Cyanobacteria and Autotrophic Protists (Algae) Flashcards

Bio23: Organismal and Environmental Biology Lab 13: Cyanobacteria and Autotrophic Protists (Algae)

Objectives

• Learn about cyanobacteria and algae diversity.

• Observe and identify defining features of cyanobacteria and algae.

• Learn how key structures and features connect to life history strategies.

Introduction to Photosynthetic Organisms

• The lab focuses on photosynthetic bacteria, algae, plants, fungi, and lichens.

• Key aspects include evolutionary history, adaptations, and connections to ecology and life history.

• Life history is defined as how organisms allocate time and energy to maximize reproductive output, including habitat, energy/nutrient acquisition, and reproduction.

• The lab emphasizes connecting observed features and structures to life history.

• The lab provides a closer look at the diversity of autotrophic unicellular and multicellular organisms, specifically cyanobacteria and algae.

Cyanobacteria

Background

• Formerly known as "blue-green algae," cyanobacteria were reclassified as prokaryotes in the 1970s.

• Cyanobacteria represent a monophyletic group within bacteria.

• They are the only prokaryotes capable of oxygenic photosynthesis.

• Fossil records indicate their presence dating back at least 2.7 billion years.

• For approximately one billion years, they were the primary producers on Earth.

• Their photosynthesis led to the early increase in atmospheric oxygen, resulting in banded iron formations, red beds, and the evolution of aerobic respiration.

• Eukaryotes acquired oxygenic photosynthesis through endosymbiosis, incorporating cyanobacteria as chloroplasts.

• Cyanobacteria are still prevalent and vital in both aquatic and terrestrial environments.

• Some species can also fix atmospheric nitrogen (N2 to NH3 - ammonia or NH_4^+ - ammonium ion), making it available to other organisms.

• Both free-living and symbiotic cyanobacteria contribute to nitrogen fixation.

• Some nitrogen-fixing cyanobacteria possess specialized cells called heterocysts (or heterocytes) to facilitate this process.

• However, other cyanobacteria can fix nitrogen without specialized cells under certain conditions.

• Cyanobacteria can be unicellular, with some forming colonies held together by mucilage (polysaccharide substance).

• Filamentous forms exist, representing a type of multicellularity.

• Many species form symbiotic relationships with plants or fungi.

• Traditionally, cyanobacteria are classified into five taxonomic sections based on morphology.

• Sections I and II include unicellular species, while sections III to V contain filamentous taxa.

• Current phylogenetic studies indicate that many of these groups are not monophyletic.

• The lab uses the traditional section classification system for simplicity.

• It's crucial to remember that these sections are based on morphology and do not accurately represent evolutionary history.

Morphological Sections

• Section I: Unicellular, colonial cyanobacteria (e.g., Merismopedia, Eucapsis). Note the mucilage surrounding the Merismopedia cells.

• Sections III-V: Filamentous cyanobacteria, also called trichomes. Note the size and shape of the cells that comprise the trichomes. Look for dead cells with an 'empty' appearance. Each species can reproduce by fragmentation and the formation of hormogonia (short filaments released from the parent filament after the programmed death of adjacent cells).

• Section III: Filamentous with no specialized cells or branches (e.g., Oscillatoria, Spirulina). Note trichomes and, if visible, hormogonia, as well as the movement of Oscillatoria.

• Section IV: Filamentous with specialized cells but no branches (e.g., Nostoc). Note the individual cells and heterocysts. These specialized cells include heterocysts (heterocytes), which are used for nitrogen fixation. Compared to ordinary cells, heterocysts are often larger, roughly spherical or barrel-shaped, and appear relatively 'empty'. Akinetes (read more about akinetes in the handouts on the lab bench).

Autotrophic Protists (Algae)

Background

• "Algae" is a historical term for a diverse group of photosynthetic organisms, generally simpler in morphology than plants (bryophytes, pteridophytes, and seed plants).

• Algae range from unicellular to large, multicellular organisms known as "seaweeds."

• Algae demonstrate the evolutionary progression of multicellularity: unicellular → filamentous (1D growth) → planar/thalloid (2D growth) → 3D forms resembling plants.

• This evolutionary trend led to the emergence of the Kingdom Plantae from green algae.

• Traditionally, algae were classified based on plastid accessory pigments, resulting in color-based groupings (red, green, brown algae).

• Modern classifications use various characters, including cell wall components, reproductive structures, and food storage molecules.

• Algae are the primary producers in aquatic environments, making them ecologically significant.

Supergroup SAR

Stramenopiles

• Phaeophyta (brown algae): Macroscopic marine algae called seaweeds (e.g., Macrocystis, Sargassum, Leathesia, Analipus). Most are large and multicellular; only a few genera occur in freshwater. They posses chlorophyll, the carotenoid fucoxanthin, which impart a brown color; they share this pigment with diatoms and many dinoflagellates. Carbohydrates are stored as laminarin, similar to chrysolaminarin in diatoms.

• Key Features of Brown Algae: Holdfast (similar to roots), Stipe, Bladder (pneumatocyst), Blades, Pigments and starches.

• Diatoms: Unicellular or colonial organisms that are crucial components of phytoplankton in marine and freshwater systems (e.g., Navicula). Chloroplasts contain chlorophyll and fucoxanthin, giving them a golden-brown or brown-yellow color. They store carbohydrates as chrysolaminarin. Fossil evidence suggests they evolved during or before the Jurassic period. Fossil beds are known as "diatomaceous earth". Much of the world's oil deposits come from transformed organic remains of diatoms and other marine algae. Diatoms lack flagella and are non-motile. The cell wall, or frustule, consists of two halves made of hydrated silica dioxide, fitting together like a Petri dish. The frustules have ornate ornamentations used to distinguish species. Biotechnologists are exploring the use of diatoms for nanotechnology applications like nanoscale drug delivery.

• Observation: Types of pigments and starches in Navicula.

Alveolates

• Dinoflagellates: Unicellular protists (e.g., Peridinium, Ceratium, Synedra). They have an olive-brown color due to accessory pigments (peridinin or fucoxanthin) and elaborate shapes and ornamentation. Some marine species cause bioluminescence and red tides.

• Observation: Types of pigments in dinoflagellates.

Supergroup Archaeplastida

Rhodophyta (Red Algae)

• Largely marine and multicellular seaweeds (e.g., Gracilaria, Porphyra).

• Reddish color due to phycobilins (accessory pigments).

• Store carbohydrates as floridean starch.

• Cellulosic cell walls.

• Observation: Types of pigments and starches.

Viridiplantae (Green Algae and Plants)

• Within Archaeplastida, taxonomy and systematics gets messy.

• Two major groups of “green algae” – Chlorophyta and Charophyta – but these do not form a monophyletic clade.

• Chlorophyta is monophyletic and is the sister lineage to Charophyta, but nested deep within Charophyta are the land plants (Embryophyta).

• Although Charophytes are more closely related to land plants than they are to Chlorophytes, together all green algae share many similarities, and we will look at species from both lineages today in lab.

• Green algae consists contains organisms ranging from unicellular (Chlamydomonas, Chlorella) to colonial (Volvox) to multicellular (Ulva (sea-lettuce) and Chara (stonewort)).

• Green algae share the same chlorophyll pigment profile (chlorophyll a, b, beta-carotene and xanthophylls) as plants and have cellulosic cell walls.

• Chlorophyta: (e.g., Volvox, Chlamydomonas, Ulva, Scenedesmus).

• Charophyta: (e.g., Closterium, Zygnema, Spirogyra).

• Unicellular forms: (e.g., Chlamydomonas, Closterium).

• Filamentous unicellular forms: (e.g., Spirogyra, Zygnema).

• Colonial forms: (e.g., Volvox).

• Multicellular forms: (e.g., Ulva).

Here's a breakdown of the bolded terms from the provided lab notes, with more detailed explanations:

• Life history: This refers to how organisms allocate their time and energy throughout their lives to maximize reproductive success. It encompasses various factors such as habitat, strategies for acquiring energy and nutrients, and methods of reproduction. Understanding an organism's life history involves studying how it adapts to its environment and optimizes its survival and reproduction.

• Heterocysts (or heterocytes): These are specialized cells found in some nitrogen-fixing cyanobacteria. Their primary function is to provide an anaerobic (oxygen-free) environment where the enzyme nitrogenase can efficiently convert atmospheric nitrogen (N2) into ammonia (NH3) or ammonium ions ($$NH_4^+$). This process is crucial because nitrogenase is inhibited by oxygen. Heterocysts are structurally different from other cells, often appearing larger and more transparent.

• Section I: This is a morphological classification within cyanobacteria, specifically including unicellular and colonial forms. Examples include Merismopedia and Eucapsis. These cyanobacteria are characterized by their single-celled nature or their organization into colonies held together by mucilage, a polysaccharide substance.

• Sections III-V: These sections encompass filamentous cyanobacteria, also known as trichomes. These cyanobacteria are multicellular, forming thread-like structures composed of chains of cells. Reproduction occurs through fragmentation and the formation of hormogonia, which are short filaments released from the parent filament. Oscillatoria and Nostoc are examples.

• Phaeophyta (brown algae): Brown algae are a class of mostly marine, multicellular algae that include familiar seaweeds like Macrocystis and Sargassum. They contain chlorophyll and fucoxanthin, giving them a characteristic brown color. Brown algae have various specialized structures, including holdfasts for anchoring, stipes (stalks), bladders (pneumatocysts) for buoyancy, and blades for photosynthesis.

• Diatoms: These are unicellular or colonial stramenopiles that are important components of phytoplankton in both marine and freshwater ecosystems. They have cell walls (frustules) made of silica, which have intricate and ornate patterns. Diatoms contain chlorophyll and fucoxanthin, and store carbohydrates as chrysolaminarin, giving them a golden-brown color. They are non-motile and lack flagella.

• Dinoflagellates: Dinoflagellates are unicellular protists and are part of the Alveolates. They are characterized by their olive-brown color due to accessory pigments like peridinin and fucoxanthin. Some species are known for causing bioluminescence and red tides. Dinoflagellates have complex shapes and ornamentation.

• Rhodophyta (Red Algae): Red algae are a group of mostly marine, multicellular seaweeds. Their reddish color is due to the presence of phycobilins, which are accessory pigments that allow them to capture light in deeper waters. Examples include Gracilaria and Porphyra. They store carbohydrates as floridean starch and have cellulosic cell walls.

• Viridiplantae (Green Algae and Plants): Green algae, along with land plants, belong to the supergroup Archaeplastida. Green algae share similar chlorophyll pigments (chlorophyll a, b, beta-carotene, and xanthophylls) with plants, and their cell walls are made of cellulose, and can be unicellular, colonial, or multicellular.