Microbial and Plant Diversity: Eukaryotic Algae Phytoplankton

Introduction

• Eukaryotic algae

  • Definition: diverse group of photosynthetic organisms that share similar characteristics but do not reach the level of differentiation found in higher plants.

  • Importance in ecosystems and contributions to primary production and carbon fixation.

• Overview of the material:

  • Definition of eukaryotic algae

  • Evolution of eukaryotic algae

  • Characteristic features of algae

  • Main groups of algae

Definition of Algae

• The term "algae":

  • Abandoned as a strict taxonomic term but still in use among biologists.

  • Fritsch (1935) defines algae as:

  • "…unless purely artificial limits are drawn, the designation algae must include holophytic (photosynthetic via chlor. a) organisms (as well as their numerous colorless derivatives) that fail to reach the level of differentiation characteristic of archegoniate plants (e.g., mosses, liverworts, and ferns)."

Characteristics of Algae

• Diversity:

  • Range from unicellular, colonial to multicellular forms.

  • Many classes encompass both uni- and multicellular representatives.

• Habitat:

  • Found in various aquatic environments: marine, brackish, freshwater, hot springs, and terrestrial soils, snow, rocks, and desert soils.

• Growth Rates:

  • Some of the fastest growth rates among living organisms.

• Carbon Fixation:

  • Algae perform some of the highest levels of carbon fixation, critical for mitigating climate change.

• Ecological Role:

  • Positioned at the base of aquatic food chains, serving as primary producers.

Evolution of Photosynthesis

• Origin: Photosynthesis first evolved in bacteria.

• Cyanobacteria:

  • Also known as blue-green algae.

  • Classified as oxygenic photosynthesizers, meaning they produce oxygen.

• Other groups do not include oxygenic attributes.

Endosymbiosis

• Definition: Ecological interaction where one organism lives inside another.

• Key Events:

  • Primary Endosymbiosis:

  • Involved a cyanobacterium and a protist leading to the later development of chloroplasts in eukaryotic cells.

  • Secondary and Tertiary Endosymbiotic Events: Further integrations involving photosynthetic organisms.

• Diagram Representation (Rothschild, 2004):

  • Chloroplast s derived from a cyanobacterial origin with dual membranes.

  • Sequence illustrated involving different algal and host cell interactions.

Secondary Endosymbiosis

• Characteristics:

  • Green and red algae underwent secondary endosymbiotic events:

  • Secondary plastids consist of three membranes; the nucleus and mitochondria degenerate.

• Plastids:

  • Structures formed during this process include the inner and outer membranes of the cyanobacterial origin and additional membranes from the host cell (phagosomal).

Tertiary Endosymbiosis

• Definition:

  • A subsequent layer of endosymbiosis in which a dinoflagellate (tertiary host) engulfs another photosynthetic eukaryote (secondary host).

  • Diagram illustrating stages of complexity and the evolution of membrane structures.

Serial Endosymbiosis Examples

• Dinoflagellates:

  • Instances of serial secondary endosymbiosis with green algal cells (e.g., Lepidodinium chlorophorum).

• Tertiary Examples:

  • Various species with tertiary endosymbiotic events exhibiting advanced plastic structures (e.g., Durinskia agilis with diatoms).

Phytoplankton Characteristics

• Cyanobacteria:

  • Possess chlorophyll a and phycobiliproteins.

  • Distinct features:

  • Circular DNA, thylakoids arranged singularly.

• Phytoplankton Cell Wall:

  • Prokaryotic structures possess a double membrane with a peptidoglycan layer retained only in Glaucophytes.

  • In other groups, this layer has been lost.

• Photosynthetic Pigments:

  • Essential to understanding algal physiology and classification.

  • Variants include chlorophyll a, b, c (c1 & c2), and d, alongside carotenoids and phycobiliproteins.

Main Types of Algae

• Glaucophyta:

  • Considered early evolutionary algae; retain peptidoglycan layer; produce cyanelles.

• Chlorophyta:

  • Green algae with cellulose cell walls; often ancestors to land plants.

• Rhodophyta:

  • Red algae are key players in marine environments; involve diverse lineages.

• Dinophyta:

  • Recognized for harmful algal blooms; exhibit mixotrophic capabilities; possess unique organelles.

• Bacillariophyceae (Diatoms):

  • Notable for silica cell walls; significant CO2 fixers.

• Prymnesiophyceae (Haptophytes):

  • Resilient to environmental changes; contributes to primary productivity.

• Cryptophyceae:

  • Capable of photosynthesis in low-light conditions; symbiotic interactions.

• Other Groups:

  • Explore Apicomplexa and Heterokontophyta that also contribute significantly to ecology.

Quick Recap

• Covered themes: eukaryotic algae definitions, evolutionary history, characteristic features, and the primary and secondary endosymbiotic events that contribute to phytoplankton diversity.