KJ

Algae, Diatoms, Agar, and Protozoa: Comprehensive Study Notes

Algae and Phylogeny

  • Algae are related to cyanobacteria; modern terrestrial plants are related to algae. Algae and plants both have cellulose in their cell walls.
  • In short: algae, cyanobacteria, and plants are interconnected in phylogeny; cellulose as a shared feature links algae to plants.

Why algae are important and practical aspects

  • Algae have many uses for people (industry, food, medicine, etc.).
  • They are difficult to grow in the lab: lab culture conditions for algae are not typically compatible with standard bacterial culture conditions. This makes algae less frequently studied in some microbiology labs.
  • From a clinical microbiology standpoint: algae do not cause infections in humans; they rely on sunlight to produce their own food (photosynthesis). Therefore, they are not pathogens in the traditional sense.
  • If algae were to cause problems in an organism, it would be on surface exposures (sunlight-exposed areas) rather than inside the body where there’s no light.
  • Historically rare cases exist of algae growing on humans in marine environments, but these are extremely uncommon; more important allergic and irritant effects are discussed in other contexts.

Agar and seaweed-derived polysaccharides

  • Agar is a polysaccharide derived from red seaweed; used to solidify microbiological media (petri dishes, solid tubes).
  • Dissolution and solidification properties:
    • To disperse agar in liquid, heat to about 90^{\circ}C (boiling) so the agar dissolves.
    • When cooled to about 40^{\circ}C, it solidifies and remains solid until boiled again.
    • Most bacteria cannot metabolize agar, so it remains stable as a solid medium.
  • History and practical uses:
    • Gelatin (animal product) was used previously, but many organisms hydrolyze gelatin back to liquid; agar is more stable.
    • Agar is also used in foods (e.g., jellies) and is clearer than gelatin.
    • Agar’s firmness is often described as resembling Jell-O but firmer.
  • Seaweed-derived extracts used as thickeners:
    • Carrageenan and alginate are common seaweed-derived thickeners used in foods and other industries; alginates are used in medicine.
    • Alginate powders are resistant to breakdown by most organisms; agar is largely indigestible by most organisms.
  • Economic and historical notes:
    • There was a period in the mid-1980s with a significant price spike for agar due to red seaweed shortages, reaching around 500\,per\,lb after previously being around 100\,per\,lb.
    • Substitutes did not prove to be of comparable quality.
  • Industry and practical implications:
    • Thickeners from algae are important in cosmetics (e.g., hand lotions), where texture and slip matter for user experience; this involves some chemistry in algae-derived products.

Algae in food and nutrition

  • Algae are widely consumed as food: seaweeds (e.g., nori) and seaweed products (e.g., seaweed salads, seaweed chips).
  • Spirulina:
    • Sold as a powder and marketed as a “superfood” because it contains all essential amino acids and vitamins.
    • Spirulina is technically a cyanobacterium, not a true alga.
    • Some people dislike the smell but it is effective for others.

Diatoms and diatomaceous earth (DE)

  • Diatoms have cellulose cell walls reinforced with silica (silicaceous frustules); silica remains after death, forming diatomaceous earth (DE).
  • Diatomaceous earth is a very fine, abrasive white powder (looks like talcum powder).
  • Uses of DE:
    • Abrasive in car polishes and toothpaste.
    • Filtering agent in water treatment and swimming pools; used to filter particulates including algae.
    • In gardening and pest control: food-grade DE acts as a physical irritant that damages insect exoskeletons, reducing pest populations; considered non-toxic to humans.
  • Mining and material science:
    • Diatom beds are mined (e.g., in California) for DE production.

Algae in the environment and global oxygen production

  • Algae and cyanobacteria are major producers of atmospheric oxygen: about 70\% of global O2 comes from algae/cyanobacteria; terrestrial plants contribute roughly 30\%.
  • Atmospheric oxygen today is about 21\%, whereas in the time of the dinosaurs it was around 15-16\%. A drop to that level would be lethal to humans.
  • Algae, being aquatic, significantly influence water chemistry and ecosystem dynamics.

Algal blooms and ecological impacts

  • Algae thrive where nutrients are abundant; nitrogen and phosphorus are key limiting inputs for growth.
  • Nutrient inputs and proliferation:
    • Nitrogen and phosphorus enter aquatic systems via runoff and wastewater outputs, especially from hard surfaces (concrete, asphalt) and old septic systems.
    • Agricultural runoff (e.g., chicken farms) can dramatically increase nutrient loads in nearby waters (e.g., Chesapeake Bay area).
  • Eutrophication: excessive algal growth on the water surface can occur when nutrients are abundant; this can lead to light limitation for benthic (bottom-dwelling) organisms and subsequent die-off and decomposition.
  • Decomposition and oxygen depletion:
    • When algae die, bacteria and protozoa decompose the organic matter, consuming oxygen (aerobic respiration) and causing hypoxic or anoxic conditions, which can result in fish kills.
  • Algal blooms can also produce toxins that affect wildlife and humans; blooms may be visible from space (algal blooms can be large enough to be seen from satellites).
  • Toxin-producing groups and associated diseases:
    • Red tide: often caused by dinoflagellates; can tint the water red and produce toxins concentrating in shellfish, leading to shellfish poisoning (amnesic and paralytic types).
    • Amnesic shellfish poisoning (ASP) and Paralytic shellfish poisoning (PSP) can occur when shellfish filter toxins from algae.
    • The coastal East Coast is known for red tide events; NOAA and other agencies monitor these events and issue harvest advisories.
    • West Coast issues are often linked to diatoms or other dinoflagellates with toxins.
  • Toxin resistance and cooking:
    • Toxins are somewhat resistant to heating; cooking shellfish may not reliably remove toxins, so avoidance may be necessary in affected areas.

Algae as a potential biofuel source

  • Some algae accumulate high lipid content (up to about 50\% of dry weight in some species).
  • Growing algae as a biofuel feedstock can be done in small, low-cost setups (e.g., plastic bags, simple tanks, or even kitty pools), enabling potential rooftop cultivation.
  • The process concept:
    • Grow algae to accumulate lipids; extract oil for biodiesel; remaining biomass can be used as animal feed.
  • Industry and challenges:
    • Major energy and chemical companies (e.g., Exxon, Volvo) are involved in algal biofuel research and development.
    • Economic and technical challenges remain; scaling, cost, and lifecycle efficiency are critical factors.

Protozoa: Overview and importance

  • Protozoa belong to the kingdom Protista and are predominantly unicellular, non-multicellular animals (not photosynthetic) with no cell walls; some possess shells (e.g., formanifera).
  • They are diverse and numerous; many are heterotrophs and play a major role as decomposers and as part of aquatic zooplankton.
  • Habitats: fresh water, salt water, damp soils; some can inhabit the human body (intestinal protozoa) or other hosts.
  • Protozoa are typically classified by motility into four groups; most protozoa are free-living, with some parasitic species.
  • Important clinical relevance: several intestinal protozoa can infect humans; others can cause severe disease (e.g., amoebic meningitis) but many protozoa are tropical or travel-associated.
  • Resting forms: many intestinal protozoa form cysts to survive harsh environmental conditions; trophozoites are the active feeding forms.
  • Polymorphism: some protozoa are polymorphic, existing in multiple forms (trophozoite and cyst are common examples).

Protozoa resting forms and lifecycle concepts

  • Trophozoite: the active, feeding form in favorable conditions.
  • Cyst: a resting, often nonmetabolic or low-metabolic form that can survive harsh conditions (desiccation, chemicals, nutrient scarcity). Cysts enable transmission and persistence in the environment.
  • Polymorphic organisms: capable of forming multiple shapes or life stages.

Apicomplexa (Sporozoa) – non-motile intracellular parasites

  • Key feature: no motility in mature forms; complex life cycles often requiring more than one host.
  • Major pathogen example: Plasmodium spp. cause malaria; malaria remains a significant global health issue due to complex lifecycles and transmission.
  • Life cycle and transmission:
    • Requires an intermediate host (often a mosquito of the Anopheles genus) for sexual cycle stages and transmission to humans.
    • In the United States, malaria is not endemic primarily because the local mosquito species (e.g., Aedes, Culex) are not competent vectors for human malaria; most US cases are travel-associated.
  • Other apicomplexans and related pathogens discussed:
    • Toxoplasma gondii: common in Maryland; cats are the main reservoir; pregnant women can face fetal risk; TORCH panel tests assess fetal risk during pregnancy.
    • Cryptosporidium: cysts are highly resistant to chlorination; a major waterborne disease concern; implicated in 1990s outbreaks; particularly dangerous for immunocompromised individuals (e.g., advanced HIV).
  • Cryptosporidium in water treatment:
    • Chlorination alone may not be sufficient to kill cysts; filtration and other water treatments are important; crypto is a target in swimming pool safety protocols.

Mastigophora (Flagellates)

  • Move using one or more flagella; fast swimming cells are often observed in pond water samples.
  • Notable examples and diseases:
    • Giardia lamblia: causes giardiasis (“Giardia diarrhea”); commonly associated with contaminated water; flagellated parasite.
    • Trypanosoma spp. (e.g., T. gambiense): causative agents of African sleeping sickness; significant pathogenic hemoparasites.
    • Leishmania spp.: cause cutaneous and visceral leishmaniasis; transmitted by sandflies (phlebotomine vectors).
    • Trypanosoma cruzi: agent of Chagas disease; transmitted by kissing bugs (Triatominae); a concern for potential spread northward from Central/South America.
    • Trichomonas vaginalis: an STI (the “trich”);
  • Other highlights:
    • Blood parasites like trypanosomes and Leishmania have complex life cycles and vector-borne transmission.
    • Some flagellates can be human parasites with significant disease burden in tropical regions.

Sarcodina (Amoeboids) – Amoebae

  • Move via pseudopods (false feet); crawl rather than swim.
  • Habitat: typically bottom-dwelling in moist environments; amoebas crawl slowly and are often found at the bottom of containers.
  • Notable human pathogens and examples:
    • Entamoeba histolytica: causes amoebic dysentery; common intestinal parasite in the United States and globally; treated with metronidazole.
    • Entamoeba coli: nonpathogenic, often used as a commensal in discussions.
    • Naegleria fowleri: brain-eating amoeba; causes primary amoebic meningitis (PAM); often fatal; associated with nasal exposure to warm freshwater (e.g., neti pots); historically rare but highly lethal.
    • Acanthamoeba spp.: can cause encephalitis and keratitis; associated with contact lens use and contaminated water.
    • Balantidium coli is a ciliate, not an amoeba (included here as a note: amoebae vs ciliates exist as separate groups).
  • Balantidium and other ciliates:
    • Balantidium coli is a ciliate and the only known ciliate that commonly infects humans; ciliates swim with numerous cilia around the cell surface.
  • Trophozoite versus cyst focus:
    • Amoebae that infect humans often have trophozoite (active) and cyst (resting) stages; cysts enable survival outside the host.

Ciliophora (Ciliates)

  • Characteristic feature: numerous cilia used for locomotion and feeding.
  • Balantidium coli: an example of a ciliate that can infect humans; considered a zoonotic parasite primarily associated with pigs.
  • Relationship to protozoan disease: less commonly associated with human illness compared to Giardia, Entamoeba, and Naegleria; nonetheless, ciliates are an important part of protozoan diversity.

Clinical context and public health relevance

  • Intestinal protozoa of major concern in the United States include Entamoeba histolytica, Giardia lamblia, and Balantidium coli (the latter less common).
  • Intestinal protozoa transmission typically occurs via ingestion of cysts in contaminated water.
  • The distinction between bacterial diarrhea and protozoal diarrhea:
    • Bacterial diarrhea from contaminated water typically begins within about 1 day after exposure.
    • Protozoal diarrhea (e.g., Giardia) often presents later (2–4 days) and can be more severe or prolonged in some cases.
  • The neti pot case highlights route of exposure for Naegleria fowleri and nasal entry leading to PAM; emphasizes caution with water used in nasal irrigation.

Practical implications and connections to broader themes

  • Ecology and public health: nutrient pollution and eutrophication connect ecosystem health with human health (fish kills, toxins, shellfish safety).
  • Environmental management: reducing nutrient runoff (nitrogen and phosphorus) is key to preventing harmful algal blooms and protecting water quality.
  • Biotechnology and sustainability: algae-based products, including lipids for biodiesel, showcase potential but require engineering, economics, and lifecycle assessment to be viable.
  • Ethical and policy considerations:
    • Biofuel initiatives must balance energy needs with environmental impact and land-use implications.
    • Domestic and agricultural practices (e.g., poultry farming) influence water quality and ecosystem health.
    • Pet ownership and outdoor cats have ecological effects, including toxoplasmosis risks to wildlife and humans.
  • Practical lab notes:
    • Agar remains a staple for solid media; its compatibility with many lab workflows reduces contamination and simplifies culturing.
    • Diatomaceous earth provides multiple functional roles in filtration, polishing, and pest control, with safety considerations for humans when used in gardening or consumer products.
  • The scope of protozoan diseases is largely tropical and travel-linked; however, vigilance is still important due to potential range shifts with climate change and vector distribution.

Summary of key numerical references and explicit facts (LaTeX-formatted)

  • Global oxygen production: 70\% from algae/cyanobacteria; 30\% from terrestrial plants.
  • Current atmospheric oxygen: 21\%.
  • Dinosaur-era oxygen: approximately 15\%\text{-}16\%.
  • Agar melting/solidification: dissolve at about 90^{\circ}C; solidifies around 40^{\circ}C.
  • Lipid content in some algae (potentially): up to 50\% of dry weight.
  • Agar price spike (historical anecdote): from about 100\,\$/\text{pound} to nearly 500\,\$/\text{pound} during shortages.
  • Chlorination and cyst resistance (Cryptosporidium): cysts are resistant to standard chlorination; high chlorine doses may be needed, and filtration is important.
  • Pool chlorine dynamics (example values): shock to about 10\text{ ppm}, then typical maintenance around 3\text{ ppm}; chloramines indicate chlorine has reacted with organics and is no longer effectively disinfecting.
  • Red tide and shellfish toxins: toxins can accumulate in shellfish (oysters, clams) even when water toxins are not directly affecting humans in the water.

Connections to prior topics and real-world relevance

  • The discussion links microbial ecology to environmental management (nutrient pollution and eutrophication) and public health (waterborne diseases like cryptosporidiosis and Giardia-related symptoms).
  • It illustrates how lab tools (agar, media) emerge from natural products (seaweed) and how industry drives scientific practice (agar use in labs, DE in filtration and cosmetics).
  • It highlights the importance of vector biology in disease ecology (-malaria via Anopheles, Chagas via kissing bugs, sleeping sickness via Trypanosoma; toxoplasmosis via cats).
  • It emphasizes translational relevance: algae-based products, biofuels, and nutraceuticals intersect science with industry, policy, and ethics.

Key terms to remember

  • Apicomplexa (Sporozoa); Plasmodium; Toxoplasma; Cryptosporidium; life cycle complexity; host specificity.
  • Mastigophora (Flagellates); Giardia; Trypanosoma; Leishmania; Trichomonas.
  • Sarcodina (Amoebae); Entamoeba histolytica; Naegleria fowleri; Acanthamoeba; pseudopods.
  • Ciliophora (Ciliates); Balantidium coli; cilia-based motility.
  • Balantidium coli as a human-infecting ciliate; Naegleria fowleri and PAM; cyst vs trophozoite.
  • Foraminifera (calcium carbonate shells) as part of protozoa with fossilized skeletal remains.
  • Diatoms; diatomaceous earth; silica-based cell walls; abrasive and filtration uses.
  • Algal blooms; eutrophication; red tide; Pfiesteria; marine toxins; ASP and PSP; heating resistance of toxins.
  • Agar; carrageenan; alginate; seaweed extracts; lab media.
  • Spirulina as a cyanobacterium; confusion with algae in popular discourse.
  • Biofuels from algae; lipid fraction; scale-up challenges; Exxon/Volvo as industry players.
  • Toxoplasma gondii; TORCH testing; congenital infections; cat as intermediate host.
  • Cryptosporidium outbreak and water treatment challenges; HIV-related risks.
  • Neti pot exposure and Naegleria fowleri entry route.