Microorganisms in the Ecosystem

Microorganisms in the Ecosystem

Overview of Microorganisms

• Prokaryotic Microorganisms (Unicellular)
  • a. Bacteria
  • b. Archaea
• Eukaryotic Microorganisms (Unicellular and Multicellular)
  • a. Fungi
  • b. Protists:
  • I. Algae
  • II. Protozoa
  • III. Slime Molds

Roles of Microorganisms in the Environment

• Decomposition of Organic Substances
• Agents of Nutrient Cycling: Carbon (C), Nitrogen (N), Sulfur (S), Phosphorus (P), etc.
• Fundamental Roles in Soil Aggregation
• Beneficial for Plant Growth
• Photosynthesis: Fix carbon
• Pathogenic Roles: Cause disease

Eukaryotic Microorganisms: Fungi

• Fungi Density: Approximately 100 Thousand to 1 Million cells per gram of typical fertile soil.
• Characteristics:
  • Heterotrophic (cannot produce its own food)
  • Aerobic
• Nutritional Methods:
  • Secrete enzymes into food and absorb digested materials through cell walls
  • Most are saprophytic (absorb organic materials from dead organisms), termed “nature’s recycler”
  • Many are microscopic

Structure of Fungi

• Hyphae: Filaments that collectively form mycelium
• Cell Walls: Contain chitin (also found in insect and crustacean exoskeletons)
• Reproduction:
  • Asexually (producing genetically identical offspring)
  • Sexually

Impact of Fungi

• Plant Pathogens: Majority are fungi, which can be harmful
• Beneficial Associations:
  • Mycorrhiza (beneficial associations with plant roots)
• Decomposers:
  • Dominant in soil, excellent at degrading organic residues
  • Minimally involved in the transformation of inorganic compounds

Structure of Fungal Cell Wall

• Components:
  • Mannoproteins
  • B-1,6-glucan
  • B-1,3-glucan {
  • Chitin
  • Phospholipid bilayer of the cell membrane
• Synthesis Enzymes:
  • Chitin synthase
  • B-1,3-glucan synthase
  • UDP-GlcNAc
  • UDP-Glc

Examples of Fungi and Their Environmental Roles

• Molds:
  • Rhizopus spp.: Found in spoiled food, soil, and crops - role in degradation, causes plant diseases (e.g., rice seedling blight)
  • Penicillium spp.: Found in spoiled food, soil - role in degradation, antibiotic (penicillin) production
• Mushrooms:
  • Polyporus squamosus: Found on dead trees and plant material - role in decomposition
• Pathogenic Fungi:
  • Cryptococcus neoformans: Soil and airborne, role in degradation, causes lung infections and affects the central nervous system in humans
• Yeasts:
  • Saccharomyces cerevisiae: Found in fruits, soils, and aquatic environments - role in fermentation and degradation
  • Candida albicans: Normal microbiota of animals, causes candidiasis (yeast infections) of the skin and mucous membranes

Mycorrhizal Fungi

• Fungi forming symbiotic relationships with plants
• Fungi ‘infect’ plant roots and act as an extension of the root system
• Increased Element Uptake: Increases uptake of phosphorus (P) and trace elements
• Plant Benefits: The plant provides the fungus with substrate (sugars)
• Presence: Ecto- and Endo-mycorrhizal fungi are present in 92% of all studied plant families

Protozoa: Animal-like Unicellular Organisms

• Characteristics:
  • All are unicellular and animal-like cells
  • Nutrition primarily through ingestion of other organisms (e.g., bacteria) or dead organic material
  • Some are parasitic and must live in or on a host (such as intestines or bloodstream of animals) to obtain a constant food supply

Modes of Locomotion of Protozoa

• Pseudopods: Move by pseudopodia (e.g. Amoeba)
• Flagellates: Move using flagella (e.g. Giardia)
• Sporozoans: Generally sessile with no movement (e.g. Plasmodium)
• Ciliates: Move using cilia (e.g. Paramecium)

Roles of Protozoa in the Environment

• Important in controlling bacterial populations and nutrient cycling, especially within the rhizosphere
• Considered zooplankton: A group of small animal organisms that float or drift in fresh or salt water, serving as food for larger aquatic animals
• Metabolism: Primarily chemoheterotrophic

Pathogenic Protozoa

• Examples of Human Pathogens:
  • Giardia and Cryptosporidium cause gastroenteritis
  • Naegleria fowleri and Balamuthia mandrillaris lead to brain encephalitis

Algae: Photosynthetic Microbes

• Characteristics Include:
  • Aerobic, photosynthetic, can be unicellular or multicellular, filamentous, and colonial
  • Utilize sunlight for energy and obtain carbon from CO2 in the air
  • Engage in oxygenic photosynthesis, major contributors to producing the planet’s oxygen
  • Serve as a foundation for the aquatic food chain
  • Some multicellular algae resemble plants

Classification of Algae

• Based on pigmentation
• Major photosynthetic pigment: Chlorophyll-a
• Reproduction: Both sexual and asexual reproduction noted
• Potentially hazardous: Can cause ‘blooms’ from nutrient overload, and some produce toxins harmful to human health
• Cell Wall Composition: Main component is cellulose

Structure of Eukaryotic Cells

Overview

• Features membrane-delimited nuclei
• Contains membrane-bound organelles performing specific functions
• More complex than prokaryotic cells and generally larger

Cytoplasmic Matrix and Cytoskeleton

• Cytoplasmic Matrix: Provides the complex environment needed for cellular activities
• Composed of liquid (cytosol) and various organelles
• Cytoskeleton:
  • Vast network of interconnected filaments within the cytoplasmic matrix
  • Includes microfilaments (actin), microtubules, intermediate filaments, and motor proteins
  • Plays a role in cell shape and movement

Mitochondrial Structure

• Outer Membrane and Inner Membrane: Highly folded to form cristae, the matrix contains ribosomes, mitochondrial DNA, and various granules
• Enzymatic Functionality: Site for the tricarboxylic acid cycle and ATP generation through electron transport and oxidative phosphorylation

Chloroplast Structure

• Chloroplast Envelope: Double membrane structure, contains stroma and thylakoids
• Thylakoids: Stacks (grana) trap light energy to generate ATP, NADPH, and oxygen during photosynthesis

Nucleus and Cell Division

• Nucleus: A membrane-bound structure housing genetic material
• Nuclear Structure: Composed of chromatin (dense fibrous material) condensing into chromosomes during cell division
• Nuclear Envelope: Double membrane with nuclear pores facilitating transportation in and out of the nucleus

Mitosis vs. Meiosis

• Mitosis: Involves a single component of the cell cycle that distributes DNA equally to two new nuclei
• Meiosis: A complex two-stage process resulting in daughter cells with half the number of chromosomes, transitioning from diploid to haploid

External Cell Coverings

• Includes structures like the cell wall and pellicle
• Cell Wall Composition: Varies (e.g., algae have cellulose and pectin, fungi have chitin and glucan)
• Pellicle: Provides a characteristic shape to protozoa; generally not as rigid as a cell wall

Cilia and Flagella

• Cilia: 5-20 μm long, beat in two phases
• Flagella: 100-200 μm long, move in an undulating fashion
• Structure: Composed of membrane-bound cylinders demonstrating a 9 + 2 arrangement of microtubules

Comparison of Cellular Types