Alberta West News: Primer on Microalgae/cyanobacteria

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Primer on Microalgae and Cyanobacteria

Fundamental Definitions

Microalgae are microscopic, photosynthetic organisms ranging from 2 to 200 micrometers in size that exist as unicellular species or in chains and groups. They are found in freshwater and marine aquatic systems, living both in the water column and sediments. Unlike terrestrial plants, microalgae lack roots, stems, or leaves and are specially adapted to environments dominated by viscous forces.evidencenetwork+1

Cyanobacteria, commonly called blue-green algae, are photosynthetic bacteria (prokaryotes) that are sometimes grouped with microalgae but are fundamentally different in cellular organization. They are distributed across freshwater, marine, and terrestrial habitats, existing either individually or in colonies as filaments or spheres. The term "blue-green algae" is somewhat misleading, as cyanobacteria can appear in various colors including red, brown, yellow, and pink depending on their pigment composition.greenwaterlab+2

Key Distinction: Prokaryotic vs. Eukaryotic

The most fundamental difference between these groups lies in cellular structure. Cyanobacteria are prokaryotic, lacking a membrane-bound nucleus, chloroplasts, mitochondria, and other organelles typical of eukaryotic cells. Instead, they contain photosynthetic membranes called thylakoids distributed throughout their cytoplasm and possess a thick, gelatinous cell wall composed primarily of murein (a peptidoglycan).byjus+2

Microalgae encompass both prokaryotic (cyanobacteria) and eukaryotic forms. Eukaryotic microalgae contain a nucleus, chloroplasts, mitochondria, endoplasmic reticulum, Golgi apparatus, and vacuoles—the membrane-bound organelles characteristic of more complex cells. Their cell walls typically consist of cellulose, which differs compositionally from bacterial cell walls.sciencedirect+1

Cellular Structure and Photosynthetic Apparatus

Cyanobacteria structure features a distinctive organization with an outer cellular layer, cytoplasm, and nuclear material. The cytoplasm is divided into two regions: the chromoplasm (colored outer region) containing thylakoids and storage granules, and the centroplasm (colorless inner region) containing DNA. Their cell wall consists of four layers, with the outer layer typically mucinous, forming a protective coating around cells or entire filaments.filter+1

Eukaryotic microalgae possess a more complex subcellular architecture with chloroplasts serving as dedicated photosynthetic organelles. These chloroplasts contain thylakoids where light reactions occur, and the cells can produce various pigments—chlorophyll a, chlorophyll b, carotenoids, and xanthophyll—depending on species and environmental conditions.taylorfrancis+1

Pigment composition differs significantly between groups. Cyanobacteria utilize unique pigments called phycobiliproteins (phycobilins), which include phycocyanin and phycoerythrin alongside chlorophyll-a and carotenoids. These phycobilins confer the characteristic blue-green coloration and allow efficient light harvesting across diverse wavelengths. Eukaryotic microalgae generally rely on chlorophylls and carotenoids as their primary light-harvesting pigments, though some groups (like diatoms) may contain additional pigments such as fucoxanthin.evidencenetwork+3

Major Classification Groups

Microalgae are classified into several major groups based on pigmentation, cellular structure, and evolutionary origin:wikipedia+2

Cyanobacteria (Cyanophyta) represent the prokaryotic group within microalgae and are responsible for much of the atmospheric oxygen production over geological time.

Chlorophyta (Green algae) contain chlorophylls a and b, store starch as reserve substances, and include both unicellular and multicellular eukaryotic species found in freshwater and marine habitats. Examples include Chlorella vulgaris and Scenedesmus.

Bacillariophyceae (Diatoms) are unicellular eukaryotic algae with silica-based cell walls and unique pigmentation including fucoxanthin, which gives them a golden-brown appearance.

Rhodophyta (Red algae) contain chlorophyll-a and red pigments; most are marine and found at depths exceeding 130 meters.

Chrysophyceae (Golden algae) are typically flagellated unicellular forms found in freshwater lakes and lagoons.

Phaeophyta (Brown algae) predominantly marine with chlorophyll-a and characteristic fucoxanthin pigmentation, typically inhabiting rocky coastal zones.

Photosynthesis and Metabolism

Both microalgae and cyanobacteria are photosynthetic organisms capable of converting light energy into chemical energy through oxygenic photosynthesis. This process releases oxygen as a byproduct and utilizes carbon dioxide, effectively making them primary producers in aquatic food webs.wikipedia+2

Microalgae demonstrate exceptional photosynthetic efficiency—approximately four times greater than terrestrial plants—and produce roughly half of the Earth's atmospheric oxygen while simultaneously utilizing the greenhouse gas CO₂. Their rapid growth rates (>1 day⁻¹ for many species) combined with high biomass productivity make them highly efficient at carbon fixation.pmc.ncbi.nlm.nih+2

Unlike most algae, cyanobacteria possess nitrogen-fixing capabilities through specialized cells called heterocysts (found in filamentous forms like Nostoc and Anabaena). These heterocysts create a microanaerobic environment necessary for the enzyme nitrogenase to function without oxygen inactivation. They convert atmospheric nitrogen (N₂) into ammonia (NH₃), nitrites, or nitrates that can be absorbed by the filament's vegetative cells and converted into proteins and nucleic acids. This nitrogen fixation occurs primarily during nighttime to prevent photosynthesis-generated oxygen from inhibiting the process.pubmed.ncbi.nlm.nih+4

Reproduction and Life Cycles

Microalgae reproduction occurs primarily through asexual means, with complex cell cycles crucial for growth and adaptation to changing conditions. Most species reproduce through binary fission or mitosis, completing their life cycles in hours to days—significantly faster than terrestrial plants. Some species can also reproduce sexually through zygote formation.pubmed.ncbi.nlm.nih+1

Cyanobacteria reproduction similarly occurs through binary fission but can also produce specialized reproductive structures: Akinetes are thick-walled, dormant cells that develop after storing food reserves and germinate under favorable conditions. Hormogonia are movable filaments exhibiting gliding motion that later develop into new filaments. Hormocysts are hormogonia with dense sheaths capable of producing new filaments through germination.byjus+1

Environmental Requirements and Growth Factors

Optimal growth conditions for microalgae vary by species but generally include:pmc.ncbi.nlm.nih+2

Light: 26-400 μmol photons m⁻² s⁻¹ for most species; only specialized species tolerate extreme light levels (3000-3500 μmol photons m⁻² s⁻¹). Light intensity directly affects photosynthesis rates logarithmically, with low light limiting growth and excessively high light inhibiting it. Photoperiod duration (hours of light:darkness) significantly influences biochemical composition.
Temperature: Optimal range typically 20-25°C for most species, though some adapt to extreme temperatures. Light saturation point decreases with declining temperature.
Nutrients: Microalgae require nitrogen, phosphorus, and sulfur, which they convert into carbohydrates, fats, and proteins. Nitrogen and phosphorus availability directly impacts growth rates, lipid accumulation, and production of valuable compounds like astaxanthin and omega-3 fatty acids. Nitrogen-limited conditions generally suppress growth but enhance lipid production.wikipedia
pH and salinity: Cyanobacteria show preference for high pH environments (alkaline conditions), while microalgae demonstrate broader tolerance across pH ranges and salinity levels.

Water characteristics: Growth accelerates in warm, slow-moving or still waters rich in nutrients—conditions conducive to both beneficial algal productivity and harmful blooms.cdc+1

Nutrient Storage and Biochemical Composition

A major compositional difference exists between microalgae and cyanobacteria: Microalgae (particularly green algae) store carbohydrates primarily as starch and cellulose, while cyanobacteria accumulate glycogen as their major storage polysaccharide. Both groups lack lignin, making their polysaccharides easier to break down than terrestrial plant biomass—advantageous for biofuel and biochemical extraction applications.sciencedirect

Microalgae accumulate diverse reserve substances including lipids, carbohydrates, and proteins within their cells, with concentrations varying by species and cultivation conditions. Many species can produce high-value compounds:evidencenetwork+1

Lipids and omega-3 fatty acids: Species like Nannochloropsis gaditana accumulate eicosapentaenoic acid (EPA) and other omega-3 polyunsaturated fatty acids, important for human nutrition and aquaculture feeds.cordis.europa
Astaxanthin: A potent lipid-soluble antioxidant produced by species including Haematococcus lacustris, often combined with fatty acids to form astaxanthin esters for food, feed, and pharmaceutical applications. Production is stimulated by high light intensity and nutrient stress conditions.pmc.ncbi.nlm.nih
Carotenoids and phycobiliproteins: Valuable pigments with nutritional and industrial applications.

Ecological Importance

Microalgae and cyanobacteria function as foundational components of aquatic ecosystems: They are primary contributors to oxygen production, serve as base-level food sources for zooplankton, insects, snails, and higher trophic levels, and form habitats for small aquatic animals. Many species—particularly nitrogen-fixing cyanobacteria—exert control over primary productivity and the export of organic carbon in aquatic systems.biologyonline+2

Cyanobacteria's historical role cannot be overstated. Over billions of years, early cyanobacteria continuously produced and released oxygen, converting Earth's anoxic prebiotic atmosphere into an oxidizing one with free gaseous oxygen, resulting in the Great Oxidation Event and fundamentally altering the composition of life forms on the planet.wikipedia

Harmful Algal Blooms and Cyanotoxins

Not all algal blooms are problematic; however, harmful algal blooms (HABs) occur when conditions promote rapid, excessive growth that can harm people, animals, or the environment. Blooms become harmful when they produce toxins, become too dense (reducing oxygen availability), or release harmful gases.epa+2

Factors promoting blooms include: Warm water temperatures, slow-moving or still conditions, high nutrient availability (particularly nitrogen and phosphorus from agricultural runoff or sewage), elevated light intensity, and high pH. Climate change and eutrophication from human activities have increased bloom frequency globally.publichealthontario+3

Cyanotoxins are poisonous substances produced by toxic cyanobacteria genera including Microcystis, Dolichospermum (formerly Anabaena), Planktothrix, Nostoc, and Microcoleus. The most commonly studied and problematic toxin is microcystin-LR, produced by Microcystis, which Health Canada identifies as the most important freshwater cyanotoxin.epa+1

Toxin release mechanisms: Most toxins are released into water during cyanobacterial cell death and lysis (rupture), though some species release toxins extracellularly without cell rupture. Once released, toxins persist in water bodies even after blooms visually disappear.publichealthontario+1

Health effects from exposure (through ingestion, skin contact, or inhalation) range from minimal—diarrhea, headaches, and skin irritation—to potentially life-threatening, including neurotoxicity, hepatotoxicity, and endotoxemia. Animals, particularly dogs, are more susceptible to fatal toxin exposures than humans. A notable example of chronic bloom problems is Lake Winnipeg, termed "Canada's sickest lake" and "the most threatened lake in the world" due to recurring eutrophication-driven blooms.waterportal

Applications and Biotechnological Potential

Biofuel production: Microalgae are considered viable feedstock for third and fourth-generation biofuels. They produce 20-50% oil content (dry biomass weight), generating more oil per acre than any terrestrial crop. Cultivation takes 7-14 days depending on conditions, vastly shorter than agricultural cycles. Advantages include non-competition with food crops for arable land, ability to grow in seawater and wastewater, and lower environmental footprints than terrestrial biofuel sources.tandfonline+1

Wastewater treatment: Microalgae thrive in nutrient-rich wastewater, simultaneously removing excess nitrogen and phosphorus (reducing eutrophication risks), assimilating heavy metals through biosorption and bioaccumulation, and purifying water quality. Species like Chlorella vulgaris can eliminate pollutants from textile wastewater to below legal discharge limits while maintaining productive growth and accumulating valuable pigments.pmc.ncbi.nlm.nih

Carbon sequestration: Microalgae sequester atmospheric CO₂ at rates 10-50 times greater than terrestrial plants without competing for agricultural land. For every kilogram of biomass produced, microalgae sequester approximately 1.3 kg of CO₂. Their rapid growth and high photosynthetic efficiency make them effective for carbon capture in photobioreactors using industrial flue gases and waste streams.pmc.ncbi.nlm.nih

Soil improvement and biofertilization: Functioning as biofertilizers and biostimulants, microalgae increase crop yields by 5-25%, reduce chemical nitrogen requirements by up to 50%, and enhance soil aggregation through extracellular polymeric substances (EPSs). Multi-strain microalgal consortia combining nitrogen-fixing cyanobacteria with plant growth regulators improve soil health in degraded environments.pmc.ncbi.nlm.nih

Food and nutrition: Market demand for microalgae was projected at USD 55.67 billion by 2031. Applications include incorporation into functional foods (soups, juices, biscuits, ice creams) as nutritional supplements, natural coloring agents, and sources of omega-3 fatty acids and astaxanthin for human and aquaculture nutrition. Natural astaxanthin in feed increases growth rates of aquatic organisms without negative health effects, offering an alternative to synthetic hormones and chemicals.pmc.ncbi.nlm.nih+2

Biorefinery integration: Sequential extraction of multiple bioproducts from microalgal biomass—including lipids, proteins, carbohydrates, pigments, and bioactive compounds—improves economic feasibility of commercial microalgae production.pmc.ncbi.nlm.nih+1

Current Challenges

While microalgal biotechnology shows remarkable promise, significant barriers to commercialization persist: high production costs, technical complexities in scaling outdoor cultivation systems, dynamic biofilm structures influenced by substrate type and environmental conditions, regulatory gaps, and economic competition with established fossil fuel and agricultural systems. Species selection remains critical, as algal performance varies substantially with pollutant types and environmental conditions.pmc.ncbi.nlm.nih

Recent breakthroughs in cultivation systems, biorefinery integration, and strain optimization indicate promising pathways forward for overcoming these limitations and realizing the full potential of microalgal biotechnology in addressing energy, environmental, and agricultural challenges.

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Primer on Microalgae/cyanobacteria