Understanding Monera: Characteristics, Types, and Importance
Monera
General Characteristics
- Cosmopolitan distribution (found everywhere)
- Prokaryotic cells (lack true nucleus and membrane-bound organelles)
- Circular DNA
- Rigid cell wall
- Heterotrophic (most species) and some autotrophic
- Vegetative and asexual reproduction
- Decomposers, contributing to soil fertility
Types of Monera
1. Archaebacteria (Ancient Bacteria)
2. Eubacteria (True Bacteria)
- Bacteria
- Cyanobacteria
Bacteria
Discovery and History
Bacteria were first discovered by Anton Van Leeuwenhoek in 1675. Ehrenberg coined the term “bacterium” in 1828. Louis Pasteur (1864) and Robert Koch (1876), the father of bacteriology, later established their disease-causing abilities.
Distribution and Size
Bacteria are ubiquitous, thriving in diverse environments from water bodies to soil and even extreme temperatures. Their microscopic size typically ranges from 0.5µ to 1.5µ in diameter.
Shape and Classification
Bacteria exhibit various shapes and are classified accordingly:
A) Coccus Bacteria (Spherical)
- Monococcus (single): e.g., Micrococcus
- Diplococcus (pairs): e.g., Pneumonia
- Tetracoccus (groups of four): e.g., Tetracoccus cechi
- Streptococcus (chains): e.g., Streptococcus
- Staphylococcus (clusters): e.g., Staphylococcus sps.
- Sarcina (cubical packets)
B) Bacillus Bacteria (Rod-shaped)
- Monobacillus (single): e.g., Lactobacillus
- Diplobacillus (pairs): e.g., Morexella
- Streptobacillus (chains): e.g., Streptobacillus
- Palisade (stacks): e.g., Corynebacterium
C) Helical Bacteria (Coiled or Twisted)
- Spiral bacteria: e.g., Spirillum volutans
- Vibrio (comma-shaped): e.g., Vibrio cholerae
D) Filamentous Bacteria (Thread-like): e.g., Streptomyces
Flagellation
Flagella, protein-based appendages, facilitate locomotion in liquid environments. Their arrangement and number categorize bacteria into various groups (atrichous, monotrichous, amphitrichous, cephalotrichous, lophotrichous, peritrichous).
Cell Envelope
The cell envelope, comprising the plasma membrane and cell wall, provides structural integrity and protection against internal pressure. Peptidoglycans, unique to bacterial cell walls, contribute to rigidity and shape. The presence or absence of peptidoglycans differentiates Gram-positive and Gram-negative bacteria.
Other Structures
- Chromatophores: Single-membrane vesicles containing photosynthetic pigments in photosynthetic bacteria.
- Pili: Protoplasmic outgrowths aiding in attachment during reproduction.
Staining Techniques
The Gram staining technique, developed by Christian Gram in 1884, differentiates bacteria based on their cell wall properties into Gram-positive (retain blue color) and Gram-negative (do not retain blue color).
Nutrition
Bacteria exhibit diverse nutritional modes:
A) Autotrophic Bacteria (Synthesize their own food)
- Photosynthetic Bacteria: Utilize light energy, pigments, and inorganic compounds for food production. Examples include green sulfur bacteria, purple sulfur bacteria, and non-sulfur bacteria.
- Chemosynthetic Bacteria: Obtain energy by oxidizing inorganic substances like ammonia, nitrite, hydrogen, sulfur, and iron. Examples include sulfur bacteria, hydrogen bacteria, iron bacteria, and nitrifying bacteria.
B) Heterotrophic Bacteria (Obtain food from external sources)
- Parasitic Bacteria: Derive nourishment from living hosts, causing diseases (pathogenic) or remaining harmless (non-pathogenic).
- Symbiotic Bacteria: Engage in mutually beneficial relationships with other organisms.
- Saprophytic Bacteria: Decompose dead organic matter.
Respiration
Based on oxygen requirements, bacteria are classified as:
- Aerobic Bacteria: Require oxygen for survival.
- Anaerobic Bacteria: Survive in the absence of oxygen.
- Facultative Bacteria: Can survive with or without oxygen.
Economic Importance of Bacteria
- Enhance soil fertility through nitrogen fixation.
- Used in industrial processes for producing dairy products, organic acids, alcohols, and vitamins.
- Act as decomposers in ecosystems.
- Used in bio-mining for metal extraction.
- Can cause diseases in plants and animals.
- Contribute to food spoilage.
- Used in the production of enzymes and vaccines.
Cyanobacteria (Blue-Green Algae)
- Cosmopolitan distribution.
- Prokaryotic cells with cell walls containing peptidoglycan, cellulose, hemicellulose, and pectin.
- Perform oxygenic photosynthesis.
- Possess specialized cells called heterocysts for nitrogen fixation.
- Lack flagella.
- Reproduce asexually and, in some cases, sexually.
Nostoc (A type of Cyanobacteria)
Nostoc forms colonies in freshwater and damp soil, often living symbiotically with other organisms. Its filamentous structure consists of vegetative cells, heterocysts, and akinetes (resting spores).
Reproduction in Nostoc
Nostoc reproduces vegetatively through fragmentation, hormogonia formation, and the development of new trichomes from heterocysts and akinetes.
Economic Importance of Cyanobacteria
- Serve as a protein-rich food source (e.g., Spirulina).
- Used as biofertilizers (e.g., Nostoc, Anabaena).
- Control mosquito larvae in ponds (e.g., Aulosira).
- Can contaminate drinking water reservoirs.
- Some species are toxic to animals.
Archaebacteria
Archaebacteria, also known as extremophiles, thrive in extreme environments. Their unique cell wall composition and complex lipid membranes enable them to withstand harsh conditions. They are categorized into methanogens, halophiles, and thermoacidophiles.