Algae & Bacteria

Tree of Life

  • Major Groups in the Tree:
      - Eukarya includes:
        - Paramecium
        - Giardia
        - Synechococcus (Cyanobacterium)
        - Chloroplasts & Mitochondria
        - Escherichia and Bacillus (Bacteria)
        - Animals, Plants, Green Algae, Euglena, Some Thermophilic Isolates

Viruses

  • Role of Viruses:
      - Viruses are significant agents of disease for both aquatic organisms such as fish, amphibians, and various invertebrates, as well as for humans.
      - Can infect a variety of hosts, leading to both acute and chronic infections that impact health and populations.
      - Recent research has highlighted the concept of the 'viral ecological role' in aquatic systems:
        - Suggests that viruses might serve as regulators of productivity by controlling microbial community dynamics.
        - By lysing cells, they release nutrients back into the environment, influencing nutrient cycling and ecosystem dynamics.

  • Viral Shunt:
      - A crucial ecological mechanism where viruses facilitate the conversion of particulate organic matter into dissolved organic matter (DOM).
      - Prevents the upward transfer of organic material to higher trophic levels in food webs.
      - Vital in maintaining the health of microbial loop systems.
      - By recycling organic material, the viral shunt enhances the growth and productivity of microorganisms, such as bacteria.
      - Studies suggest this process can be as efficient as other organic matter recycling pathways during high viral activity, underlining the intersecting roles of viruses in nutrient dynamics.

Archaea

  • Characteristics:
      - Single-celled organisms lacking a nucleus or organelles.
      - Reproduce asexually.
      - Typically reside in extreme environments.
      - Metabolically diverse: can be photoautotrophic, chemotrophic, or heterotrophic.
      - Includes methanogens in wetland environments.

Methanogenesis in Archaea

  • Hydrogenotrophic Methanogenesis:
      - Reaction occurring in anoxic habitats such as swamps, marshes, hot springs, and during permafrost thaw.

  • Acetoclastic Methanogenesis:
      - Reaction occurring in anoxic sediments, especially in cold settings at the bottoms of temperate lakes and alpine wetlands.

Bacteria

  • Characteristics:
      - Single-celled, no nucleus or organelles.
      - Represent the greatest biomass on Earth; vital for regulating energy flow in aquatic ecosystems.
      - Extremely metabolically diverse, showing all forms of metabolism.
      - Some bacterial species are pathogenic.

  • Bacteria and the Sulfur Cycle:
      - Sulfur Reducing Bacteria: - Converts sulfate to hydrogen sulfide under anoxic conditions.
      - Sulfur Oxidizing Bacteria: - Converts hydrogen sulfide back to sulfur or sulfate.
      - Chemosynthetic processes: - Utilize chemical energy to produce organic matter.
      - Photosynthetic Sulfur Bacteria: - Use light and hydrogen sulfide for photosynthesis.

Bacteria and the Microbial Loop

  • Key players that facilitate the cycling of nutrients in the food web, including:
      - Algae
      - Heterotrophic flagellates
      - Ciliates
      - Zooplankton
      - Bacteria

  • Fish are at the top of this interconnected food chain diagram, indicating the trophic relationships.

Cyanobacteria

  • Characteristics:
      - Single-celled, may be solitary or form colonies/filaments.
      - Major oxygen producers through photosynthesis; considered the earliest life forms thriving in diverse habitats.
      - Competitive advantages in eutrophic waters due to gas vesicles providing buoyancy.
      - Contains phycobilin pigments that absorb light in the green spectrum, unavailable for other algae.
      - Often includes stringy and potentially toxic forms such as Aphanizomenon (Fannie), Microcystis (Mike), Anabaena (Annie).

Cyanobacterial Blooms

  • A global issue exacerbated by nutrient enrichment and warming conditions, leading to increased bloom production.

  • Toxic blooms such as Microcystin are human neurotoxins and contribute to water quality concerns, causing a global water management crisis.

Cultural Eutrophication

  • A locally-sourced global issue with examples including:
      - Lake Erie
      - Lake Okeechobee
      - Lake Taihu in China.

Nitrogen Fixation in Cyanobacteria

  • Resting Cells: Known as akinetes.

  • N-Fixation Sites: Specialized cells known as heterocytes, where nitrogen fixation occurs, necessitating thick cell walls and an anaerobic environment.

Cyanobacterial Mats

  • Examples include Scytonema and Schizothrix.

  • Found in oligotrophic habitats; they exhibit resilience to high light and drying conditions.

  • Contribute to the formation of marl (calcium carbonate) soils, contributing to limestone formations.

  • Specific habitats include marine stromatolites and Everglades mats.

Structure of Cyanobacterial Mats

  • Within these mats, calcium carbonate crystals and cyanobacterium are found in crystalline sheaths alongside diatoms and bacteria.

Protoctista

  • A diverse kingdom that includes:
      - Single and multicellular organisms like algae and heterotrophic protists.
      - Key drivers of primary production and nutrient cycling in aquatic ecosystems.

Major Algal Groups

  • Rhodophyceae (Red Algae):
      - Contain chlorophyll a and phycoerythrins; utilize blue-green light.
      - Primarily found in streams rather than freshwater habitats.

  • Chrysophyceae (Golden Algae):
      - Composed of chlorophyll a, c, and carotenoids, with chrysolaminarin as a cell wall.
      - Predominantly limp plankton in freshwater.

  • Bacillariophyceae (Diatoms):
      - Contain chlorophyll a, c, and carotenoids with silica cell walls (frustules).
      - Crucial players in plankton and benthos, responsible for approximately one-third of Earth's oxygen production.
      - Types include Pennate and Centric diatoms.

  • Uses for Diatoms:
      - Composed of diatomite, applied as abrasives in shoe polish and historically in toothpaste, also used in aquarium filters and beverage filtration.
      - Serve as indicators of environmental change due to their presence, short generation times, sensitivity to environmental gradients, preservation in sediment, and identifiable characteristics.

Diatom-Based Assessment of Water Quality

  • Serve as bioindicators due to several characteristics:
      1. Ubiquitous Presence: Found in nearly every aquatic environment.
      2. Short Generation Time: Rapid reproduction allows them to reflect recent environmental changes.
      3. Environmental Gradients: Varied responses to temperature, salinity, and nutrient concentrations aid in understanding local ecology.
      4. Readily Preserved: Silica frustules are durable, providing a geological record of past environments.
      5. Identifiable Characteristics: Morphological features allow for precise identification at the species level, aiding in biostratigraphy and paleoecology.

Indicators of Past Environmental Conditions by Diatoms

  • Diatom analysis can identify impacts from acid rain, nutrient loading, and climate change dynamics.

Dinophyceae (Dinoflagellates)

  • Characteristics:
      - Unicellular, free-swimming organisms with two flagella.
      - Cellulose cell wall provides protective armor; primarily planktonic.
      - Certain species contribute to harmful algal blooms (HAB) such as Pfiesteria piscicida and Karenia brevis (notable for red tides).

Euglenophyceae

  • Contains chlorophyll a and b with a protein cell wall.

  • Found typically in eutrophic waters, associated with sediments.

  • Capable of phagotrophy and motility; some possess a flagellum and a red photoreceptive spot.

Cryptophytes

  • Exhibit chlorophyll a and c; lack a cell wall but possess two flagella; capable of mixotrophy.

Xanthophytes

  • Yellow-green algae featuring chlorophyll a, c, carotenoids; characterized by two flagella and colonial forms like Cryptomonas.

Chlorophyceae (Green Algae)

  • Possess chlorophyll a and b and a cellulose (naked or calcified) cell wall.

  • Highly adapted to various habitats, showcasing a high species diversity (up to 20,000 species).

  • Morphologically diverse, including unicellular, colonial, and filamentous forms.

Charophyceae (Stoneworts)

  • Inhabit benthic environments in slow-flowing waters, can form calcareous mats with visible macroscopic structures.

Protozoa

  • Defined as unicellular heterotrophs capable of ingesting or absorbing organic carbon.

  • Important as parasites and resilient to environmental extremes; play essential roles in microbial loops within freshwater ecosystems.

  • Example: Naegleria fowleri, known as a "brain-eating amoeba", transitioning between trophozoite and flagellated forms, can lead to primary amoebic meningoencephalitis (PAM).

Community Assembly and Species Distribution

  • Each protist group contributes significantly to biodiversity and regulates biogeochemical cycles.

  • Different traits across groups provide multiple niches and influence distribution.

  • Community assembly driven by environmental variations allows coexistence across similar niches.

  • Seasonal succession can be anticipated based on relationships between traits and environmental conditions.

Phytoplankton Communities and Species Diversity

  • Addresses Hutchinson’s Paradox of the Plankton - why many species coexist despite similar niche requirements:
      - Influencing Factors:
        - Non-uniform physical conditions.
        - Size-selective grazing by zooplankton.
        - Diurnal migration of species.
        - Common symbiotic relationships and facilitative interactions.

Factors of Nutrient Limitation

  • Nitrogen (N) and Phosphorus (P) Limitation:
      - Interactions can result in:
        - Single limitation (N or P only).
        - Co-limitation (both nutrients).
        - Additional complexity from light limitations.

Mechanisms for Photic Zone Survival

  • Density regulation achieved through gas and sap vacuoles.

  • Particle size influences nutrient acquisition due to sinking dynamics.

  • Structural adaptations enhance surface area to volume ratios for prolonged survival in the water column.

  • Mucilage production creates gelatinous sheaths to reduce sinking rates.

Phytoplankton Defense Strategies Against Grazing

  • Strategies include:
      - Chemical deterrents (toxicity).
      - Structural defenses (thick cell walls, mucous secretion).
      - Digestion resistance.
      - Behavioral adaptations (rapid growth).
      - Physical structures (colonies, spines, filamentous forms) facilitating avoidance.

Mutualisms in Phytoplankton Communities

  • Metabolically Cohesive Consortia (MeCoCo):
      - Involves complex interactions between phytoplankton and bacteria regarding nutrient competition (inorganic nutrients, macronutrients, vitamins like B12).

Vertical Distribution and Chlorophyll Dynamics

  • Observations include:
      - Graphs of chlorophyll-a concentration and dissolved oxygen levels across depth variations.
      - Studying how environmental factors influence biodiversity and community composition.

Seasonal Succession Models for Phytoplankton

  • Trait-based Theory of Seasonal Succession:
      - Explains how phytoplankton traits determine seasonal dynamics and succession in aquatic ecosystems:
        - Spring Phase: Temperature rises and light increases, leading to diatom blooms due to adaptations for cold and nutrient-rich conditions.
        - Clear Water Phase: Following diatom bloom, zooplankton consume phytoplankton, increasing water clarity and allowing new species dynamics.
        - Summer Phase: Warmer temperatures and lower nutrients favor cyanobacteria, which thrive under calm, stratified waters with lower N:P ratios.
        - Fall Phase: Cooling temperatures and renewed mixing create nutrient conditions favorable for another diatom bloom.

Overall Concept

  • Phytoplankton communities are shaped by:
      - Environmental conditions.
      - Species traits.
      - Biological interactions.
      - Temporal and spatial variability.