Prokaryotes: Domain Bacteria and Cyanobacteria Lab 13

Prokaryotes: Domain Bacteria

Introduction to Domain Bacteria

The Domain Bacteria comprises the majority of prokaryotic organisms, commonly referred to as "true bacteria." These organisms are characterized by their lack of a membrane-bound nucleus and organelles, and their cell size typically ranges from 1 to 10 micrometers. Bacteria exhibit a wide variety of shapes, metabolic strategies, and ecological roles.

• Definition: Bacteria are single-celled prokaryotic organisms with cell walls, lacking a true nucleus and membrane-bound organelles.

• Examples: Escherichia coli, Bacillus subtilis, Staphylococcus aureus

• Applications: Bacteria are used in biotechnology, medicine, and environmental processes such as decomposition and nutrient cycling.

Heterotrophic Bacteria

Heterotrophic bacteria obtain energy by consuming organic matter. Many act as decomposers, breaking down dead organisms and recycling nutrients in ecosystems. Some are pathogenic, causing diseases in plants, animals, and humans.

• Definition: Heterotrophs are organisms that obtain energy by consuming organic compounds produced by other organisms.

• Decomposers: Bacteria that break down dead organic material, returning nutrients to the environment.

• Pathogens: Disease-causing bacteria, such as Streptococcus pyogenes (causes strep throat).

• Cell Wall Composition: Most bacteria possess a cell wall made of peptidoglycan, a polymer of sugars and amino acids.

Bacterial Shapes and Classification

Bacteria are classified based on their shapes and arrangements. The three main shapes are:

• Coccus (spherical)

• Bacillus (rod-shaped)

• Spirillum (spiral-shaped)

These shapes can be observed under a compound microscope at magnifications of 100X, 400X, and 1000X.

Laboratory Techniques: Using High-Power Objectives

Microscopy is essential for studying bacteria due to their small size. High-power objectives (such as 1000X) are used to view individual cells and their structural characteristics.

• Procedure: Begin with 40X magnification, then increase to 400X and 1000X to observe details.

• Oil Immersion: Used with 1000X objective to improve resolution.

• Staining: Techniques such as Gram staining help differentiate bacterial types.

Examples of Heterotrophic Bacteria

• Streptococcus pyogenes: Pathogen causing strep throat and skin infections.

• Lactobacillus: Used in yogurt and sauerkraut production; ferments sugars to lactic acid.

• Spirillum: Spiral-shaped bacteria found in aquatic environments.

• Bacillus endospores: Rod-shaped bacteria that form resistant spores.

• Escherichia coli: Common gut bacterium, model organism in molecular biology.

Cyanobacteria

Introduction to Cyanobacteria

Cyanobacteria, also known as "blue-green algae," are photosynthetic prokaryotes found in aquatic and terrestrial environments. They are important primary producers and contribute to oxygen production.

• Definition: Cyanobacteria are photosynthetic bacteria that contain chlorophyll a and phycobilins.

• Role: Major contributors to global photosynthesis and oxygen production.

• Example: Anabaena, Nostoc, Oscillatoria

Photosynthetic Pigments and Metabolism

Cyanobacteria possess pigments such as chlorophyll a and phycobilins (phycocyanin and phycoerythrin) that enable photosynthesis. They can fix atmospheric nitrogen in specialized cells called heterocysts.

• Photosynthesis Equation:

$6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2$

• Nitrogen Fixation: Conversion of atmospheric nitrogen ($N_2$) to ammonia ($NH_3$) in heterocysts.

• Oxygen Sensitivity: Nitrogenase enzyme is inhibited by oxygen; heterocysts provide a low-oxygen environment.

Common Cyanobacteria Genera

• Gloeocapsa: Found in stagnant water; cells surrounded by a thick jelly-like sheath.

• Oscillatoria: Filamentous cyanobacteria; move by oscillating motion.

• Nostoc: Forms large colonies of trichomes; contains heterocysts for nitrogen fixation.

• Anabaena: Responsible for algal blooms; forms chains of cells and heterocysts.

Laboratory Observation of Cyanobacteria

Cyanobacteria can be observed at 100X and 400X magnification. Identification is based on colony shape, presence of heterocysts, and filament structure.

Table: Comparison of Bacterial Types

Type	Cell Shape	Metabolism	Special Features	Examples
Heterotrophic Bacteria	Coccus, Bacillus, Spirillum	Decomposition, fermentation, pathogenicity	Peptidoglycan cell wall, endospore formation	Streptococcus, Lactobacillus, Bacillus
Cyanobacteria	Filamentous, colonial, unicellular	Photosynthesis, nitrogen fixation	Chlorophyll a, phycobilins, heterocysts	Anabaena, Nostoc, Oscillatoria

Summary

Prokaryotes in the Domain Bacteria and Cyanobacteria exhibit diverse shapes, metabolic strategies, and ecological roles. Understanding their structure and function is essential for studies in microbiology, ecology, and biotechnology.