Chapter 6: Microbial Growth

Requirements for growth:

Requirements for growth:

Physical:
-temperature, pH, osmotic pressure
Chemical:
-CHONPS (macronutrients), trace elements, oxygen, growth factors

in hypertonic solution:

water exits the cell; plasmolysis occurs (shrinkage of cytoplasm)

in hypotonic solution:

water enters the cell; cell swells

Molds and fungi have a pH range of

5-6

Essential nutrients

cannot be synthesized and must be supplied otherwise growth ceases

Required MACROnutrients

CHONPS, K+, Mg2+, Ca2+

Cations:

potassium (K+), magnesium (Mg2+), calcium (Ca2+; serve as cofactors or singaling molecules

Required MICROnutrients

Co, CU, Mn, Mo, Ni, Z

Hektoen Enteric Agar

selective for gram negative bacteria and differential for lactose fermentation

bacteria divide by

binary fission

Generation time

lenght of time for a cell to divide (or population to double)

generation time equation

Nt=N0*2^n number of cells after n generations. n= # of generations

Fed batch culture

feed additional nutrients at mid-log phase

Biofilms

Colonies of bacteria that adhere together on surfaces in nature

Biofilm development occurs in stages via

chemical and environmental

key factor in biofilm formation

adherence (fimbriae/pili)

Biofilm formation

1. Attachment
2. Microcolonies
3. Exopolysaccharide production
4. Mature Biolfilm
5. Dissolution and dispersal

Colony

group of ~1 million cells required to start a pure culture

All cells are descended from a

Single cell

inoculum

colony of cells that are added to a culture medium to start a pure culture

Closed system

cells grown in a lab with a fixed volume of liquid enclosed in a container or flask

Nutrients in a closed system are

limited and can not support infinite growth

Microbial Growth curve

lag phase, log phase, stationary phase, death

Lag phase

cells from a pure colony synthesize enzymes required for cell growth

Log phase

cells division occurs at a continuous rate during active growth phase

Stationary phase

nutrient levels are limited; Cells are growing at an equal rate that they are dying

Death phase

Number of viable cells die off

Growth rate is plotted using a

Logarithmic scale

Primary Metabolites

produced during early log and are used by the cell during normal growth

Secondary Metabolites

produced during late log and are required for cell survival

Metabolites are used for

survival purposes during the stationary phase

Cardinal Temperature

the range of temperatures for the growth of a given microbial species

optimal temperature

the best temperature for an organism where it multiplies most rapidly

Microbes are classified into 5 groups based on their

cardinal temperatures (PPMTH)

Psychrophiles

cold-loving microbes (-10 to 15)

Psychrotrophs

cold tolerant microbes (-10 to 35)

Mesophiles

Moderate temperature microbes (10 to 45)

Thermophiles

heat loving microbes (40 to 80)

Hyperthermalphiles

extreme heat loving microbes (75 to 120)

Microbial growth gradient top of test tube to bottom

High O2 to Low O2

Aerobes

Microbes that require O2 and grow where it is abundant

Anaerobes

Microbes that grow where little to no O2 is present

Obligate aerobes

Require O2 and can NOT live without it (Microbial growth at the top of test tube)

Facultative Anaerobes

Grows better in the presence of O2 (Microbial growth all across, more dense near the top)

Microaerophiles

Only require a small amount of O2 (Microbial growth near the middle of tube)

Obligate Anaerobes

Can NOT grow in the presence of O2 (Microbial growth at bottom of tube)

Aerotolerant Anaerobes

Grows in the presence or absence of O2 (Microbial growth evenly distributed all around)

Cells maintain an internal pH near

neutral (7)

Microbes that live in acidic environments have mechanisms that pump protons

out of the cell

Microbes that live in alkaline (basic) environments have mechanisms that pump protons

into the cell

Acidophiles

grow in acidic environments (1 to 5.5)

Neutrophiles

grow in neutral environments (5.5 to 7.9)

Alkaliphiles

grow in alkaline environments (8 to 12)

Water flows from

hypotonic to hypertonic solutions

Solutes such as NaCl can interact with

water molecules which the cell can no longer use

Non-halotolerants

can NOT tolerate moderate salt concentrations

Halotolerants

can tolerate moderate salt concentrations (like your skin)

Halophiles

require high levels of salt (between 1-14%) to survive

Extreme Halophiles

require very high levels of salt (greater than 15%) to survive

Nutritional Factors of Microbial Growth

1. Energy Source
2. Electron Source
3. Carbon Source

Energy Source

consumed energy source for powering metabolic pathways

Phototrophs

obtain energy from sunlight

Chemotrophs

obtain energy from chemical compounds

Electron Source

original molecules supplying electrons to the Electron Transport Chain

Lithotrophs

supply ETC with electrons from reduced inorganic molecules (Ex: H2O, Fe2+)

Organotrophs

supply ETC with electrons from organic molecules (Ex: glucose)

Carbon Source

original carbon-based molecule supplying carbon for creating other cell components

Autotroph

use carbon fixation to capture carbon for making their own food and other cell components

Heterotroph

consume and use organic molecules to supply carbon for creating other cell components

Growth Factors

Small organic molecules that must be provided to bacteria for them to grow

Fastidious Organisms

have complex nutritional requirements (require many growth factors)

Studying microorganisms requires

growing them on a culture medium

Culture Medium

a solid or liquid preparation of nutrient used to grow micoorganisms

Solid Preperation

agar

Liquid Preperation

Broth

Pure Culture

Population of cells that started from a single colony of viable cells

When cultivating microbes, its important to avoid contamination by using

aseptic technique

Aseptic technique

standard practice in lab and medical procedures that prevent contamination

Agar

polysaccharide extracted from marine algae used to solidify liquid media (broth))

Types of Solid Growth Media

Slants, Deeps, and Petri dishes (All require a lid to prevent contamination of other microbes)

Slant

agar in test tube solidified at an angle creating a large surface area for growth

Deeps

agar solidified upright in a test tube

Petri dishes

agar in shallow plastic plates

Streak-Plate Method

most common and simplest way of isolating microbes in a laboratory

inoculator

metal or glass loop used to isolate and transfer colonies between growth media

Types of culture media are classified by their

composition and application in research

Chemically Defined Media

exact composition is known and made of pure chemicals

Chemically Defined media is used when

a researcher wants to control the type and quantity of nutrients added to the media

Chemically Complex Media

Contains a variety of nutrients in the form of cell extracts, exact composition of media does NOT need to be known

Proteins from cell extracts are partially digested into short amino acid chains called

peptones

Peptones

small, soluble protein fragments that can be digested by most bacteria

Selective Media

designed to promote growth of the species of interests and inhibit growth of other species

MacConkey Agar

a selective media used in the medial field to isolate gram-negative intestinal bacteria

MacConkey agar contains crystal violet to inhibit

gram-positive cell growth and bile salts which inhibits non-intestinal bacteria

Differential Media

contain an indicator that allows microbes to be visually distinguished by chemical differences (Ex: Blood Agar plates can identify different types of hemolytic molecules)

Hemolytic

ability of a microbe to cause hemolysis (Lysis of red blood cell)

Hemolytic microbes cause a clear area around the colony forming the

zone of clearance

zone of clearance

important for identifying differents types of microbes

Alpha-hemolysis

colonies are surrounded by a small greenish zone clearing from partial hemolysis

Beta-Hemolysis

colonies are surrounded by a very large zone of clearing from complete hemolysis