G: Environmental Factors Influencing Growth

Question 1

What does -phile mean

Answer 1

means prefer and often means requires

Question 2

What does -tolerant mean

Answer 2

will grow in a wider range of conditions than non-tolerant

Question 3

What does -facultative mean

Answer 3

optional mode

Question 4

What does -obligate mean

Answer 4

an absolute requirement

Question 5

What does -hyper mean

Answer 5

above/greater than

Question 6

What does -extreme mean

Answer 6

outside of normal range

Question 7

How is water activity expressed as, and what does it reflect

Answer 7

a_w, reflects how wet/dry an environment is and concentration of solutes dissolve in the water

Question 8

Equation for a_w

Answer 8

a_w= Ps_oln/P_water where =vapour pressure

Question 9

Give the range of a_w. What does this mean

Answer 9

0 to 1. The higher the [soulte] the lower the water activity. Water has an a_w of 1

Question 10

How does bacterial cells in an environment with high a_w protect themselves

Answer 10

by their peptidoglycan

Question 11

When will bacterial cells undergo plasmolysis

Answer 11

in an environment with low a_w (<0.9)

Question 12

What is the typical a_w minimum for bacteria

Answer 12

0.95-0.98

Question 13

What are osmotolerant bacteria called if solute is NaCl

Answer 13

halotolerant

Question 14

give an example of halotolerant bacteria and a_w limit

Answer 14

Staphyloccocus spp. lower limit is 0.85

Question 15

What are halophiles

Answer 15

adapted to grow in presence of salts like NaCl, require high levels to grow

Question 16

How do osmotolerant and halophilic bacteria prevent plasmolysis

Answer 16

must keep internal [solute] the same or higher than that of enivironment

Question 17

How is internal [solute] the same as the enivironment. Hint: uptake

Answer 17

by uptake of synthesis of a compatible solute

Question 18

What are compatible solutes

Answer 18

hydrophilic molecules/ions that do not affect cellular fn. eg aa, sugars or ionic compounds like KCl

Question 19

Would H⁺ work as a compatible solute

Answer 19

no too acidic, must select stg that is neutral to environment

Question 20

application of water availability

Answer 20

food preservation: dried or freeze dried (water is frozen and then sublime in a vacuum) and sugar/salt added

Question 21

How can bacteria be preserved

Answer 21

lyophilized (freeze dried)

Question 22

what is the optimal pH

Answer 22

it varies, bacterial growth is affected by environmental pH

Question 23

acidophiles optimum pH is

Answer 23

under 5.5

Question 24

most bacteria have a pH of? they are called

Answer 24

optimal pH of 7 called neutrophiles

Question 25

give an example of neutrophile

Answer 25

gram -ive _Helicobacter pylori_

Question 26

how does _Helicobacter pylori_ protect itself from stomach acid

Answer 26

secretes urease. substrate for urease is urea. one product of this rxn is ammonia which can bind hydrogen ions and therefore increase the pH

Question 27

alkalophiles optimum pH is

Answer 27

over 8.0

Question 28

application of alkalophiles

Answer 28

some _Bacillus_ spp. can secrete proteases and lipases that are stable at high pH. theses enzymes are produced industrially and added to laundry detergents

Question 29

what does the optimal pH refer to

Answer 29

extreme environment only. cytoplasmic pH must remain near neutral (in most bacteria) to prevent denaturation of proteins and nucleic acids

Question 30

Why are buffers added to batch culture media

Answer 30

some bacteria produce waste products that change pH of environment. buffers keep media at optimal pH for the species being grown

Question 31

name an acid tolerance bacteria

Answer 31

_E. coli_ O157:H7 has adapted to lower pH, helps it survive acidic human stomach