimal 20-40 0C

Most common type of microbe

Causes most food spoilage

Found in animals, temperate, tropical or subtropical soils and water

Most likely to cause human disease

Thermodurics – can withstand short bursts of high temperatures – spoil
food and cause disease ( heat-resistant cysts and endospores)
Thermophiles – optimal 50-60 0C

Hot water; sunny soil; hot springs; compost piles
Hyperthermophiles – optimal > 800C

Volcanic hot springs ; deep sea hydrothermal vents

Sulfur bacteria

Highest known temperature for growth ( 80 - 1200C)

Enzymes used for biotechnology – See Insight 7.4
B. Oxygen
Toxic Forms of Oxygen – usually need to be converted to water

Singlet oxygen – highly reactive, high energy form

Superoxide -- highly toxic; strips electrons from molecules
o Superoxide dismutase (SOD) will convert this to O2 and peroxide
o All organisms that grow in air need SOD

Hydrogen Peroxide – ( H2O2) -- also highly toxic
o Catalase – converts hydrogen peroxide into water and oxygen (
bubbles)
o Peroxidase – converts hydrogen peroxide into water

Hydroxyl Radical – the most reactive form; formed by ionizing radiation
Classification by Oxygen Requirement

Obligate aerobes – require O2 ; have SOD and catalase

Facultative anaerobes – can use O2 if present; can switch to anaerobic respiration
or fermentation if no O2 is present; usu. have SOD and catalase

Obligate anaerobes – can’t use O2 ; poisoned by O2 ( e.g., Clostridium spp.)
Don’t produce either SOD or catalase; found in deep muds, lakes,
oceans, oral cavity, intestine

Aerotolerant anaerobe – can tolerate O2, but don’t use it for growth

Microaerophile - require O2, but only in low concentrations
Anaerobic Growth Media & Methods for Culturing Anaerobes
 anaerobic organisms are killed by exposure to oxygen


Reducing media
o contain ingredients that chemically combine with the oxygen in the
media ( remove it) – e.g., thioglycollate broth
o usually contain an oxygen indicator ( resazurin or methylene blue)
Anaerobic jars - for culture plates – see fig 7.10
o Chemical packet + water  oxygen is consumed; H and CO2 are
produced
o Jar must be tightly sealed
o Oxygen indicator strip ( resazurin or methylene blue)
Capnophiles – require high concentrations of CO2 – use candle jars or bags ; incubate at
increased concentrations of CO2

Neisseria ( cause gonorrhoea, meningitis) ; Streptococcus pneumoniae;
Brucella ( causes undulant fever or Brucellosis)
C. PH
 best range ( 6 – 8)
 below 4 – too acid for most bacteria ( acid foods are preserved); acidophiles are “acidloving” bacteria
 molds and yeast tolerate moderate acid pH – spoil acid-preserved foods
 alkalinophiles – hot pools and soils – pH up to 10
 buffers – added to growth media
D. Osmotic Pressure ( Fig. 7.4)
 Cells require water ; nutrients are obtained in solution; cells are about 80-90% water
 Isotonic – normal cell function
 Hypertonic - plasmolysis inhibits growth
 Hypotonic - cell swells; will lyse if cell wall is weak; osmotic lysis
 Food preservation – high salt; high sugar
 Halophiles – “salt-loving” bacteria ; some tolerate salt; some require salt – Staphylococcus
is a facultative halophile
E. Miscellaneous Environmental Factors
 Pigments - protect against damaging effects of light or UV radiation
 Barophiles - deep-sea microbes – adapted to live under high pressure
 Dehydrated cells - spores and cysts – resist drying out
F. Ecological Associations Among Microorganisms
Symbiotic – Organisms live in a close nutritional relationship

Mutualism – Insight 7.5;

Commensalism ; Fig 7.12

Parasitism
Non-Symbiotic – relationships are not required for survival
 Synergism
o Mixed infections – gum disease, gas gangrene, dental caries
o Bacteria and plant roots
 Antagonism
o Antibiosis – antibiotics and bacteriocins
G. Interrelationships Between Microbes and Humans
1. normal microbial flora – e.g., E.coli, Lactobacillus
H. Special Culture Techniques
1. Growth in live animals - e.g., Mycobacterium leprae / armadillos
2. Treponema pallidum – the syphilis spirochete ; cannot grow on artificial media
3. Rickettsia, chlamydiae – intracellular bacteria – grown in live cell culture
4. Viruses – must be grown in live cell culture
IV.
Growth of Bacterial Cultures
Binary Fission – bacterial cell division
The Rate of Population Growth
1. Generation Time – time required for a cell to divide ( = population doubling time)
Logarithmic (Exponential) Growth – population doubles with every generation
1. 1 cell  2 cells  4  8  16  32  64  128  256, etc.
2. graph log of the population = straight line graph
Typical Bacterial Growth Curve ( Phases of Growth)
1. Lag Phase – little or no cell division;
metabolic activity increasing to prepare for cell division
2. Log Phase – growth or logarithmic increase in numbers
reproduction is greatest;
most metabolically active stage;
most sensitive to drugs, poisons, radiation, etc.
3. Stationary Phase – metabolic activity slows; # deaths = # new cells
4. Death Phase (logarithmic decline ) -- # of deaths > # new cells
II.
Measurement of Microbial Growth
Direct Measurement – counts the # cells / ml. of sample
1. Plate Counts – Pour Plate or Spread Plates

if bacteria are present in large numbers – count very small sample OR make a serial
dilution

Serial dilutions – dilute by a series ( usu. Factors of 10)

Plate specimen & incubate

Count colonies ( choose plate with 25-250 colonies)

Multiply by dilution factor to get # cells / ml. of sample

Advantage - Only counts viable cells

Disadvantage – errors in making dilutions occur; takes time to form colonies
2.
Direct Microscopic Cell Count

use ruled counting chamber; multiply by dilution factor

Disadvantage – counts dead & live cells; hard to count motile bacteria; only good when
bacterial numbers are high

Advantage – no incubation time; can be done by electronic instrument
3. Other Methods – Coulter counter(Fig 7-18) ; flow cytometer, real time PCR
Indirect Measurements
1. Turbidity – As bacteria multiply, the medium becomes turbid ; can be read on the
spectrophotometer; % of light transmitted decreases as bacterial numbers (tubidity increase)