Microbiology Ch. 7 - Microbial Growth and Nutrition

Exam 1

microbial reproduction

called binary fission

cell mass doubles, DNA replicates and two strands separate, synthesis of a partition or septum separates the cell into two genetically identical cells

generation (or doubling time)

the interval of time between successive binary fissions

what does shorter doubling time mean?

shorter incubation period of disease

microbial growth phases

lag: no cell division occurs, bacteria adapt to their environment

log: exponential growth, human disease symptoms develop

stationary: reproductive and death rates equalize

decline: accumulation of waste products and scarcity of resources

endospores

responsible for nutrient limitation

highly resistant structure formed by species of bacillus and clostridium when nutrient supplies are low

resistant to desiccation and heat

core contains small acid-soluble proteins (SASPs)

ca2+ linked dipicolinic acid is absent in vegetative cells

formation of bacterial spore

1. DNA replicates

2. one chromosome condenses at the end of the cell and it pushes its way into the cell as a transverse septum

3. transverse septum forms, and the primitive spore, the forespore (contains cytoplasm, DNA, and dipicolinic acid, which stabilizes proteins and DNA), is cut from the remainder of the cell

4. the outer layer, the cortex, developed around the forespore, and pieces of the spore coat form

5. the walls of the spore are complete, and the mature spore is formed while the vegetative cell disintegrates

6. the free spore is released, and under favorable nutrient conditions, the spore will germinate and develop into a vegetative cell

germination

form spore to vegetative cell when environmental conditions are favorable again, breaking down protective layers

optimal prokaryotic growth factors

temperature, oxygen, pH, and osmotic conditions

psychrophiles optimal temperature

15 °C

largest portion of all prokaryotes on earth

mesophiles optimal temperature

10-45 °C

pathogens that thrive in the human body

thermophiles optimal temperature

60 °C

live in compost heaps and hot springs

hyperthermophiles

80+ °C

archaea that are found in sea floor hot water vents

obligate aerobes

require oxygen to grow

anaerobes

do not or cannot use oxygen

aerotolerant species are insensitive to oxygen

obligate anaerobes

killed by oxygen

facilitive prokaryotes

grow with oxygen or in reduced oxygen environments

capnophilic bacteria

require low oxygen and lots of carbon dioxide

thioglycollate broth

used to test an organism’s oxygen sensitivity

majority of species grow optimally in what pH?

neutral, 7.0 pH

acidophiles

acid-tolerant prokaryotes

barophiles

can withstand high hydrostatic pressure

halophiles

salt-tolerant prokaryotes

complex medium

(think unknown composition) chemical unidentified medium

synthetic medium

(think made, known) chemical composition is known

selective medium

(think two different cannot be together) contains ingredients to inhibit the growth of certain species and allow the growth of others

differential medium

(think two different can be together) contains specific chemicals to indicate species that possess or lack a biochemical process

act as visual indicators to show differences (dyes, cells, etc.)

enriched medium

required by some fastidious organisms

adds extra nutrients

streak-plate isolation method

spreads out individual cells to form discrete colonies of species