Chapter 6 2770 Key concepts

Minimum Growth Temperature

The lowest temperature at which an organism can function and grow.

Optimum Growth Temperature

The temperature at which cell metabolism is most efficient, maximizing the growth rate.

Maximum Growth Temperature

The highest temperature at which an organism can still grow.

Extremophiles

Organisms that grow optimally in conditions that mesophiles (normalophiles) would consider hostile.

Extreme-tolerant organisms

Do not grow optimally in extreme conditions but can survive in those conditions for an extended period.

Mesophile

Grows best at moderate temperatures (20°C - 40°C). Human pathogens belong to this group.

Psychrophile (Cryophile)

Grows best at very low temperatures (~20°C or below), found in Arctic and Antarctic regions.

Psychrotroph

Cold-resistant mesophiles that can survive extreme cold but do not thrive in it (20°C - 40°C).

Thermophile

Grows best at high temperatures (above 45°C), found in hot springs and geysers.

Hyperthermophile

Grows best at very high temperatures (above 80°C), found in hot springs and deep-sea hydrothermal vents.

Extreme Halophiles

Require very high salt concentrations (up to 30% NaCl), found in salt flats and salt marshes.

Moderate Halophiles

Tolerate moderate salt concentrations.

Halotolerant

Can tolerate high salt concentrations but do not require them for growth.

Acidophiles

Grow best in acidic conditions (pH 0 - 5), often chemoautotrophs.

Alkaliphiles

Grow best in alkaline conditions (pH 9 - 11), typically found in soda lakes.

Neutralophiles

Grow best in near-neutral pH conditions (pH 5 - 8), includes most human-associated bacteria.

Reactive Oxygen Species (ROS)

Highly reactive molecules that can damage biomolecules such as DNA, proteins, and lipids.

Types of ROS

Include hydroperoxide (O₂H), superoxide (•O₂⁻), hydroxyl radical (OH•), and singlet oxygen (¹O₂).

Oxygen-tolerant cells

Produce antioxidant molecules and DNA repair enzymes to cope with oxidative damage caused by ROS.

Biofilms

Microbial communities that form when organisms locate a surface and decide to stay.

Quorum sensing

The process by which biofilms use communication to determine when the population is large enough to form a biofilm.

Extracellular matrix (ECM)

Secreted by biofilms to hold the cells together, protect them from removal, predators, and chemical assault, and help them adhere to surfaces.

Nutrient sharing in biofilms

Organisms within a biofilm share nutrients, signals, and even DNA to strengthen the community.

Species diversity in biofilms

Biofilms can contain multiple species if the species work well together.

(CFU)

Represents a single viable microbial cell or a group of cells that can form a colony on a solid medium.

Cell Count

Measures the total number of cells, including both living and dead cells.

Selective Media

Allows the growth of specific target microorganisms while inhibiting the growth of others.

Differential Media

Includes a mechanism to distinguish between different types of microorganisms based on their biochemical properties.

Enrichment Media

Promotes the growth of specific microorganisms by providing optimized growth conditions, allowing them to grow faster than other microbes.

Limitations of Culture Techniques

Some microbes cannot be cultured in the lab because their growth requirements are unknown or too complex to replicate.

Lag Phase

The initial phase where cells adapt to their environment and prepare for division, with little to no increase in cell number.

Log Phase (Exponential Phase)

The phase of rapid cell division, where the population grows exponentially and cells are most metabolically active.

Stationary Phase

The phase where the rate of cell division equals the rate of cell death, resulting in a stable population size.

Death Phase

The phase where the number of dying cells exceeds the number of new cells being produced, leading to a decline in the population.

Serial Dilution

A sample of culture is diluted multiple times, typically by factors of 10 each time, and then plated on agar to estimate the original population per mL.

Cell Counting (Microscopic Counting)

A drop of culture media is placed on a special microscope slide with an etched grid pattern to count bacteria one by one under a microscope.

Flow Cytometry

A machine uses a capillary tube to separate cells into a single file line, counting them one by one as they pass through a laser system.

Turbidity (Optical Density)

Provides a quick estimate of population size but does not distinguish between live and dead cells.

Spectrophotometer

Used to measure the scattering of light in a sample, indicating how cloudy (turbid) the sample is.