Chapter 11 [Part 2/3] - Characterizing and Classifying Prokaryotes

Introduction to Bacteria

• Discussing the second part of Chapter 11, transitioning from Archaea to Bacteria.

• Focus on deeply branching organisms, phototrophic bacteria, and gram-positive organisms.

Phylogenetic Relationships

• Archaea as a distinct domain in phylogeny.

• Bacteria consist of various unique groups and categories.

Deeply Branching and Phototrophic Bacteria

Characteristics

• Represent primitive life forms, resembling early Earth conditions.

• Autotrophic, able to thrive in extreme environments.

Examples of Organisms

• Aquifex:

  • Chemoautotrophic, hyperthermophilic, and microaerophilic.

  • Derives energy from organic sources in hot habitats.

• Deinococcus:

  • Resilient against UV radiation, staining gram-positive despite similarities to gram-negative organisms.

  • Has pigments for lipid protection and DNA repair mechanisms; survives harsh conditions.

  • Notably sent into space and able to replicate upon return to Earth.

Phototrophic Bacteria

• Lack the complexity of eukaryotic photosynthesizers.

• Possess photosynthetic lamellae to aggregate pigments.

• Cyanobacteria:

  • Known as blue-green bacteria, integral to oxygenating prehistoric Earth.

  • Chlorophyll a as the primary pigment.

  • Predecessors to eukaryotic chloroplasts, capable of nitrogen fixation.

  • Utilize specialized cells, heterocysts, for anoxic nitrogen fixation and akinetes for survival in adverse conditions.

Other Types

• Green Sulfur & Non-Sulfur Bacteria:

  • Utilizes sulfur compounds for photosynthesis, inhabiting anaerobic environments.

  • Green sulfur bacteria deposit sulfur outside, while purple sulfur accumulate it internally.

Gram-Positive Bacteria

Overview

• Divided into low GC and high GC content groups.

Low GC Gram-Positive Bacteria

Groups

• Clostridia:

  • Rod-shaped obligate anaerobes, some forming endospores for survival.

  • Generators of significant toxins (e.g., tetanus, gangrene, botulism).

  • Importance in medical settings due to potential for severe infections.

• Mycoplasma:

  • Notable for lack of a cell wall, adopted a pleomorphic form.

  • Parasites that require host nutrients, associated with respiratory and urinary tract infections (e.g., Mycoplasma pneumoniae).

• Bacillus:

  • Soil-dwelling species, some pathogenic (e.g., Bacillus anthracis causing anthrax).

  • Contributors to antibiotic production and ecological balance (e.g., Bacillus thuringiensis).

Other Low GC Gram-Positives

• Listeria:

  • Capable of surviving in refrigerated conditions, risky for pregnant women.

• Lactobacillus:

  • Beneficial in food production and part of the healthy microbiome.

• Streptococcus, Staphylococcus, and Enterococcus:

  • Notable for pathogenicity and antibiotic resistance.

  • Streptococcus pneumoniae implicated in various diseases, including pneumonia.

  • Staphylococcus aureus as a common contaminant with MRSA concerns.

High GC Gram-Positive Bacteria (Actinobacteria)

• Rod-shaped and filamentous, some spore producers resembling fungi.

Key Genera

• Corynebacterium:

  • Example: Corynebacterium diphtheriae causes diphtheria, reduced incidence due to vaccination.

• Mycobacterium:

  • Thick cell wall from mycolic acid, slow growers, intracellular pathogens (e.g., Mycobacterium tuberculosis).

• Actinomyces:

  • Normal flora but can be pathogenic (e.g., Actinomyces israelii), some with ecological importance (e.g., Nocardia, Streptomyces).

Conclusion

• Overview of key characteristics and implications of gram-positive bacteria.

• Encouragement to explore additional resources and prepare for discussions on gram-negative organisms in the upcoming lecture.

Introduction to Bacteria

This section focuses on the transition from Archaea to Bacteria, particularly in the second part of Chapter 11. We will explore the diverse and complex world of Bacteria, highlighting deeply branching organisms, phototrophic bacteria, and the significant categories of gram-positive organisms.

Phylogenetic Relationships

• Archaea, recognized as a distinct domain in the tree of life, exhibit unique phylogenetic characteristics and evolutionary pathways.

• Bacteria comprise a multitude of distinct groups, each possessing unique features and ecological roles that contribute to the earth's biodiversity.

Deeply Branching and Phototrophic Bacteria

Characteristics

• Deeply branching bacteria are considered some of the most primitive life forms, closely resembling the conditions of early Earth, showcasing adaptations that suggest resilience and survival in harsh environments.

• These organisms are autotrophic, which means they can synthesize their own food and thrive in extreme conditions like high temperatures and pressures.

Examples of Organisms

• Aquifex:

  • A genus of bacteria that are chemoautotrophic, hyperthermophilic, and microaerophilic, often found in hot springs.

  • Aquifex bacteria derive energy from organic sources, utilizing chemical processes to sustain their metabolism in hot habitats, making them ideal subjects for studying life's origins.

• Deinococcus:

  • This genus is renowned for its remarkable resilience against UV radiation and various environmental stressors. Despite its staining as gram-positive, it shares many attributes with gram-negative organisms.

  • Deinococcus possesses specific pigments that aid in lipid protection, alongside advanced DNA repair mechanisms that allow it to survive extreme conditions. Notably, strains of this organism have been sent into space for experiments on radiation resistance and were able to replicate successfully upon return to Earth.

Phototrophic Bacteria

• Unlike eukaryotic photosynthesizers, phototrophic bacteria demonstrate a simpler structure and metabolic process.

• They possess photosynthetic lamellae that allow them to aggregate pigments for efficient light absorption and energy conversion.

Examples

• Cyanobacteria:

  • Often called blue-green bacteria, Cyanobacteria were instrumental in oxygenating our planet billions of years ago. As the first organisms to perform oxygenic photosynthesis, they played a critical role in shaping Earth's atmosphere.

  • They contain chlorophyll a, which is vital for photosynthesis, and they are considered the precursors to eukaryotic chloroplasts.

  • These bacteria are also capable of nitrogen fixation, a process that enriches soil fertility and supports plant growth. Specialized cells known as heterocysts facilitate anoxic nitrogen fixation, while akinetes help the organism survive adverse environmental conditions.

Other Types of Phototrophic Bacteria

• Green Sulfur and Non-Sulfur Bacteria:

  • These bacteria utilize sulfur compounds for photosynthesis, primarily inhabiting anaerobic environments.

  • Green sulfur bacteria are characterized by depositing sulfur externally, whereas purple sulfur bacteria accumulate it internally, which is significant for their energy production processes.

Gram-Positive Bacteria

Overview

• Gram-positive bacteria are classified primarily on the basis of their cell wall composition, which is categorized into low GC and high GC content groups. Their thick peptidoglycan layers make them easily distinguishable under a microscope.

Low GC Gram-Positive Bacteria

Notable Groups

• Clostridia:

  • A group of rod-shaped obligate anaerobes, some of which can form endospores that enable them to survive hostile environments.

  • Clostridia species are significant in medical settings due to their potential to generate severe toxins, causing diseases such as tetanus, gangrene, and botulism.

• Mycoplasma:

  • Mycoplasma are unique for their absence of a cell wall, leading to a pleomorphic morphology, adapting to various host environments.

  • As parasites, they rely on host nutrients and are often linked to respiratory and urinary tract infections, with Mycoplasma pneumoniae being a well-known pathogen.

• Bacillus:

  • This genus comprises soil-dwelling species, with some being pathogenic, like Bacillus anthracis, known to cause anthrax.

  • Additionally, some Bacillus species contribute to antibiotic production (e.g., Bacillus thuringiensis) and play a crucial role in maintaining ecological balance.

Other Low GC Gram-Positives

• Listeria:

  • Notable for their ability to survive in refrigerated foods and pose risks for vulnerable populations, such as pregnant women, leading to foodborne illnesses.

• Lactobacillus:

  • Beneficial bacteria involved in food production processes, such as yogurt fermentation, and play an essential role in maintaining a healthy microbiome.

• Streptococcus, Staphylococcus, and Enterococcus:

  • These genera are noted for their pathogenicity and emerging antibiotic resistance. Notably, Streptococcus pneumoniae is implicated in diseases including pneumonia.

  • Staphylococcus aureus is frequently found in contaminated environments and is known for its connection with MRSA (methicillin-resistant Staphylococcus aureus).

High GC Gram-Positive Bacteria (Actinobacteria)

• These include rod-shaped and filamentous bacteria, with some capable of producing spores, notably resembling fungi. Their diverse metabolic capabilities allow them to inhabit various ecosystems.

Key Genera

• Corynebacterium:

  • An important genus, with Corynebacterium diphtheriae being the causative agent of diphtheria, a disease that has seen reduced incidence due to effective vaccination.

• Mycobacterium:

  • Known for its distinctive thick cell wall composed of mycolic acid, resulting in slow growth and significant clinical importance due to its intracellular pathogenicity (e.g., Mycobacterium tuberculosis causing tuberculosis).

• Actinomyces:

  • This genus represents normal flora but includes pathogenic species like Actinomyces israelii and holds ecological importance in soil health, contributing to nutrient cycling (e.g., Nocardia, Streptomyces species).

Conclusion

This chapter offers an overview of the key characteristics, diversity, and implications of gram-positive bacteria. Students are encouraged to explore additional resources and prepare for engaging discussions on gram-negative organisms in the upcoming lecture.