Microalgae · Field note
Spirulina Is a Cyanobacterium — What That Actually Means
Spirulina is a photosynthetic bacterium, not a plant-like alga — and that single fact reshapes how you feed, buffer, and protect the culture.
- "Spirulina" is really Arthrospira, a prokaryotic cyanobacterium — no nucleus, no chloroplast
- It uses blue phycocyanin (~10–20% DW) to harvest light; green algae lack this pigment
- Native to alkaline soda lakes; thrives near pH 9.5–10.5, tolerant to ~11
The organism sold as “Spirulina” is a filamentous cyanobacterium in the genus Arthrospira (chiefly A. platensis and A. maxima). The market name is a historical mix-up: it was once classified in the genus Spirulina, and the label stuck. That taxonomy is not pedantic trivia — it changes the biology you are cultivating. Cyanobacteria are prokaryotes: they have no nucleus and no chloroplast. Their photosynthetic machinery sits on internal thylakoid membranes within the cell itself.
Three practical consequences flow from this. Pigments: cyanobacteria harvest light with phycobiliproteins — most famously the brilliant blue phycocyanin, which can reach roughly 10–20% of dry weight. Cell wall: Arthrospira has a soft peptidoglycan wall rather than the tough cellulose wall of green algae, which is why Spirulina is digestible without the cell-cracking step Chlorella needs. Niche: Arthrospira evolved in warm, highly alkaline soda lakes rich in bicarbonate, thriving near pH 9.5–10.5 and tolerating values up to about 11.
That alkaline preference is a gift to the grower. High pH is a built-in contamination defense: the same water chemistry Spirulina loves is hostile to most bacteria, fungi, and grazing protozoa. It also dictates the medium — Spirulina is fed bicarbonate rather than pumped CO2 alone, because dissolved bicarbonate is both its carbon source and its pH buffer. For an autonomous system like Algaephyte, knowing you are tending a cyanobacterium is what justifies the whole control philosophy: alkaline setpoints, bicarbonate dosing for carbon and pH together, and a light model tuned to a filament that self-shades.
Research context and limitations
This note belongs to Algaephyte cultivation and control. Algaephyte and Cyanoflow are research concepts in development. Architecture descriptions are design goals; simulations are not laboratory measurements. Older numerical, biological and safety statements need checking against the relevant source and conditions.
Source-linked reading
For optical measurements and biomass proxies, see Schagerl et al. (2022), the roadmap for reliable microalgal biomass and vitality measurements. This is methodological background, not verification of every claim in this note.
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Research methods and topic directory · Definitions of cultivation, sensing and single-cell terms · The proposed Algaephyte cultivation architecture · All cultivation and control notes
Scientific and safety limitations: visual appearance and high pH do not certify culture identity or food safety.
Connect this guide to the wider research
This supporting note connects to microalgae cultivation fundamentals, photobioreactor design and measurement, and Algaephyte’s proposed cultivation architecture. Follow those pillars for related light, chemistry, sensor and control explanations.
Methodology and evidence status · Scientific definitions · Safety and scope.