Microbio Exam 1 Week 5

pH

acidity or alkalinity of a solution

Barophiles

microorganisms that require high pressure for growth

produce enzymes that can function at high pressures and are useful in high pressure bioreactors, toxic clean up in deep sea, and high pressure food processors

Water Availability

depends on how moist/dry an environment is and the concentration of solutes dissolved in water

measured as water activity (Aw), values vary between 0 (no free water) and 1 (pure water)

Halophiles

require high salt concentration in their medium

can grow and multiply in the presence of high salt but don’t require it for growth

Nitrogen Cycle

converts nitrogen to various forms like proteins and nucleic acids

Nitrogen Fixation

converts N2 to ammonium ions (NH4+), which can be used for biosynthesis

Nitrification

organisms transform ammonia to nitrate

Denitrification

convert nitrate to N2

Binary Fission

way of bacteria reproduction

origin of replication

replication continues in the opposite directions along chromosome until terminus is reached

Growth

formation of septum during division

proteins: FtsZ and tubulin

Generation (Doubling) Time

time it takes for the population to double through one round of binary fission

varies depending on species or microorganism and environment

Growth Curve Stages

lag phase: intense activity preparing for population growth, population growth hasn’t started yet

log phase: either a logarithmic or exponential increase in population

stationary phase: period of equilibrium, deaths balance growths

death/decline phase: population decreases at a logarithmic rate

Endospores

mature ones are very dehydrated and contain calcium dipicolinate and small acid soluble spore proteins (SASPs)

SASPs bind tightly to DNA in the core and protect it from damage from UV radiation, desiccation, and dry heat

Chemostat

used to maintain a continuous culture where nutrients are supplied at a steady rate

culture media is constantly added (feed) and constantly removed (effluent)

microorganisms are always in exponential growth

ex: human GI tract

Chemostat Biofilms

complex and dynamic ecosystems commonly formed on surfaces

growth occurs in stages

1. flagella attaches

2. micro colonies form

3. cells produce EPs

4. biofilm matures

5. biofilm dissolves and cells disperse

Agar

complex polysaccharide

used as solidifying agent for culture media in petri plates, slants, and deeps

generally not metabolized by microbes

liquefies at 100* and solidifies at 40*

Culture Media

provides essential nutrients for bacteria

Chemically Defined Media

the exact chemical composition is known

Complex Media

made of nutrients including extracts from yeasts, meat, plants, or digests of proteins from other sources

exact chemical makeup varies slightly from batch to batch

Minimal Medium

components are limited to only those nutrients the organisms needs in order to grow

Enrichment Culture

usually liquid and provides nutrients and environmental conditions that favor the growth of a particular microbes, but not others

designed to increase very small numbers of the desired type of organism in detectable levels

Selective Media

suppress the growth of unwanted bacteria and encourage the growth of desired microbes

Differential Media

makes it easier to distinguish colonies of the desired organism from other colonies growing on the same plate

Pure Cultures

one bacterium gives rise to one colony

isolation streaking allows for seperation of colonies into cultures

a population of identical cells

Culturing Anaerobes

anaerobe jar (for plates) where O2 is removed and CO2 is generated

anaerobic chamber filled with inert gases (N2, H2, and CO2) is equipped with air locks to introduce cultures and materials

Problems with Oxygen

molecular oxygen (O2) isn’t toxic but can be converted to toxic oxygen by-products and these can be harmful or kill cells not able to deal with them

toxic forms of oxygen and the enzymes that protect the cell from their activity

Direct Microscopic Count

uses a counting chamber

doesn’t necessarily yield an accurate count of live cells

not always possible to distinguish between live cells, dead cells, and debris of the same size under the microscope

Enumeration of Bacterial Cells

can be done with an electronic instrument called fluorescence-activated cell sorter (FACS), that can count cells with different properties

can count and separate bacterial cells that synthesize a fluorescent protein from cells that don’t

Proof of Life (Viable Counts)

can replicate and form colonies on an agar plate

Obtaining Pure Cultures

can be isolated using a spread plate technique

early dilutions will show confluent growth and each colony on the agar plate represents one viable organism

Serial Dilutions

enumerate (count) bacterial cells

the viable plate count, is a count of viable or live cells

the results can usually be expressed as colony forming units per millimeter

Turbidity

using plate counts or direct counting to monitor cell number often takes too long to carry out when cells in a specific growth phase are desired

measures cell number of growing microbes in a culture

can be measured in real time using a spectrophotometer, which passes a beam of light through a culture sample

Optical Density

decrease in intensity of light due to the scattering of light

Ways to Preserve Bacterial Cultures

deep freezing

lyophilization (freeze drying): frozen and dehydrated in a vacuum

Sergei Winogradasky

developed an early form of enrichment culture to study interactions between soil microorganisms