bacterial growth with bacteriophages (1)

Domain Bacteria: Masters of Every Environment

  • Bacteria exist in staggering numbers and a wide range of habitats.

  • Human gut microflora contains 600 species of bacteria, with a quarter of feces by weight consisting of bacteria.

  • Importance of gut bacteria highlighted despite seeming unpleasant ("YUCH!").

Characteristics of Bacteria: As Prokaryotes

  1. Prokaryotic Structure:

    • No membrane-bound organelles (e.g. nucleus, vacuoles, mitochondria, chloroplasts).

    • Contains ribosomes (comprised of RNA).

    • DNA is arranged as a single chromosome with additional circular DNA (plasmids).

Bacterial Cell Structure

  • Components of a bacterial cell include:

    • Prokaryotic nature

    • Plasmids

    • Cytoplasm

    • Pilus (attachments for movement and adherence)

    • Bacterial flagellum (for motility)

    • Capsule (protective outer layer)

    • Ribosomes

    • DNA

    • Plasma membrane

    • Cell wall (provides structure and protection)

Oxygen Requirements for Bacteria

  • Anaerobic Bacteria:

    • Do not require oxygen, can die in its presence (Obligate Anaerobes).

    • Example: Tetanus; caution advised regarding honey for infants due to risk of tetanus.

  • Facultative Anaerobes:

    • Can survive with or without oxygen (e.g. E. coli).

    • Prefer absence of oxygen for optimal survival.

  • Aerobic Bacteria:

    • Require oxygen for survival (Obligate Aerobes).

    • Example: Tuberculosis bacterium.

Nutrition in Bacteria

  • Autotrophs:

    • Transform sun or chemical energy into food.

    • Photoautotrophs: use light energy and CO2 to create organic compounds (similar to plants).

    • Chemoautotrophs: utilize bond energy from inorganic compounds (e.g. hydrogen sulfide) to fixed carbon dioxide.

  • Majority are Heterotrophs.

    • Examples include E. coli, spirillum, anthrax.

Reproduction in Bacteria

  • Primarily asexual, through binary fission.

    • Results in daughter cells genetically identical to parent cells (no genetic variation).

  • Bacteria are unicellular but can form colonies, visible as dots on a culture plate.

  • Biofilms can form complex colonies with diverse types of bacteria.

Reproductive Cycles

  • Exponential Growth: Rapid increase in bacterial numbers under optimal conditions (favorable environments and resources).

  • Logistic Growth: Growth rate that decreases as resources become limited.

Sexual Reproduction in Bacteria

  • Can transfer DNA through mechanisms such as:

    • Uptaking DNA from live bacteria.

    • Picking up DNA from dead bacteria.

    • Virus-mediated DNA transfer.

  • Results in genetic variation among bacterial populations.

Optimal Growth Conditions for Bacteria

  • Essential conditions for ideal bacterial growth include:

    • Sufficient food source.

    • Optimal temperature: human pathogens thrive best at ~37°C (98.6°F).

    • Presence of moisture, preferably in darkness.

    • Oxygen level considerations (aerobic vs anaerobic requirements).

Competition with Bacteria for Food

  • Bacteria compete with humans for available food sources.

  • Preservation techniques against bacterial growth include:

    • Salting

    • Freezing

    • Refrigeration

    • Drying (e.g. prunes)

    • Pickling

Antibiotics and Disease-Causing Bacteria

  • Antibiotics combat harmful bacteria.

    • Most derived from fungi, competing for the same ecological niches.

    • Must exploit differences in bacterial vs human cell biology to minimize harm.

  • Example: Penicillin destroys bacterial cell walls without affecting animal cells.

Bacterial Targets for Antibiotics

  • Current antibiotics target various aspects of bacterial biology:

    • Cell wall synthesis (e.g. penicillins, vancomycin).

    • DNA replication (e.g. quinolones).

    • RNA polymerase and folic acid synthesis.

    • Protein synthesis at ribosomes with different inhibitors.

Antibacterial Agents in Action

  • Antibacterial agents create zones of inhibition in culture tests to evaluate effectiveness:

    • Larger zones indicate more effective antibiotics.

Endospore Production in Bacteria

  • Endospore formation allows bacteria to survive harsh conditions;

  • It’s not a reproduction method but a survival strategy.

Harmful Bacteria Forming Endospores

  • Examples of harmful bacteria that produce endospores:

    • Clostridium tetani (tetanus)

    • Clostridium botulinum (deadly food poisoning)

Beneficial Bacteria

  • Many bacteria are beneficial for humans:

    • Intestinal bacteria aid in digestion and synthesis of vitamins.

    • Probiotics marketed to enhance gut bacteria.

    • Appendix serves as a reservoir for beneficial bacteria.

Uses of Bacteria in Foods

  • Bacteria used in producing various foods, such as cheeses and fermented products (e.g. yogurt).

Medical and Environmental Applications of Bacteria

  • Genetic engineering uses bacteria to produce medical products (e.g. insulin).

  • Environmental remediation employs bacteria to clean up pollutants and treat waste.

Viruses: Overview

  • Viruses are acellular entities that require a living host to reproduce.

    • Components include capsid (protein shell) and nucleic acid core (DNA or RNA).

    • May have lipid envelopes and surface spikes for host attachment.

Types of Viruses and Their Reproductive Cycles

  • Viruses are host-specific:

    • Bacteriophages infect bacteria via lytic or lysogenic cycles.

    • Animal viruses include influenza and HIV;

    • Plant viruses, such as tobacco mosaic virus.

Viruses' Reproductive Cycle

  • Lytic Cycle:

    • Involves direct takeover of host machinery to replicate and cause cell lysis.

  • Lysogenic Cycle:

    • Viral DNA integrates into host DNA and can be replicated along with bacterial division.

Differences in Viral Life Cycles

  • Lytic Cycle: Rapid attack and destruction of host cells.

  • Lysogenic Cycle: Prolonged phase where viral DNA is replicated with the host genome.