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


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


obtain energy from inorganic or organic compounds and carbon from CO2

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


use organic carbon sources and light as energy source

purple and green bacteria


majority of microbes

obtain carbon and energy from organic sources



Environmental Factors



all microbes have 3 cardinal temperatures:

minimum temperature

maximum temperature

optimal temperature



Temperature Classifications


optimal temp below 15 C

cannot grow above 20 C

found in frigid ocean waters


optimal temp from 15–30 C

common cause of food spoilage

found in cool soil and water


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


optimal temp from 45-80 C

found in hot springs, compost heaps, and water heaters


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


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


grow best in high CO2 environments

Neisseria and Streptococcus



pH Requirements


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

extremes in pH inhibit enzyme function


grow best at pH below 5.5

found in acid mine waste and volcanic fissures


grow best at pH above 8.5

found in alkaline lakes and soils



Osmotic Pressure

Osmosis – diffusion of water through a selectively permeable membrane

Hypertonic – high salt environment

Causes cells to lose water and shrink

Hypotonic – low salt environment

Causes water to enter the cell

Cell walls protect, but those without walls can burst

Isotonic – same salt environment

Preferred by most microbes



Osmotic Classifications


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

99% of viable cells die - the fittest cells can survive on nutrients released   by dying cells

Can last for weeks to months

Refrigeration can slow death