Bacterial Phyla and Evolutionary Relationships

Evolutionary Relatedness and Bacterial Phyla

• Evolutionary relationships in bacteria are measured by comparing 16S rRNA gene sequences; sequence differences indicate divergence time from a common ancestor.
• Approximately 30 bacterial phyla are culturable in labs, but estimates suggest over 1,000 possibly undiscovered phyla.
• Seven major phyla are significant for human health and ecosystems.

Firmicutes and Actinobacteria

• Firmicutes, characterized by thick cell walls, include species such as Clostridium that produce dormant, resistant endospores.
• Endospores withstand extreme conditions: heat, desiccation, radiation, and chemicals.
• Sporulation occurs under nutrient scarcity, leading to a unique cell division where the polar compartment becomes a forespore.
• Actinobacteria, including Streptomyces, produce antibiotics and grow as radial filaments; they have a thick waxy coat and high G+C content.

Proteobacteria

• A diverse group, including heterotrophs, lithotrophs, and photosynthetic species; all are Gram-negative.
• Proteobacteria possess an outer membrane loaded with receptor proteins and lipopolysaccharides (LPS), which can be toxic.
• Enterobacteriaceae, a family within Proteobacteria, contains rod-shaped bacteria like Escherichia coli and Proteus mirabilis, known for their roles in human infections.

Bacteroidetes

• Consist of Gram-negative anaerobic rods, crucial for gut health but can also cause abscesses post-surgery, e.g., Bacteroides species.

Spirochaetes

• Feature distinctive coiled shapes and periplasmic flagella; include both symbiotic (e.g., in termites) and pathogenic types (e.g., Borrelia burgdorferi, which causes Lyme disease).

Chlamydiae

• Obligate intracellular pathogens, grow as inclusion bodies within host cells, causing diseases like pneumonia and sexually transmitted infections.
• These bacteria alternate between elementary bodies (infectious form) and reticulate bodies (non-infectious, metabolically active).

Pathogen Evolution Factors

• Pathogens evolve in three primary environments: zoonotic hosts, sheltered species, and natural environments.
• Zoonotic hosts can share pathogens with humans, facilitating genetic recombination that allows new infections to emerge.
• Sheltered species provide environments for bacterial evolution and genetic exchange.
• Natural environments serve as genetic melting pots where genes related to antibiotic resistance often originate.

Selected Pathogens

• Firmicutes examples:
  • Bacillus anthracis causes anthrax.
  • Clostridium difficile leads to intestinal diseases, especially in antibiotic-treated patients.
  • Clostridium botulinum produces botulinum toxin (Botox) and can cause botulism.
  • Clostridium tetani is responsible for tetanus.

Non-Spore Formers and Their Impact

• Enterococcus spp. are intestinal microbiota that can cause severe infections, especially in immunocompromised individuals, and are treated with Vancomycin.
• Lactobacillus and Lactococcus spp. are important in dairy culture, fermenting lactose to produce yogurt and cheese.

Key Characteristics of Proteobacteria

• Classified by diverse metabolic pathways and Gram-negative structure.
• Most bacteria in this phylum can cause infections, with some forming biofilms contributing to increased antibiotic resistance.

Conclusion

• Understanding bacterial diversity offers insights into health, ecology, and evolutionary biology.
• Awareness of how these bacteria evolve and interact with their environments is crucial for managing infections and developing treatments.

This quiz explores the evolutionary relatedness of bacteria through comparisons of 16S rRNA gene sequences and examines major bacterial phyla. Key phyla such as Firmicutes and Actinobacteria are highlighted for their significance in human health and ecosystems. Test your knowledge on bacterial diversity and characteristics!