Chapter 9 - Microbial Growth

Microbiology

microbial growth occurs at the increase of what 2 levels

size and population

division of bacterial cells - parent cells creating 2 daughter cells

binary fission

cells begin synthesizing necessary molecules and increases activity relevant to division (Step 1)

increased metabolism

cell replicates its chromosome and begins to enlarge (step 2)

growth and replication

chromosomes affix to the cytoskeleton and are separated as the two cells continuing growing in separate directions. Septum between the two begin to form (Step 3)

chromosome division and separation

Septum fully separates the two cells at the center, creating two cell chambers (Step 4)

full separation

cell wall of the two cells is fully separated (Step 5)

Cleavage

doubling time - time required for a complete fission cycle

generation time

each new fission cycle increases the population by a factor of two

exponential growth

predictable pattern of growth over time in laboratory studies

growth curve

flat period of adjustment, enlargement, little growth

lag phase

period of maximum growth when cells have adequate nutrients and a favorable environment

exponential growth phase

rate of cell growth equals rate of cell death - caused by depleted nutrients/O2, excretion of organic acids and pollutants

stationary phase

as limiting factors intensify, cells die exponentially

death phase

degree of cloudiness of the nutrient culture media reflects the relative population size of (most simple)

turbidimetry

counting the numbers of cells in a sample microscopically

direct cell count

free floating or swimming microbes

planktonic

planktonic cells attach to substrate by some form of extracellular matrix that binds them together in complex organized layers

biofilms

combination of polysaccharides, proteins, and DNA to help cells adhere to each other and surfaces

Extracellular polymeric substance (EPS)

contains many bacteria, bacteria become specialized in their roles, thick environment for protection, can pump out bacteria to other locations

biofilm features

microbial communication on a molecular level. Used to detect density of population (density dependent)

quorum sensing

human body is a rich habitat for symbiotic bacteria, fungi, and a few protozoa - normal microbial flora

human microbiome

totality of adaptions organisms make to their habitat

niche

temperature, oxygen requirements, pH, osmotic pressure, barometric pressure, light

factors that affect the function of metabolic enzymes

lowest temperature that permits a microbes growth and metabolism

minimum temperature

highest temperature that permits a microbes growth and metabolism

maximum temperature

promotes the fastest rate of growth and metabolism

optimum temperature

optimum temperature below 15C, growth at 0C

psychrophiles

optimum temperature 20-40C, most human pathogens

mesophiles

optimum temperature greater than 45C

Thermophiles

cannot grow without oxygen

Obligate aerobe

utilizes oxygen but can also grow in its absence

Facultative anaerobe

requires only a small amount of oxygen

microaerophile

lacks enzymes to detoxify oxygen so cannot survive in an oxygen environment

obligate anaerobe

do not utilize oxygen but can survive and grow in its presence

Aerotolerant anaerobes

grows best at higher CO2 tensions than normally present in the atmosphere

Capnohile

measure of hydrogen ions

pH

majority of microorganisms grow at a pH between 6-8

neutrophiles

grow at extreme acidic/low pH

Acidophiles

grow at extremely high/alkaline pH

Alkaliphiles

water concentration is equal inside and outside the cell. Rates of diffusion are equal in both directions

isotonic solution

net diffusion of water is into the cell, swells protoplast and pushes it tightly against the wall. Wall prevents cell from bursting if there is a cell wall

hypotonic solution

water diffuses out of the cell and shrinks the cell membrane away from the cell wall, plasmolysis, may cause it to stink and become distorted if there is no wall

hypertonic solution

most microbes exist under hypertonic or isotonic conditions

osmotic pressure

organisms adapted to high osmotic pressures

osmophiles

organisms that adapted to and prefer high salt concentrations

halophiles

ability to grow with or without high osmotic pressure

osmotolerant

can survive under extreme pressure and will rupture if exposed to normal atmospheric pressure

barophiles