LAB 8 - Effect of Ionic Composition on Microbial Growth

Question 1

Non halophiles

Answer 1

• Live in environments with extremely low levels of salinity
• Able to grow in media lacking salt, commonly inhibited by low salt concentrations

Question 2

Halotolerant

Answer 2

Tolerate low to moderate levels of salt but are able to grow in its absence

Question 3

Halophilic

Answer 3

• Live in environments with high salt concentrations (e.g. seawater)
• Require salt for growth
• Can be inhibited by very high salt concentrations
• E.g. Vibrio species require ionic composition similar to that of seawater

Question 4

Salt level of seawater

Answer 4

3.5% NaCl w/v

Question 5

Extreme halophiles

Answer 5

• Require very high salinity conditions for growth
• Able to grow in salt saturated conditions (e.g. salt lakes)
• Optimum NaCl concentration for growth ranges from 15-30%

Question 6

How many test organisms were used in experiment

Answer 6

4

Question 7

Halobacterium salinarum

Answer 7

• Member of the Archaea
• Grown in liquid media as it does not grow well on agar

Question 8

Which species were used as test bacterium in experiment

Answer 8

• E. coli
• Staphylococcus aureus
• Vibrio harveyi
• Halobacterium salinarum

Question 9

Salt concentrations of media

Answer 9

0, 2, 8, and 25%

Question 10

Which test organism was positive for bioluminescence

Answer 10

V. harveyi

Question 11

In physiological terms, what could explain the inhibition of some of the microbes under high salt conditions and the tolerance of others to salt concentrations as high as 25%, and vice versa?

Answer 11

• High salt concentrations create an osmotic environment that can lead to cell dehydration.
• Halophilic organisms have specialized mechanisms (e.g., compatible solutes) to retain water and thrive.
• Non-halophiles like E. coli and S. aureus lack these adaptations, leading to cell lysis or growth inhibition.

Question 12

The cultures of H. salinarum have a pink-ish colour to them. What is the source (or sournces) of the pink colour? What family of compounds do the compounds belong to and what is their role?

Answer 12

• Pink color comes from carotenoid pigments
• These compounds are part of the retinal-based photopigments.
• Involved in light-driven ATP synthesis and phototrophy and provides protection against UV radiation

Question 13

Describe the process underlying the regulation of bioluminescence in Vibrio harveyi.

Answer 13

• Bioluminescence regulated by quorum sensing mechanisms.
• At high cell densities, autoinducers (e.g., AHLs) accumulate.
• Binding of autoinducers to receptors triggers expression of luciferase genes.
• Light production is advantageous for communication and attracting prey in marine environments