6_Archaea_and_Bacteria_Jan_30

Chapter 27: Archaea and Bacteria

Key Concepts

• Diversity and Evolution

• Structure and Movement

• Reproduction

• Nutrition and Metabolism

• Ecological Roles and Biotechnology Applications

Diversity and Evolution

• Both Domain Archaea and Domain Bacteria (Eubacteria) are classified as prokaryotic organisms, which means they lack a true nucleus.

• There exists vast diversity within and between these domains, contributing to various ecological niches and functions.

Features of Domain Archaea

• Archaea share features with eukaryotic cells, indicating a possible common ancestry, including:

  • Histone proteins and ribosomal proteins.

• Unique membrane lipids contribute to resilience in harsh environments, notably ether-bonded lipids which are more resistant to heat.

• Archaea often inhabit extreme environments as extremophiles, though many thrive in moderate conditions as well.

Types of Extremophiles

• Halophiles: Thrive in high salt concentrations; for example, Halobacterium found in the Great Salt Lake.

• Hyperthermophiles: Can withstand high temperatures; for instance, Methanopyrus at deep-sea thermal vents.

• Acidophiles: Live in acidic environments; Sulfolobus grows in acidic hot springs with a pH below 3.

Important Phyla of Archaea

• Phylum Thaumarchaeota: Vital to the nitrogen cycle through nitrification, converting ammonium to nitrate.

• Phylum Euryarchaeota: Includes methanogens that produce methane, playing a significant role in the carbon cycle.

Differences Between Archaea and Bacteria

• Peptidoglycan is a distinguishing component of bacterial cell walls, whereas Archaea may utilize proteins.

• The plasma membrane composition differs significantly, with bacteria using unbranched fatty acids connected by ester bonds and Archaea employing branched isoprene chains with ether bonds.

Domain Bacteria Overview

• Bacteria consist of approximately 50 known phyla, with many structural and metabolic features yet to be discovered.

• While most bacteria thrive in moderate conditions, some can be extremophiles and form symbiotic relationships with eukaryotic organisms, such as the phycosphere surrounding algae or cyanobacteria.

Notable Bacterial Phyla

• Proteobacteria:

  • Includes alpha, beta, gamma, and epsilon subclasses; encompasses many important pathogens like Escherichia coli and Helicobacter.

• Cyanobacteria: Photosynthetic bacteria that produce oxygen and are essential in producing organic carbon.

Cyanobacteria Diversity and Impact

• They exhibit significant structural diversity and can exist as unicells, colonies, or filaments.

• Essential ecological roles include nitrogen fixation and organic carbon production.

• Some strains can produce toxic metabolites, leading to harmful cyanobacterial blooms causing water quality degradation.

Horizontal Gene Transfer

• This genetic exchange contributes significantly to diversity in microbes; substantial genes in some bacteria, such as E. coli, come from horizontal transfer.

Structure of Bacteria and Archaea

• Generally small in size (under 1-15 micrometers), allowing rapid cell division.

• Thylakoids increase surface area for photosynthesis, particularly in cyanobacteria, where chlorophyll and phycobilins are involved in light harvesting.

• Magnetosomes help organisms locate low-oxygen habitats using magnetite crystals.

• Structures like gas vesicles aid buoyancy in aquatic environments.

Cell Shape and Wall Structure

• Bacteria can be categorized by shapes:

  • Cocci (spherical), Bacilli (rod-shaped), Vibrios (comma-shaped), Spirochaetes (flexible spiral), and Spirilla (rigid spiral).

• Most bacteria possess a rigid cell wall primarily comprised of peptidoglycan, with variations in thickness affecting their susceptibility to antibiotics.

Motility

• Various forms of movement include swimming via flagella, twitching or gliding through pili, and adjusting buoyancy with mechanisms such as gas vesicles.

Reproduction

• Binary fission is the primary method of reproduction, crucial for microbial counting and detection in laboratory settings.

• Example question: If 10 colonies arise from plating 0.1 mL of a water sample, the concentration is calculated as 100 bacteria/mL.

Survival Mechanisms

• Akinetes are specialized cells within certain cyanobacteria that store nutrients and survive adverse conditions, effectively allowing population recovery.

• Endospores are another survival mechanism, found in some Gram-positive bacteria, providing resilience against extreme conditions.

Nutrition and Metabolism

• Microbial metabolism showcases unparalleled diversity, categorized by energy and carbon source.

• Autotrophs can produce their own organic compounds, including photoautotrophs (using sunlight) and chemoautotrophs (utilizing inorganic compounds).

• Heterotrophs require organic compounds, with photoheterotrophs using light for energy but needing organic substances, while chemoheterotrophs derive energy and carbon from organic sources.

Ecological and Biotechnological Roles

• Bacteria and Archaea play essential roles in elemental cycling (e.g., carbon, nitrogen), exhibiting mutualistic associations such as those between Rhizobium and legumes.

• They also contribute to biotechnological advances, with many antibiotics derived from bacterial secondary metabolites.

Nitrogen Fixation

• Cyanobacteria can fix atmospheric nitrogen through specialized processes that protect nitrogenase enzymes from oxygen exposure, employing strategies such as spatial separation (heterocysts) and temporal separation (night fixation).

Conclusion

Understanding the characteristics, diversity, and ecological roles of Archaea and Bacteria underscores their significance in both biological systems and biotechnological applications.