Water loss in a high-solute environment causes the protoplasm to shrink away from the intact cell wall.

How do halophiles differ from halotolerant microbes?

Halophiles require high salt concentrations for growth; halotolerant microbes can grow in salty conditions but do not require them.

What does water activity measure?

Water activity ($a_w$) measures available water as the ratio of a material's vapor pressure to that of pure distilled water.

Microorganisms that require high atmospheric pressure for growth.

MicrobiologyLesson 5 of 6 in the course Microbial Growth

Microbial Responses to Salt, Water Availability, Pressure, and Light

4 flashcards · 5 quiz questions · 5 match pairs · 5 fill-in sentences · English

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Summary

Microorganisms must cope with environmental conditions beyond temperature, pH, and oxygen. Salt concentration, available water, atmospheric pressure, and light can all influence whether microbes grow and how they obtain energy.

Most natural environments have a lower solute concentration than the cytoplasm of a microbial cell. In dilute surroundings, a rigid cell wall helps protect many microbes from swelling and bursting. A highly concentrated, salty environment creates the opposite challenge: water moves out of the cell, following its concentration gradient. The cytoplasm shrinks away from the intact cell wall, a process called plasmolysis, which can lead to cell death.

All flashcards

What is plasmolysis?: Water loss in a high-solute environment causes the protoplasm to shrink away from the intact cell wall.
How do halophiles differ from halotolerant microbes?: Halophiles require high salt concentrations for growth; halotolerant microbes can grow in salty conditions but do not require them.
What does water activity measure?: Water activity ( $a_w$ ) measures available water as the ratio of a material's vapor pressure to that of pure distilled water.
What are barophiles?: Microorganisms that require high atmospheric pressure for growth.

Quiz questions

How does a halophile differ from a halotolerant microorganism?Answer: A halophile requires high salt for growth; a halotolerant microorganism does not.
How does *Dunaliella* cope with the high salt concentration of hypersaline environments?Answer: It maintains high cytoplasmic glycerol and actively pumps out salt ions.
Why can drying or adding salt or sugar help preserve food?Answer: These methods reduce available water, making conditions less favorable for microbial growth.
What do Halobacteria use bacteriorhodopsin to do?Answer: Capture light and drive proton and sodium pumps.
Which pairing correctly identifies the light-based nutritional types of these microbes?Answer: Cyanobacteria are photoautotrophs; purple nonsulfur bacteria are photoheterotrophs.

Based on Microbiology by Nina Parker, Mark Schneegurt, Anh-Hue Thi Tu, Philip Lister, Brian M. Forster (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.

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