Microbial Growth and Environmental Influences

Vocabulary flashcards covering microbial growth dynamics, growth curves, enumeration techniques, continuous cultures, physical and chemical environmental parameters, and cell-cell communication from Lecture Six.

Microbial Growth

An increase in cellular constituents that leads either to an accumulation of new cells (increase in cell number via budding or binary fission) or an increase in individual cell size.

Coenocytic Microorganisms

Multi-nucleated organisms without clear cellular distinctions in which nuclear divisions occur without accompanying cell divisions.

Batch Culture Growth Curve

A graphical representation plotting log cell number against time for a population cultured in a closed vessel with a single initial batch of medium, divided into four distinct phases.

Lag Phase

The introductory period of a batch culture with no immediate increase in cell numbers, during which cells replenish depleted components, adapt to new media conditions, and synthesize new cellular machinery.

Log (Exponential) Phase

The growth phase where microorganisms divide at their maximum constant rate, population physical and chemical traits remain uniform, and cells undergo balanced growth.

Balanced Growth

A state in which all cellular constituents are manufactured at constant rates relative to one another, persisting as long as nutrients remain readily available.

Unbalanced Growth

A state where the rates of synthesis of various cell components vary relative to each other, caused by environmental shifts or changes in nutrient levels (shift up or shift down).

Stationary Phase

A phase in which the total count of viable cells remains constant, occurring when metabolically active cells cease reproduction or when the reproduction rate equals the death rate.

Starvation Response

A survival response triggered by nutrient depletion or critical population density, resulting in endospore formation, protoplast shrinkage, nucleoid condensation, chaperone synthesis, and increased virulence.

Death Phase

The phase characterized by an exponential decline in viable cell count due to irreversible loss of reproductive ability, which eventually slows as resistant cells accumulate.

Generation (Doubling) Time

The time period required for a microbial population to double in size, governed by environmental variables and genetic regulation.

Mean Growth Rate Constant

The number of microbial generations produced per unit of time, conventionally expressed as generations per hour.

Petroff-Hausser Counting Chamber

A specialized microscope slide marked with an etched grid and coverslip used for rapid, low-cost direct visual enumeration of eukaryotic and prokaryotic cells.

Coulter Counter

An electrical counting instrument that draws a cell suspension through an orifice to detect electrical current disruptions, capable of counting large cells ($> 1\,\mu\text{m}$) but unable to separate live from dead cells.

Membrane Filter Technique

A cell-counting method in which liquid samples are passed through microporous membranes, followed by fluorescent live-dead staining to differentiate metabolically active cells.

Colony Forming Units (CFU)

The standardized unit of measure used in viable plating procedures to estimate viable cell counts based on colonies that emerge on solid growth media.

Dry Weight

A method of estimating total cell biomass by drying or combusting cells to assess carbon content, which is time-consuming and offers low sensitivity.

Turbidometric Measurement

A rapid, indirect biomass assessment utilizing a spectrophotometer to quantify light scattering, though vulnerable to distortion by sample clumping or environmental debris.

Continuous Culture

An open cultivation setup characterized by continuous addition of fresh medium and removal of spent broth and wastes, locking cells in exponential growth at stable biomass levels.

Chemostat

A continuous culture apparatus maintained by balancing medium inflow and outflow with one limiting nutrient, which operates most effectively at low dilution rates.

Turbidostat

A continuous culture apparatus that modulates media flow to preserve a set turbidity or cell density in the absence of a limiting nutrient, functioning best at high dilution rates.

Dilution Rate

The rate at which nutrient medium passes through a culture chamber relative to the overall vessel volume.

Extremophiles

Organisms specifically adapted to survive and proliferate within extreme physical or chemical conditions that are lethal to most other taxa.

Water Activity ($a_w$)

The quantity of free, unbound water accessible to organisms, reduced by interactions with solute molecules (osmotic effect) or adsorption onto surfaces (matric effect).

Osmotolerant Taxa

Microbes that grow across broad ranges of water activity by accumulating compatible solutes internally to preserve cellular osmotic balance.

Halophiles

Salt-loving microorganisms that require or flourish in high-salinity habitats with elevated concentrations of $\text{NaCl}$.

Acidophiles

Microorganisms whose optimal growth occurs in acidic environments between pH $0$ and pH $5.5$, often employing ion exchange systems to keep their internal cytoplasm near neutrality.

Neutrophiles

Microorganisms that grow optimally between pH $5.5$ and pH $7.0$, representing the habitat profile of most bacteria and protozoa.

Alkalophiles

Microorganisms that thrive optimally at elevated alkaline conditions between pH $8.5$ and pH $11.5$, commonly dominated by cyanobacteria.

Cardinal Growth Temperatures

The species-specific minimum, optimum, and maximum temperature thresholds that define an organism's capacity to grow.

Psychrophiles

Microorganisms adapted to cold environments with growth temperature ranges between approximately $0^\circ\text{C}$ and $20^\circ\text{C}$.

Mesophiles

Microorganisms adapted to moderate temperatures, possessing growth boundaries between $20^\circ\text{C}$ and $45^\circ\text{C}$.

Thermophiles

Microorganisms that thrive at high temperatures, exhibiting growth ranges between $45^\circ\text{C}$ and $65^\circ\text{C}$.

Extreme Thermophiles

Organisms that have evolved to grow at extreme temperatures exceeding $65^\circ\text{C}$.

Microbial Oxygen Requirements (Growth Patterns in Culture Tubes)

Differential growth distributions according to oxygen exposure: obligate aerobes gather at the oxygen-rich surface, facultative anaerobes concentrate near the top but distribute throughout, aerotolerant anaerobes disperse evenly, strict anaerobes isolate at the bottom, and microaerophiles settle at low concentrations ($< 2\text{--}10\%\,\text{O}_2$) beneath the surface.

Superoxide Dismutase (SOD) and Catalase

Protective enzymatic defenses synthesized by aerobic organisms to neutralize toxic metabolic reduction products of oxygen, such as superoxide radicals and hydrogen peroxide ($\text{H}_2\text{O}_2$).

Barotolerant Taxa

Organisms whose growth is inhibited by increased hydrostatic pressure, though they tolerate high pressures better than nontolerant species.

Barophilic Taxa

Microorganisms that grow more rapidly or strictly require high hydrostatic pressure conditions to proliferate.

Electromagnetic Spectrum

The spectrum of radiation spanning from high-energy ionizing wavelengths ($\text{X-rays}$ and gamma rays) through ultraviolet and visible light ($400\text{--}700\,\text{nm}$) to infrared and radio waves.

Thymine Dimerization

DNA damage caused by ultraviolet (UV) radiation in which adjacent thymines covalently link to one another on the same strand, arresting DNA polymerase and driving lethal mutations.

Photoreactivation

A microbial enzymatic repair mechanism in which UV-induced thymine dimers are directly cleaved and separated in the presence of visible light.

Dark Reactivation

A bacterial DNA repair process where thymine dimers are enzymatically excised and replaced with correct nucleotides without requiring light.

Carotenoid Pigments

Accessory pigments synthesized by many photosynthetic organisms that function as antioxidants to quench singlet oxygen ($^1\text{O}_2$) and shield the cell from photo-oxidation.

Liebig's Law of the Minimum

An ecological principle stating that the total biomass of a population is controlled by whichever essential nutrient is present in the lowest concentration relative to requirements.

Shelford's Law of Tolerance

An ecological principle establishing that beyond specific upper and lower environmental limits, an organism cannot survive or grow regardless of the abundance of nutrients.

Quorum Sensing

A mechanism of population density-dependent microbial communication and cooperation driven by the release and detection of extracellular chemical signaling molecules.