Micro Chapter 6: Microbial Growth

two daughter cells

the increase in the number of cells, which occurs by cell division

a cell duplicates its components and divides into two cells

cell division in yeast and a few bacteria where a small, new cell develops from the surface of an existing cell and subsequently separates from the parent cell

mixture of substances on or in which microorganisms grow

b. Increase in size and produce large quantities of ATP

• a. Population growth occurs at an exponential, or logarithmic (log) rate
• b. Organisms divide at their most rapid rate

regular, genetically determined interval

stair-step pattern

1/20 of cells dividing every minute

the rate at which energy can be produced in the form of ATP

When cell division decreases to the point that new cells are produced at the same rate as old cells die

• a. As conditions in the medium become less and less supportive of cell division, many cells lose their ability to divide, and thus the cells die
• b. Decreases at a logarithmic rate

cells assume a variety of unusual shapes, which makes them difficult to identify

all the descendants of an original cell

a Petri dish containing a nutrient medium solidified with agar (a complex polysaccharide extracted from certain marine algae)

is 30 – 300 per plate

Uses a specially calibrated, etched glass slide called a Petroff-Hausser counting chamber (hemocytometer)

2. Dilute to where some test tubes contain 1 organisms and some none (testing water purity)

A known volume of water or air is drawn through a filter with holes too small to allow passage of bacteria

indicates presence of organisms

• a. Spectrophotometer
• b. Subject to error when cultures contain fewer than 1 million cells per milliliter

Include pH, temperature, oxygen concentration, moisture, hydrostatic pressure, osmotic pressure, and radiation

the pH at which microbes grow best

grow best at a pH of 0.1 to 5.4 (Lactobacillus)

exist from pH 5.4 to 8.0

exist from pH 7.0 to 11.5 (Vibrio cholera grows best at pH 9.0)

the organism must have the specified environmental condition

the organism is able to adjust to and tolerate the environmental condition, but it can also live in other conditions

(cold-loving organisms) grow best at temperatures of 15* to 20*C, although some live quite well at 0*C

(Bacillus globisporus) cannot grow above 20*C

(Xanthomonas pharmicola) grows best below 20*C but can grow above that temperature

grow best at temperatures between 25* and 40*C.

Human pathogens

ordinarily live as mesophiles but can withstand short periods of exposure to high temperatures

(heat-loving organisms) grow best from 50* to 60*C

can grow only at temperatures above 37*C

can grow both above and below 37*C

the lowest temperature at which cells can divide

the highest temperature at which cells can divide

the temperature at which cells divide most rapidly

(Pseudomonas) must have free oxygen for aerobic respiration

(Clostridium botulinum, C. tetani, and Bacteroides) are killed by free oxygen

a. Killed by superoxide

appear to grow best in the presence of a small amount of free oxygen

carbon dioxide-loving organisms

ordinarily carry on aerobic metabolism when oxygen is present, but they shift to anaerobic metabolism when oxygen is absent (Staphylococcus and E. Coli)

Have the most complex enzyme systems

can survive in the presence of oxygen but do not use it in their metabolism

Pressure exerted by standing water, in proportion to its depth

bacteria that lice at high pressures, but die in atmospheric pressure

shrinking of the cell

salt-loving organisms

microbes that have special nutritional needs that can be difficult to meet in the laboratory

glucose and other organic molecules

amino groups

synthesize ATP, phospholipids, and nucleic acids

an organic substance that an organism requires in small amounts and that is typically used as a coenzyme

The number of nutrients it must obtain to grow

usually produces by Gram-positive rods, which act in the medium around the organism

usually produced by Gram-negative organisms, which act in the periplasmic space

they metabolize nutrients

they synthesize molecules required for growth

Bacillus, Clostridium, and a few other Gram-positive genera.

stationary phase

Protective or survival mechanism, not a means of reproduction

living part of the endospore

consisting of a cell membrane but lacking a cell wall, grows around the core, enclosing it in a double thickness of cell membrane (synthesizes peptidoglycan)

protects the core against changes in osmotic pressure (drying)

is laid down around the cortex by the mother cell

a lipid-protein membrane

a spore returns to its vegetative state

usually requires some traumatic agent such as low pH or heat, which damages the coat

requires water and a germination agent that penetrates the damaged coat

occurs in a medium with adequate nutrients. Proteins and RNA are synthesized, and in about an hour, DNA synthesis begins

spherical, thick-walled cells, that resemble endospores

Metabolically inactive and resist drying

chains of aerial spores with thick outer walls

a culture that contains only a single species of organism

• a. A series of dilutions are made such that the final dilution contains about 1,000 organisms
• b. It is particularly useful for growing microaerophiles that cannot tolerate exposure to oxygen in the air at the surface of the medium

a medium prepared in the laboratory from materials of precise or reasonable well-defined composition

one that contains known specific kinds and amounts of chemical substances

contains reasonable familiar materials but varies slightly in chemical composition from batch to batch

a product of enzyme digestion of proteins, common ingredient of complex medium

made from mil protein, contains many amino acids and is used to enrich certain media

one that encourages the growth of some organisms but suppresses the growth of others (SPS agar)

has a constituent that causes an observable change ( a color change or a change in pH) in the medium when a particular biochemical reaction occurs

contains special nutrients that allow growth of a particular organism that might not otherwise be present in sufficient numbers to allow it to be isolated and identified

one an organism has been isolated, it can be maintained indefinitely in a pure culture

minimize the chances that cultures will be contaminated by organisms from the environment or that organism, especially pathogens, will escape into the environment

A culture in which organisms are maintained in a dormant state

freeze-drying

a preserved culture that maintains the organisms with the characteristics as originally defined