Chapter 7

 

Microbial Nutrition and Growth

 

 

Essential Nutrients

Macronutrients – essential for cell structure and metabolism

include Carbon, Oxygen, and Hydrogen

Micronutrients (trace elements) – involved in enzyme function

include nickel, zinc, and manganese

Growth factors – small molecules that cannot be produced by the cell

include vitamins and amino acids

Nutrients are used to synthesize amino acids, lipids, nucleic acids, ATP, and sugars

 

 

Sources of Nutrients: Carbon

Autotrophic - use inorganic carbon in the form of  carbon dioxide

convert CO2 in environment to an organic form

Heterotrophic - use organic carbon as energy source (glucose)

 

 

Sources of Nutrients: Energy

Phototrophic- harvest energy from sunlight (plants, algae)

Chemotrophic - obtain energy by metabolizing chemical compounds

Used by mammals, fungi, bacteria

 

 

Energy & Carbon Sources

Photoautotrophic

considered the primary producers

use the energy of sunlight and carbon in the atmosphere (CO2) to make organic compounds

photosynthetic organisms - algae, plants, and cyanobacteria

Chemoautotrophic

obtain energy from inorganic or organic compounds and carbon from CO2

Methanogens - methane-producing bacteria in ocean vents and hot springs

Photoheterotrophic

use organic carbon sources and light as energy source

purple and green bacteria

Chemoheterotrophic

majority of microbes

obtain carbon and energy from organic sources

 

 

Environmental Factors

 

Temperature

all microbes have 3 cardinal temperatures:

  minimum temperature

  maximum temperature

  optimal temperature

 

 

Temperature Classifications

Psychrophilic

optimal temp below 15 C

cannot grow above 20 C

found in frigid ocean waters

Psychrotrophic

optimal temp from 15–30 C

common cause of food spoilage

found in cool soil and water

Mesophilic

includes majority of medically important microbes

optimal temp of 20–40 C, human pathogens usually 30–40 C

found in soil, water, plants, and animals

Thermoduric - can withstand short periods of higher temp

Thermophilic

optimal temp from 45-80 C

found in hot springs, compost heaps, and water heaters

Hyperthermophilic

optimal temp from 80–121oC

usually Archaea found in hydrothermal vents in the ocean floor

 

 

Gas Requirements

Obligate aerobe

require O2 to survive

Micrococcus and Bacillus

Facultative anaerobe

grow best in presence of O2 but can survive without it

Escherichia and Staphylococcus

Obligate anaerobe

cannot survive in the presence of O2

inhabit oral cavity and large intestine

Microaerophile

require small amounts of O2 but larger amounts inhibit it

live in soil or water

Aerotolerant anaerobe

cannot use O2 but can survive in its presence

Lactobacillus and Streptococcus

Capnophile

grow best in high CO2 environments

Neisseria and Streptococcus

 

 

pH Requirements

Neutrophilic

prefer pH of 5–8; human pathogens usually 6.5–7.5

extremes in pH inhibit enzyme function

Acidophilic

grow best at pH below 5.5

found in acid mine waste and volcanic fissures

Alkalophilic

grow best at pH above 8.5

found in alkaline lakes and soils

 

 

Osmotic Pressure

Most microbes prefer hypotonic or isotonic environments

 

 

Osmotic Classifications

Halophilic

require high levels of NaCl (>9%) to grow (marine bacteria)

Facultative halophile

can survive up to 20% NaCl (Staphylococcus)

 

 

Microbial Associations

Symbiotic - organisms live together in a close partnership required by one or both members

Mutualism - Both members benefit

Commensalism- commensal benefits but the other member is not harmed

Parasitism - parasite benefits and host is usually harmed

Nonsymbiotic - organisms are free-living and do not require each other for survival

Synergism - members cooperate and share nutrients

   ex. Biofilms

Antagonism - some members are inhibited or destroyed by others

   ex. naturally occurring antibiotics

 

 

Bacterial Reproduction

Binary fission

Parent cell enlarges, duplicates its genetic material, and divides into 2 daughter cells

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

new cell wall forms between daughter cells

cells separate or remain attached forming chains (strepto), packets (sarcina), or clusters (staphylo)

 

 

Generation Time

Time necessary for a population to double in number by binary fission

average is 30-60 minutes

ranges from 5-10 min to 10-30 days

Population growth is exponential

2 4 8 16 32 64 128

Population size can be calculated

Nf = (Ni)2n

  Nf = final number of cells

  Ni = starting number of cells

  n = number of generations

 

 

Bacterial Growth Curve

Shows the predictable pattern of bacterial growth in closed system

Lag phase

slow or no growth

cells are producing the molecules necessary for growth

Log (exponential) phase

optimal growth and reproduction

most susceptible to antibiotics

Stationary phase

cell growth slows

cell death balances out cell reproduction

caused by:

  decreased nutrients

  accumulated wastes

  increased cell density

Death phase

cell death outpaces cell reproduction

caused by depletion of nutrients

99% of viable cells die

Phase of prolonged decline

the fittest cells can survive on nutrients released by dying cells

can last for months to years

generates slightly modified populations