Prokaryotes: Bacteria and Archaea

Chapter 22: Prokaryotes: Bacteria and Archaea

  • Overview:

    • Prokaryotes include bacteria and archaea.

    • They thrive in extreme conditions.

The 3 Domains of Life

  • Domains: Eukarya, Bacteria, Archaea.

  • Organisms in Eukarya include:

    • Land plants

    • Dinoflagellates

    • Green algae

    • Forams

    • Ciliates

    • Diatoms

    • Red algae

    • Cellular slime molds

    • Amoebas

    • Animals

    • Fungi

  • Archaea Examples:

    • Sulfolobus (thermophiles)

    • Halophiles

    • Methanobacterium

  • Bacteria Examples:

    • Spirochetes

    • Chlamydia

    • Cyanobacteria

    • Green sulfur bacteria

Introduction to Prokaryotes

  • Characteristics: Prokaryotes are single-celled organisms without a nucleus.

  • They reproduce asexually, primarily through binary fission.

  • First organisms on Earth 3.5-3. BYA

  • Live on and in every other living organism

  • most are benign (not causing 99% disease) and many are essential to all life, > 1% are pathogenic

  • Prokaryotic cells took a long time to be discovered because they are so small.

  • Leeuwenhoek had to first invent the microscope and see bacteria in 1670, which marked a significant milestone in microbiology as he was the first to observe and describe these microscopic organisms.

Historical Context of Microbiology

  • Koch's Postulates:

    1. A microorganism must be found in abundance in organisms suffering from the disease but should not be present in healthy organisms.

    2. The microorganism must be isolated from a diseased organism and grown in pure culture.

    3. The cultured microorganism should cause disease when introduced into a healthy organism.

    4. The microorganism must be re-isolated from the inoculated, diseased experimental host and identified as identical to the original specific causative agent.

  • helped establish germ theory- A: particular organisms cause a particular disease

  • Pure culture: a laboratory culture containing a single species of microorganism

  • Culture medium: contains all the nutrients needed by the target microorganism

  • Streptococcus Example: Demonstrates the adherence of Koch's postulates.

  • Gram staining: A method used to classify bacteria based on their cell wall composition, aiding in the identification and treatment of bacterial infections.

  • Cell structure; all cells have four common structures:

  1. the plasma membrane functions as a barrier for the cell and separates the cell from its environment

  2. The cytoplasm: a complex solution of organic molecules and salts inside the cell

  3. a double-stranded DNA genome(RNA genome in virus) : the informational archive of the cell

  4. Ribosomes(prokaryotic and eukaryotic ribosomes have the same function but different sizes): sites of protein synthesis.

Prokaryotic Structure 4

  • Cell walls

  • - lies outside the plasma membrane

  • protects and prevents cell lysis (rupture)

  • Bateria: w/ peptidoglycan (PG)

  • archea w/ other structural polysaccharides so not have peptidoglycan

  • Mycoplasmas have no cell walls

Gram positive bacteria

(thick PG layer) retain the crystal violet stain during Gram staining, appearing purple under a microscope, whereas Gram negative bacteria (thin PG layer and outer membrane) do not retain the stain and appear pink.

Gram negative bacteria

possess a more complex cell structure and are typically more resistant to antibiotics due to their outer membrane barrier.

Prokaryote Structure 5

  • Many have. a capsule or slime layer > glycocalyx, which provides additional protection and helps in adhering to surfaces.

  • Stucky carbs and proteins secreted outside cell wall: the most outer layer

Prokaryote Structure 6

  • Some have hair-like protein fimbriae (short pili)

  • helps cells stick to surfaces and each other (biofilms: resistant to anti-biotics, cleansers, and mechanical scraping)

  • Mant can form sex pili (transfer DNA which gives genes and genetic material)

  • Many have flagellum structure

  • Not homologous to eukaryote flagellum ( genes are completely different, or analogous)

  • ALLOWS MOVEMENT

Structure 8

  • Many prokaryotes have plasmids:

  • extra tiy DNA rings w/ few genes

  • replicate independently of the host chromosomes

  • not essential for life, but adds diversity (survival advantages)

Prokaryote Structure

  • Common Characteristics:

    • Often occur in aggregates: pairs, chains, clusters.

  • Plasmids: Extra small DNA rings that replicate independently; not essential for life but provide advantages such as drug resistance.

Differences Between Bacteria and Archaea

  • Differences fundamentally in:

    1. Plasma membranes (different lipid structures)

    2. Cell walls (Bacteria have peptidoglycan; Archaea do not)

    3. DNA replication (different mechanisms)

    4. Gene expression (varies significantly)

  • 16S rRNA sequencing (ribosomal) : Provides a molecular way to differentiate these domains.

Prokaryotic Diversity

  • Types of Prokaryotes:

    • Bacteria:

    • Examples include:

      • Proteobacteria (Gram-negative, diverse metabolism)

      • Chlamydias (obligate endoparasites)

      • Spirochetes (notable morphology, distinct movement)

      • Cyanobacteria (photosynthetic)

    • Archaea:

    • Includes extremophiles (thermophiles and halophiles).

    • Non-pathogenic to humans.

    • keep membrane stable in high heat salts, etc.Their unique lipid composition allows them to thrive in harsh environments, playing crucial roles in nutrient cycling and biogeochemical processes.

  • Plasma membrane

  • baacterial lipids are unbranched

  • use ester bonds

  • rchaean membranes are formed on glycerol skeleton with ether linkages (not ester)

  • hydrocarbons may be branched or have rings

  • Tetraether polymer allows extremophiles to withstand high temperatures. (ex: thermophile)]

Symbiosis two species living in a close relationship (free living = not living in symbiosis)

parasitism

  • smaller parasite benefits at the expense of other species (host)

  • including pathogens ( cause disease)

  • ex. anthrax, cholera bacteria (human pathogen cholera)

Commensalism

  • One specific benefit without any impact (good or bad) on other species

  • ex: most bacteria on our skin (bacteria in the gut)

Mutualism

  • both species benefit from each other

  • ex: Rhizobium in legume roots get sugar and water; provide fixed N for the plant

Prokaryote Metabolic and Ecological Diversity 4

  • Chemoheterotrophic bacteria are the most important decomposers on earth

  • secreted enzymes hydrolyze dead material or wastes

  • absorptive: monomers ( individual amino acids, nucleic acids) enter by diffusion/active transport

  • metabolism releases CO2 and N, P, K, etc.

Prokaryotes in the Environment

  • Carbon Cycle:

    • Prokaryotes play a significant role in carbon cycling through processes like carbon fixation (making sugar).

    • important base of aquatic food webs

  • Nitrogen Cycle:

    • Key roles by prokaryotes include nitrogen fixation, nitrification, and denitrifying bacteria.

    • Done over fertilization

    • completed by other prokaryotes in soil

  • Prokaryote Genetic Diversity

Pathogenic Bacteria

  • Types of Toxins:

    • Exotoxins: Secreted by bacteria (e.g., Clostridium tetani).

    • Endotoxins: Part of the outer membrane of Gram-negative bacteria (e.g., Salmonella).

  • Antibiotics: Target bacterial cells without harming eukaryotic cells (e.g., penicillin affects peptidoglycan in the cell wall).

Beneficial Prokaryotes

  • Applications:

    • In DNA technology and genetic engineering.

    • extremophiles: bacteria and archea that are adapted to grow under extreme conditions

    • Used in commercial production of chemicals and enzymes.

    • Food production: yogurt and cheese (e.g., Lactobacillus bulgaricus).

    • Microbial remediation: Certain bacteria can detoxify pollutants, remove heavy metals.

Conclusion

  • Endospores: Under stress conditions, some bacteria can form dormant endospores, which can survive extreme conditions, e.g., Bacillus anthracis and Clostridium tetani.

  • Among the vast diversity of prokaryotes, significant interactions with ecosystems and human health are noted, revealing their vital roles in both pathogenic and beneficial aspects.