MT

chapter 4 microbiology

Chapter 4: Microbial Growth

Exodus Reference

  • Exodus 10:5: Cultural impact of swarms covering the land. Emphasizes the influence and dominance of microorganisms.

A Glimpse of History

  • Robert Koch (1843–1910):

    • German physician known for studying disease-causing bacteria.

    • Awarded Nobel Prize in 1905.

    • Developed methods to cultivate bacteria on solid media.

    • Early Experiments:

      • Utilized potatoes but faced nutrient limitations.

      • Introduced gelatin to solidify media, faced melting temperature issues.

    • Agar (suggested by Fannie Hess in 1882):

      • Became the standard for solidifying jelly due to its superior properties.

Introduction to Microbial Growth

  • Prokaryotic Diversity:

    • Thrive in extreme environments (ocean depths, volcanic vents, polar regions).

    • Study of these microbes offers insights into potential extraterrestrial life.

    • Growth requires specific nutrients and conditions for culture, highlighting both medical and industrial significance.

Principles of Bacterial Growth

  • Binary Fission:

    • Process by which prokaryotic cells divide.

    • Exhibits exponential growth; population doubles each division.

  • Generation Time:

    • Varies by species and environmental conditions.

    • Example: Foodborne pathogens can quickly multiply, from 10 cells to 40,960 in 4 hours under optimal conditions.

Growth Calculation

  • Formula: Nt = N0 x 2^n

    • Nt = final number of cells

    • N0 = initial number of cells

    • n = number of divisions

  • Example in potato salad shows emphasis on pathogen growth dynamics under optimal conditions.

The Power of Exponential Growth

  • Rapid Increase:

    • Optimal conditions can lead to enormous populations in short times.

    • Generation time is crucial in understanding microbial population dynamics.

Prokaryotic Growth in Nature

  • Adaptability:

    • Microbes in dynamic environments adjust via sensing changes.

    • They can live individually or within aggregates called biofilms.

Biofilm Formation

  • Process:

    • Planktonic (free-floating) bacteria adhere to surfaces.

    • Produce extracellular polymeric substances (EPS).

    • Channels form for nutrient and waste exchange.

    • Detachment and formation of new biofilms can occur.

Characteristics of Biofilms

  • Architecture:

    • Channels facilitate nutrient flow and waste disposal.

  • Significance:

    • Dental plaque and infections can stem from biofilms.

    • Industrial challenges with pipe clogging.

    • Protective structures make microbes more resistant to treatment.

Interactions in Mixed Communities

  • Cooperative Interactions:

    • Some species support each other’s growth; oxygen consumption by one helps anaerobes grow.

  • Competitive Interactions:

    • Species may produce toxins to inhibit others.

Obtaining a Pure Culture

  • Definition: A population derived from a single cell, essential for studying a specific microbial species.

  • Techniques:

    • Aseptic techniques to avoid contamination.

    • Use of culture media (broth or solid) that contains necessary nutrients.

Growing Microorganisms on Solid Medium

  • Essential to have the right conditions for individual cells to create visible colonies (~1 million cells).

  • Agar Properties:

    • Not destroyed by high temperatures, solidifies below 45°C.

    • Effective for isolating pure cultures.

Streak-Plate Method

  • Most common isolation technique.

  • Involves spreading cells to achieve separation and individual colonies.

Maintaining Stock Cultures

  • Streak-plate method allows pure cultures to be stored.

  • Can be kept in a refrigerator or frozen at -70°C for long-term study.

Prokaryotic Growth Conditions

  • Closed Systems:

    • Batch cultures with no nutrient renewal or waste removal.

  • Open Systems:

    • Continuous cultures that allow consistent nutrient addition and waste removal.

The Growth Curve

  • Stages:

    • Lag phase: no growth, metabolic preparation.

    • Log/exponential phase: rapid cell division.

    • Stationary phase: equilibrium between growth and death.

    • Death phase: viable cells decrease.

    • Prolonged decline: potential survival of some cells.

Colony Characteristics

  • Differences exist between colonies based on environmental conditions.

  • Outer edges have more nutrients and oxygen compared to the center.

Continuous Culture Systems

  • Chemostat: Device that maintains continuous growth through regulated nutrient input and waste removal.

Environmental Factors Influencing Growth

  • Extremophiles: Microbes thriving in harsh conditions.

  • Key Conditions: Temperature, atmosphere, pH, water availability.

Temperature Requirements

  • Each species has an optimal temperature range for growth:

    • Psychrophiles, psychrotrophs, mesophiles, thermophiles, hyperthermophiles.

Protein Thermostability

  • Thermophilic proteins resist denaturing, crucial for survival in high temperatures.

Oxygen Requirements

  • Reactive Oxygen Species (ROS):

    • Byproducts of aerobic respiration potentially harmful to cells.

    • Organisms have adapted mechanisms such as superoxide dismutase and catalase to mitigate damage.

pH Influence on Microbial Growth

  • Most microbes prefer neutral pH (around 7).

  • Microbial Adaptations: Neutrophiles, acidophiles, and alkaliphiles exist to thrive in varying pH levels.

Water Availability

  • Water is essential for microbial growth; solute concentrations can impact cell health.

  • Certain microbes thrive in high salt concentrations (halotolerant and halophiles), demonstrating varied survival strategies.