Microbial Life, Plant, and Fungal Diversity: Study Notes

Microbial Life: Prokaryotes and Protists

Introduction to Microbial Life

Microorganisms, including prokaryotes and protists, are essential components of Earth's biosphere and play critical roles in human health and ecological processes. The human body hosts trillions of microbial cells, which can influence susceptibility to diseases and various health conditions.

• Microbial communities can affect immune responses and are linked to diseases such as asthma, allergies, and digestive disorders.

• Disruption of these communities may contribute to complex conditions, including autism.

Prokaryotes: Diversity and Characteristics

Prokaryotes are unicellular organisms lacking a nucleus and membrane-bound organelles. They are classified into two domains: Bacteria and Archaea.

• Prokaryotic cells are generally smaller than eukaryotic cells.

• Their collective biomass exceeds that of all eukaryotes combined.

• Prokaryotes are found in nearly every environment on Earth and have significant ecological and medical impacts.

Prokaryotic Cell Shapes

• Cocci: Spherical cells

• Bacilli: Rod-shaped cells

• Spirilla: Short, rigid spiral cells

• Spirochetes: Long, flexible spiral cells

Cell Wall Structure and Gram Staining

• Most prokaryotes possess a cell wall, which can be classified by the Gram stain technique:

  • Gram-positive bacteria: Thick peptidoglycan layer, stain purple

  • Gram-negative bacteria: Thin peptidoglycan layer, outer membrane, stain pink

• Other features: Capsules (protection/adhesion), flagella (movement), fimbriae (attachment)

Adaptation and Nutritional Diversity

• Rapid reproduction and genetic variation enable prokaryotes to adapt quickly to environmental changes.

• Some form endospores to survive harsh conditions.

• Prokaryotes display diverse nutritional strategies:

  • Phototrophs: Use sunlight for energy

  • Chemotrophs: Obtain energy from chemicals

Biofilms and Environmental Roles

• Biofilms: Complex microbial communities attached to surfaces, often resistant to removal.

• Bioremediation: Use of prokaryotes to clean up pollutants in soil, water, and air.

Prokaryotic Evolution: Bacteria and Archaea

• Genetic studies reveal that Archaea are more closely related to Eukarya than to Bacteria.

• The three domains of life: Bacteria, Archaea, Eukarya.

Archaea: Extremophiles and Other Habitats

• Extreme halophiles: Thrive in high-salt environments

• Extreme thermophiles: Thrive in high-temperature environments

• Methanogens: Produce methane in anaerobic conditions

Bacterial Diversity

• Proteobacteria: Gram-negative, diverse metabolism (e.g., Thiomargarita namibiensis)

• Gram-positive bacteria: Includes antibiotic producers (e.g., Streptomyces)

• Cyanobacteria: Photosynthetic, oxygen-producing (e.g., Anabaena)

• Chlamydias: Intracellular parasites (e.g., Chlamydia trachomatis)

• Spirochetes: Spiral-shaped pathogens (e.g., Treponema pallidum)

Pathogenic Bacteria and Toxins

• Exotoxins: Secreted proteins causing disease (e.g., Staphylococcus aureus)

• Endotoxins: Released from Gram-negative bacteria upon cell death

• Bacterial toxins can be used as biological weapons (e.g., botulinum toxin from Clostridium botulinum)

Protists: Diversity and Classification

Protists are mostly unicellular eukaryotes found in aquatic or moist environments. They exhibit diverse nutritional modes:

• Autotrophic (algae): Photosynthetic

• Heterotrophic (protozoans): Ingest food

• Mixotrophic: Both photosynthetic and heterotrophic

Protist Supergroups

• SAR: Stramenopila (diatoms, brown algae, water molds), Alveolata (dinoflagellates, ciliates), Rhizaria (foraminiferans, radiolarians)

• Excavata: Includes Giardia, Trichomonas, Trypanosoma, Euglena

• Unikonta: Amoebozoans (amoebas, slime molds), fungi, and animals

• Archaeplastida: Red algae, green algae, and land plants

Evolution of Multicellularity

• Multicellularity evolved independently in several eukaryotic lineages, including brown algae, fungi, animals, and plants.

• Specialization of cells enabled increased complexity and diversity.

The Evolution of Plant and Fungal Diversity

Plant Evolution and Adaptations

Plants evolved from green algal ancestors and adapted to terrestrial life through a series of key innovations.

• Advantages of land: More sunlight, abundant CO2, initially fewer pathogens/herbivores

• Challenges: Water retention, structural support, reproduction without water, anchorage, resource acquisition

Major Events in Plant Evolution

• Origin of land plants

• Origin of vascular plants (with lignin-hardened tissues)

• Origin of seed plants (with pollen and seeds)

Plant Diversity

• Nonvascular plants (bryophytes): Mosses, hornworts, liverworts

• Seedless vascular plants: Lycophytes (club mosses), monilophytes (ferns and relatives)

• Seed plants: Gymnosperms (seeds in cones), angiosperms (seeds in ovaries/flowers)

Alternation of Generations

• Plant life cycles alternate between haploid gametophyte and diploid sporophyte generations.

Seedless Vascular Plants and Fossil Fuels

• Ancient seedless vascular plants formed vast coal forests during the Carboniferous period.

• Fossil fuels (coal, oil, natural gas) originated from these and marine organisms.

• Burning fossil fuels releases greenhouse gases, contributing to climate change.

Pollen and Seeds: Adaptations for Land

• Pollen grains transport sperm without water.

• Seeds protect and nourish the embryo, aiding dispersal and survival.

Angiosperm Reproduction: The Flower

• Flowers are reproductive structures housing male (stamens) and female (carpels) organs.

• Pollination and fertilization occur within flowers.

• Ovaries develop into fruits, which aid in seed dispersal.

Fruits and Seed Dispersal

• Fruits are ripened ovaries that protect seeds and facilitate dispersal by wind, animals, or other mechanisms.

Importance of Angiosperms

• Angiosperms provide most of the world's food, including grains, fruits, and spices.

Pollination and Angiosperm Evolution

• Flowers attract animal pollinators with color and scent.

• Pollinators are rewarded with nectar and pollen, facilitating cross-pollination and genetic diversity.

Plant Diversity and Food Security

• Loss of plant biodiversity threatens food security and the availability of valuable genes for crop improvement.

• Conservation of wild and local plant species is vital for future agriculture.

Diversity of Fungi

Fungi are heterotrophic eukaryotes that absorb nutrients after external digestion. They play essential ecological and economic roles.

• Fungal bodies consist of hyphae (threadlike filaments) forming a mycelium.

• Mycorrhizae: Symbiotic associations between fungi and plant roots, enhancing nutrient uptake.

Fungal Reproduction

• Fungi reproduce by spores, both sexually and asexually.

• Sexual reproduction involves fusion of hyphae, a heterokaryotic stage, nuclear fusion, and meiosis.

Fungal Classification

• Zygomycetes: Black bread mold

• Glomeromycetes: Form mycorrhizae with plants

• Ascomycetes: Sac fungi

• Basidiomycetes: Club fungi (mushrooms)

Ecological and Practical Roles of Fungi

• Decomposers: Break down organic matter, recycle nutrients

• Symbionts: Mycorrhizae, lichens (fungi + algae/cyanobacteria)

• Bioremediation: Decompose pollutants

• Food and biotechnology: Mushrooms, cheese, bread, alcohol, antibiotics, biofuels

Parasitic Fungi

• About 30% of fungi are parasites or pathogens of plants and animals.

• Examples: Corn smut (plants), ringworm, athlete's foot, yeast infections (humans)