• referring to the increase in size of a population of microbes
• not individual microbe size- but individual reproduction contributes to growth

• a carbon source
• a source of energy
• a source of electrons or hydrogen atoms

• organisms that utilize an inorganic source of carbon (ie: CO2) as their sole source of carbon
• these acquire electrons or hydrogen atoms from inorganic molecules=lithotrophs

• catabolize reduced organic molecules (ie: proteins, carbs, amino acids, and/or fatty acids) they acquire from other organisms
• these acquire electrons from the same organic molecules that provide them carbon=organotrophs

• photoautotrophs- light and CO2
• chemoautotrophs- redox rxns and CO2
• photoheterotrophs- light and organic molecules
• chemoheterotrophs- redox reactions and organic molecules

• a chemical that is needed in order to continue metabolism
• lack of this nutrient interrupts metabolism

• oxygen is essential for these organisms because it serves as the final electron acceptor of electron transport chains
• algae, most fungi and protozoa, and many prokaryotes

• singlet oxygen: neutralized by pigments called carotenoids
• superoxide radical: detoxified by superoxide dismutase
• peroxide anion: detoxified by catalase or peroxidase
• hydroxyl radical: most reactive of the toxic forms of O2

• molecular oxygen with electrons that have been boosted to a higher energy state, typically during aerobic metabolism
• very reactive oxidizing agent.
• human WBC's use it to oxidize pathogens
• phototrophs contain pigments called "carotenoids" that prevent toxicity by removing the excess energy of singlet oxygen

• formed during the incomplete reduction of O2 during electron transport in aerobes and during metabolism by anaerobes in the presence of O2
• so reactive and toxic that aerobes must produce enzymes called "superoxide dismutases"
• anaerobes lack superoxide dismutase, therefore susceptible to this particular O2 toxicity

• another highly reactive oxidant contained within hydrogen peroxide that is formed during reactions catalyzed by superoxide dismutase
• peroxide anion is what makes hydrogen peroxide an antimicrobial
• aerobes contain either catalase or peroxidase in order to detoxify

• most toxic form of oxygen
• result from ionizing radiation and from the incomplete reduction of hydrogen peroxide
• this does not accumulate in aerobic cells (because of catalase and peroxidase)

• aerobes which can maintain life via fermentation or anaerobic respiration, though their metabolic efficiency is often reduced in the absence of oxygen
• a few yeasts and numerous prokaryotes

• microorganisms which prefer anerobic conditions but can tolerate low levels of oxygen
• they do not use aerobic metabolism
• tolerate oxygen by having some of the enzymes that detoxify oxygen's poisonious forms

• organisms which require low levels of oxygen
• ie: H. pylori requires oxygen levels of 2 -10%

nitrogen 

(for growth requirements)

• essential element for growth
• contained in many organic compounds including the amine group in amino acids and part of nucleotide bases
• often a growth-limiting nutrient for many organisms
• acquired from organic and inorganic compounds
• most photosynthetic organisms can reduce nitrate to ammonia (which can then be used for biosynthesis)
• some bacteria capable of nitrogen fixation

• process of reducing nitrogen gas (N2) to ammonia (NH3)
• few bacteria are capable of this process, notably many cyanobacteria, as well as Rhizobium
• essential for life on earth because nitrogen-fixers provide nitrogen in a usable form to other organisms

phosphorus

(for growth requirements)

sulfur

(for growth requirements)

• component of sulfur-containing amino acids
• these bind to one another via disulfide bonds that are critical to the tertiary structure of proteins

• microorganisms that can synthesize all of their metabolic and structural needs from inorganic nutrients
• they have every enzyme and cofactor needed to produce all of their cellular components
• includes: algae and photosynthetic bacteria

• note: most organisms can not synthesize all of their needed organic chemicals
• definition: organic chemical such as a vitamin required in very small amounts for metabolism
• recall: vitamins constitute all or part of many coenzymes
• other examples: some amino acids, purines, pyrimidines, cholesterol, NADH, and heme

temperature

(for growth requirements)

• effects the 3-D configurations of biological molecules
• can denature proteins
• can alter temperature-sensitive hydrogen bonds of proteins
• can also effect lipids within membranes

• organisms that grow best between temperatures ranging from 20*C - 40*C
• note: body temperature is 37*C, so most human pathogens are mesophiles

• these grow best in a narrow range around neutral pH, usually between 6.5-7.5
• includes: most bacteria and protozoa, inluding pathogens
• note: this is the pH range for most of the tissues and organs within the human body

• organisms which grow best in an acidic habitats
• obligate acidophiles: require an acidic environment and die if the pH approaches 7
• acid-tolerant microbes: merely survive in acid without preferring it
• ie: H. pylori

• the pressure exerted on a semipermeable membrane by a solution containing solutes
• higher concentration of solutes = hypertonic
• lower concentration of solutes = hypotonic

• microorganism requiring high osmotic pressure
• ie: Great salt lake or smaller salt ponds

• water exerts pressure in proportion to its depth
• for every additional 10 m of depth, water pressure increases 1 atmosphere (atm)

• organisms that live under extreme hydrostatic pressure
• their membranes and enzymes depend on pressure to maintain their three dimensional shapes

• complex relationships among numerous microorganisms, often different species, attached to surfaces
• they develop an extracellular matrix, composed of DNA, proteins, and primarily the tangled fibers of polysaccharides the cell's glycocalyces

• sample of microorganisms
• usually placed in media in order to culture

• can refer to either the act of cultivating organisms (verb)
• or the microorganisms cultivated (noun)

• sample of human material, such as feces or blood, that is examined or tested for the presence of microbes
• often transported in special transport media

• cultures composed of cells arising from a single progenitor
• aka "axenic"
• the progenitor=CFU's

• colony forming units
• a single cell or related cells that produce a colony

• aka synthetic medium
• one in which the exact chemical composition is known

• these require a relatively large number of growth factors
• these can be used to test for presence of the specific growth factors needed by the organism (living assays)

• culturing media that contains nutrients released by the partial digestion of yeast, soy, beef, or other proteins; thus the exact chemical composition is unknown
• most chemoheterotrophs, including pathogens, are grown in this type of media

• both selective and differential medium
• inhibits the growth of Gram-positive bacteria
• differentiates lactose-fermenting from non-lactose-fermenting Gram-negative bacteria

• special media that provides better anaerobic culturing conditions
• contains compounds such as sodium thioglycollate that chemically combine with free oxygen and remove it from the medium

• machines that electronically monitor and control CO₂ levels
• these provide atmospheres that mimic the environments of the intestinal tract, the respiratory tract, and other body tissues 

• smaller and less expensive alternative to CO₂ incubator
• culture plates are sealed in a jar with a lit candle, the flame consumes most of the O₂ replacing it with CO₂ and the candle extinguishes itself
• creates an environment suitable for aerotolerant anaerobes, microaerophiles, and capnophiles

• technique used to enhance the growth of less abundant microorganisms by using a selective medium
• designed to increase very small numbers of a chosen microbe to observable levels
  
• method introduced by Beijernick in the late 1800's

• incubation of a specimen in a refrigerator to enhance the growth of cold-tolerant species
• ie: Vibrio cholerae

refrigeration

(for storage)

• long-term storage of bacterial cultures at temperatures ranging from -50*C to -95*C
• stores for several years

• removal of water from a frozen culture or other substance by means of vacuum pressure
• used for long-term storage preservation of food and cells
• typically can be stored for decades

• reproduction process of most unicellular microorganisms
• process in which a cell grows to twice its normal size and divides in half to produce two daughter cells of equal size

1. cell replicates its chromosomes and attaches to the cell membrane
   
2. cell elongates and growth between attachment sites pushes the chromosomes apart
   
3. the cell forms a new cytoplasmic membrane and wall (septum) across the midline
   
4. when the septum is complete, the daughter cells may remain attached or may separate completely

• aka exponential growth
• increase of size of a microbial population in which the number of cells doubles in a fixed interval of time
• to calculate the number of cells in a population, we multiply the original number of cells by 2ⁿ

• the time required for a bacterial cell to grow and divide
• the time required for a population of cells to double in number

• cells are adjusting to their new environment
• most cells do not reproduce immediately, but instead actively synthesize enzymes to utilize novel nutrients in the medium

• population increases logarithmically
• reproduction rate reaches a constant as DNA and protein syntheses are maximized

• the number of dying cells equals the number of cells being produced
• the size of the population remains constant

• cells die at a faster rate than those being produced
• occurs as nutrients become more limited and waste products increase

• an open system in which fresh medium is continuously supplied while an equal amount of old medium (containing microbes) is removed
• done to maintain a particular phase of microbial growth

a stepwise dilution of a liquid culture in which the dilution factor at each step is constant

• estimation of the size of a microbial population based on the number of colonies formed when diluted samples are plated onto agar media
  
• count the colonies on a plate with 25-250 colonies and multiply by the reciprocal of the dilution ratio to estimate the number of bacteria per ml of the original culture

• technique used if the population density is very small
  
• large sample is poured through a filter small enough to trap cells
  
• the number of colonies trapped on the filter is equal to the number of CFU's in the original large sample

• statistical estimation of the size of a microbial population based upon the dilution of a sample required to eliminate microbial growth
  
• based on the fact that the more bacteria there are in a sample, the more dilutions are required to reduce their number to zero
• number of tubes showing growth in each dilution set is used to enter into an MPN table
  

• sample is placed onto a cell counter, which is a glass slide composed of an etched grid positioned beneath a glass cover slip
• calculated by multiplying the number of bacteria per square by 1,250,000

• a device that directly counts cells as they interrupt an electrical current flowing across a narrow tube held in front of an electronic detector
  
• flow cytometry is a variation of the Coulter counter which uses a light-sensitive detector to record changes in light transmission through the tube as cells pass

• indirect counting method
  
• under standard temperature conditions, the rate at which a population of cells utilizes and produces wastes depends on their number
  
• once the metabolic rate is established, scientists can indirectly estimate the number of cells in a culture

• abundance of filamentous microorganisms are difficult to measure by direct methods
• instead these are filtered from their culture medium, dried and weighed
• suitable for broth cultures

• as bacteria reproduce in a broth culture, the broth often becomes turbid (cloudy) 
  
• the more bacteria within a broth, the more light will be absorbed and scattered, and less light will pass through and strike a light-sensitive detector
• only accurate if cells are suspended uniformly (no sediment)