Key Concepts in Microscopic Organisms and Prokaryotes

Microscopic Organisms Overview

Classification of Microscopic Organisms
Divided into Prokaryotic and Eukaryotic:

Prokaryotes:

• Smaller, more primitive cells.

• Lack membrane-bound organelles.

• Example domains: Archaea and Bacteria.

Eukaryotes:

• Larger, more complex cells.

• Contain membrane-bound organelles.

• Domain: Eukarya.

8.2 Prokaryotic Structures and Properties

Cell Wall:

• Most prokaryotes have a protective cell wall, similar to plants.

• Provides stability in various environments, allowing them to withstand different conditions such as temperature and pH.

Motility:

• Many prokaryotes are motile, enabling them to move toward nutrients or away from harmful substances.

• Flagella: Tail-like structures used for propulsion; can vary in number and distribution.

Capsule:

• Some bacteria possess a sticky capsule that enhances protection against phagocytosis and allows attachment to surfaces, facilitating colonization.

Endospores:

• Certain prokaryotes can form endospores, which are highly resistant to extreme conditions such as heat, desiccation, and chemicals.

• Remains dormant until conditions are favorable for growth again, allowing survival in adverse environments.

Reproduction:

• Prokaryotes often reproduce through binary fission (splitting in half).

• Can lead to rapid population increase under favorable conditions, resulting in exponential growth.

Shapes of Prokaryotes:

• Cocci: Round cells (may be clustered or chained).

• Bacilli: Rod-shaped cells (may also be clustered or chained).

• Spiral: Curved or twisted, generally found singly.

8.2 Methods of Nutrition in Prokaryotes

Prokaryotes acquire food via various methods:

• Photosynthesis: Utilizes solar energy using pigment molecules like chlorophyll.

• Chemosynthesis: Utilizes chemical energy, such as from hydrogen sulfide or inorganic compounds.

• Heterotrophy: Consumes other organisms for nutrition; includes saprotrophs that decompose organic matter.

Biofilms

Definition:

• Organized colonies of prokaryotes attached to surfaces (e.g., plaque on teeth).

Characteristics:

• Biofilms can be beneficial, aiding in nutrient cycling, or harmful, causing infections.

• Example of harmful biofilm: urinary tract infections, middle-ear infections.

Maintenance Tip:

• It's advised to regularly clean pet water bowls to prevent biofilm buildup, which can lead to health issues.

8.3 Archaea: Extremophiles

Types of Archaea:

• Methanogens: Produce methane, found in anaerobic environments (e.g., swamps, digestive tracts).

• Halophiles: Thrive in high salt concentrations (e.g., Great Salt Lake, salt flats).

• Thermophiles: Prefer extreme heat above boiling temperatures (e.g., hot springs, deep-sea vents).

8.4 Bacteria in Our Environment

Habitats:

• Bacteria are common in diverse environments, including soil, water, and the human body, where they outnumber human cells significantly.

• Approximately 90% of cells in the human body are bacteria, playing essential roles in health.

Role of Bacteria:

• Helpful Bacteria:

  • Nitrogen-fixers: Convert atmospheric nitrogen into usable forms for plants, crucial for ecosystem functioning.

  • Decomposers: Break down dead organic matter and toxins, recycling nutrients back into the soil.

  • Probiotics: Aid in nutrient absorption and contribute to gut health, providing anti-inflammatory properties.

• Harmful Bacteria (Pathogens):

  • Cause various diseases (e.g., MRSA, Lyme disease, Salmonella) and foodborne illnesses.

8.5 Bacterial Reproduction and Gene Transfer

Chromosome and Reproduction:

• Bacteria typically have a single circular chromosome and reproduce asexually through binary fission.

• This method results in genetically identical cells within a colony, contributing to rapid population growth.

DNA Transfer Mechanisms:

• Transformation: Uptake of foreign DNA from the environment into a bacterial cell, allowing for genetic variation.

• Transduction: Bacteriophages transfer DNA between bacteria through infection, enabling genetic changes.

• Conjugation: DNA is transferred between bacteria via a physical bridge (sex pilus), facilitating horizontal gene transfer.

• Plasmid Transfer: Small, independent circular DNA (plasmids) can be shared between bacteria, allowing for various genetic adaptations, including antibiotic resistance.