Unit 3 Chapter 4 PT 1

Overview of Microbial Diversity

• Discussed the phylogeny and classification of microorganisms, focusing on bacterial and archaeal diversity.

Phylogenetics

• Phylogenetics Definition: Study of evolutionary history and relationships among groups of organisms.

• Determining Relationships: Various methods such as DNA sequencing, protein structure comparison, and morphological traits.

  • Methods:

    • DNA sequences

    • Specific proteins (amino acid sequences)

    • Morphology (physical characteristics)

    • Biochemical reactions

Domains of Life

• Three Domains: Bacteria, Archaea, Eukarya.

  • All domains converge to a point known as the LEUCA (Last Universal Common Ancestor).

• Prokaryotic Domains: Bacteria and Archaea are both prokaryotic, with Archaea more closely related to Eukarya.

Classification Systems

• Organism Grouping: Classification is based on traits like morphology, biochemical reactions, and genetic analysis.

  • Macroscopic Morphology: Appearance of colonies on agar (size, shape, color).

  • Microscopic Morphology: Shapes of cells (cocci, bacilli, spirochetes).

• Taxonomy: Science of classification, arranging close organisms into groups called taxa.

  • Developed by Carolus Linnaeus: Introduced binomial nomenclature (two names: genus and species).

  • Example of classification levels: domain, kingdom, phylum, class, order, family, genus, species.

Historical Changes in Classification

• Original Two-Kingdom System: Plantae and Animalia by Linnaeus.

  • 1866: Ernst Haeckel introduced Protista as a third kingdom as a catch-all.

• Kingdom Monera (for prokaryotes) introduced post-1950s.

• Five-Kingdom System: Developed by Robert Whittaker, examining nutrient acquisition methods, added Fungi as a distinct category.

• Three-Domain System: Introduced by Carl Woese in 1990, recognizing Archaea as distinct.

Identifying Bacteria

• Challenges: Prokaryotes don’t fossilize well leading to difficulties in classification.

• Important Methods:

  • Fatty Acid Composition: Was widely used in the past but less common now.

  • Phage Typing: Using bacteriophage to trace relationships based on infectivity.

  • Genetic Analysis: Looking at sequences of nucleotides to determine relationships.

Major Bacterial Groups and Characteristics

• Examples include:

  • Alpha Proteobacteria:

    • Rhizobium: Fixes nitrogen in plant root nodules, crucial for nitrogen cycle.

    • Bartonella henselae: Causes cat scratch disease; transmitted by scratches from cats.

    • Wolbachia: Infects arthropods, involved in reproductive strategies and may suppress mosquito populations.

  • Beta Proteobacteria:

    • Bordetella pertussis: Causes whooping cough, preventable by vaccine.

    • Neisseria meningitidis: Causes bacterial meningitis, vaccine available.

  • Gamma Proteobacteria:

    • Pseudomonas aeruginosa: Opportunistic pathogen, causes infections in immunocompromised individuals.

    • Legionella pneumophila: Acquired via water sources; not contagious.

    • Vibrio cholerae: Causes cholera via contaminated water and shellfish; leads to severe dehydration.

    • E. coli: Indicator of fecal contamination; some strains are pathogenic.

  • Salmonella: Causes gastroenteritis; typhoid fever is a severe form.

  • Yersinia pestis: Causes bubonic plague, spread by fleas; historically significant.

Conclusion

• Bacterial classification is essential for understanding microbial diversity and their interactions with environments and hosts.