Wild-Harvested Blue-Green Algae Is Often Not Spirulina

Executive Summary

"Wild-harvested" reads as a quality signal in most botanical categories. In cyanobacteria it inverts, and not for the reason the phrase suggests.

The issue is not only that wild biomass is dirtier than farmed biomass. The best-known wild-harvested product is a different organism. What gets skimmed off Upper Klamath Lake and sold as blue-green algae is Aphanizomenon flos-aquae — a different genus from commercial spirulina, harvested from open water where Microcystis aeruginosa, the microcystin producer, blooms as a matter of course. The toxin producer comes up in the net. In the survey that prompted Oregon to set a limit, microcystins were found in 85 of 87 samples, and 63 of them — 72% — exceeded 1 µg/g^[1]Gilroy et al. (2000). Assessing potential health risks from microcystin toxins in blue-green algae dietary supplements. Environmental Health Perspectives 108(5):435–439 Link.

Against that, the cultivated organism has something better than a clean test result. It has no genetic capacity to produce microcystins at all. Across 22 Limnospira and Arthrospira genomes, homology searches against three reference microcystin gene clusters returned no hits, and antiSMASH detected no non-ribosomal peptide synthase or polyketide synthase clusters of any kind^[2]Pinchart et al. (2024). The genus Limnospira contains only two species, both unable to produce microcystins: L. maxima and L. platensis. iScience 27(9):110845 Link.

That single fact reframes the whole specification question:

Any microcystin in a spirulina lot came from a contaminant organism, not from the crop.

Which is why "cultivated" is not a specification. It is a large reduction in risk that still depends on pond management and on testing. Testing has its own problems: the usual screening method for microcystins has over-reported in at least one documented case, and there is no harmonised limit.

1. Two organisms, one shelf label

Commercial spirulina is a cultivated filamentous cyanobacterium grown in managed alkaline medium. Its tolerance for pH up to about 12 is the reason it can be farmed as a near-monoculture at all: very little else grows there, which structurally suppresses contamination by other photosynthetic organisms^[6]Roussel et al. (2023). Monospecific renaming within the cyanobacterial genus Limnospira (Spirulina) and consequences for food authorization. Journal of Applied Microbiology 134(8):lxad159 Link.

Klamath AFA is the opposite proposition. It is a natural bloom, harvested from a lake, in a system where the operator controls neither the species composition nor the timing. Microcystis aeruginosa co-occurs with A. flos-aquae there routinely, and the 1996 Klamath bloom is what triggered the survey work and Oregon's subsequent 1 µg/g regulatory limit^[1]Gilroy et al. (2000). Assessing potential health risks from microcystin toxins in blue-green algae dietary supplements. Environmental Health Perspectives 108(5):435–439 Link^[3]Pinchart et al. (2023). Microcystins and Cyanobacterial Contaminants in the French Small-Scale Productions of Spirulina (Limnospira sp.). Toxins 15(6):354 Link.

The distinction is not a matter of farming standards. Selective cultivation medium excludes competitors; open-lake skimming cannot.

2. The genus cannot make the toxin

This is the strongest claim in the article, and it is recent.

Pinchart et al. assembled three new metagenome-assembled genomes from commercial spirulina cultures and compared them with 19 reference genomes. They ran blastn against the microcystin gene clusters of Microcystis aeruginosa K-139, Planktothrix agardhii NIVA-CY 126/8 and Anabaena sp. 90. No hits. Blastp and tblastn against Mcy proteins found no related non-ribosomal peptide synthases or polyketide synthases. antiSMASH 7.1.0 across all 22 strains detected no NRPS or PKS clusters whatsoever^[2]Pinchart et al. (2024). The genus Limnospira contains only two species, both unable to produce microcystins: L. maxima and L. platensis. iScience 27(9):110845 Link.

Their conclusion is unhedged: none of the 22 strains has the genetic capacity to produce microcystins or any other cyanotoxin with a known biosynthesis cluster.

This also retires an older complication. Arthrospira fusiformis had been cited in the literature as a microcystin producer, on the strength of two studies by the same author. That association is now regarded as erroneous — attributed in part to the taxonomic reclassification of contaminant strains rather than to the spirulina itself^[7]Mastroleo et al. (2026). Cyanosphere of commercial spirulina (Limnospira spp.) cultures and characterization of a dominant cyanobacterial contaminant (Sodalinema sp.). Journal of Applied Phycology (online 7 May 2026) Link.

For a formulator, the practical translation is that a microcystin result on a spirulina CoA is a contamination finding, with all that implies: it points at pond hygiene, at a co-cultured organism, or at the assay — never at the strain you bought.

3. What the cultivated-product data actually shows

Two datasets, pulling in opposite directions. Both belong in a procurement decision.

The reassuring one is much larger. Pinchart et al. compiled microcystin results from 95 French small-scale producers across 2013–2021: 623 dry spirulina samples and 105 culture samples, by ELISA. Of the dry-product results, 42% were below the 0.15 ppm limit of quantification and more than 99% were below the 1 ppm regulatory level. Mean content across the whole period was 0.21 ppm MC-LReq dry weight — with results under the LOQ conservatively counted as 0.075 ppm rather than zero. At the producers' own recommended 3 g daily dose, that works out to roughly 10 ng/kg bw/day^[3]Pinchart et al. (2023). Microcystins and Cyanobacterial Contaminants in the French Small-Scale Productions of Spirulina (Limnospira sp.). Toxins 15(6):354 Link.

Culture-water samples from 2017 averaged 0.39 ppb, below the 1 ppb WHO guideline value for MC-LR in drinking water^[3]Pinchart et al. (2023). Microcystins and Cyanobacterial Contaminants in the French Small-Scale Productions of Spirulina (Limnospira sp.). Toxins 15(6):354 Link.

The uncomfortable one is much smaller. Rhoades et al. examined five retail products — two supplements, three spirulina-supplemented foods — by ELISA and found microcystins in all five. Estimated daily exposures were 900 ng for spirulina powder and 1000 ng for tablets, against tolerable daily intakes of 200 ng (infants, 5 kg), 800 ng (children, 20 kg) and 2400 ng (adults, 60 kg). The powder and tablets exceeded the infant and child TDI. The supplemented foods — a cereal bar, tahini with honey, a cocoa-praline — ran 4700–5700 ng and exceeded the adult TDI as well^[4]Rhoades et al. (2023). Microbiota and Cyanotoxin Content of Retail Spirulina Supplements and Spirulina Supplemented Foods. Microorganisms 11(5):1175 Link.

Dataset	n	Method	Headline result
Blue-green algae (AFA) supplements, 2000[1]Gilroy et al. (2000). Assessing potential health risks from microcystin toxins in blue-green algae dietary supplements. Environmental Health Perspectives 108(5):435–439 Link	87	HPLC + ELISA	72% above 1 µg/g
French small-scale spirulina, 2013–2021[3]Pinchart et al. (2023). Microcystins and Cyanobacterial Contaminants in the French Small-Scale Productions of Spirulina (Limnospira sp.). Toxins 15(6):354 Link	623 dry	ELISA	mean 0.21 ppm; >99% under 1 ppm
Retail spirulina products[4]Rhoades et al. (2023). Microbiota and Cyanotoxin Content of Retail Spirulina Supplements and Spirulina Supplemented Foods. Microorganisms 11(5):1175 Link	5	ELISA	detected in all five

The first two rows use different measures, so they cannot be compared directly, but the difference in direction is clear: most wild-harvested AFA samples in 2000 exceeded 1 µg/g, while more than 99% of the French cultivated samples were below it. The third row is the reason "cultivated" cannot be left to stand on its own.

Rhoades et al. state their own constraint plainly: with five samples and no toxicological testing, "it is impossible to accurately determine the risk to human health"^[4]Rhoades et al. (2023). Microbiota and Cyanotoxin Content of Retail Spirulina Supplements and Spirulina Supplemented Foods. Microorganisms 11(5):1175 Link. Treat it as a signal that the category is not self-policing, not as a prevalence estimate.

4. The source of microcystin in cultivated spirulina has not been identified

This matters before you write a limit into a contract.

Pinchart et al. found no correlation between microcystin levels and cyanobacterial contaminant populations across their dataset, and say directly that the study could not identify the contaminant or contaminants responsible. They note genomic analysis would be needed to do so^[3]Pinchart et al. (2023). Microcystins and Cyanobacterial Contaminants in the French Small-Scale Productions of Spirulina (Limnospira sp.). Toxins 15(6):354 Link.

Rhoades et al. report an unexplained result. Their 16S rRNA amplicon sequencing identified no toxic cyanobacterial species in the products — yet ELISA returned significant microcystin concentrations in every one^[4]Rhoades et al. (2023). Microbiota and Cyanotoxin Content of Retail Spirulina Supplements and Spirulina Supplemented Foods. Microorganisms 11(5):1175 Link.

The best-characterised contaminant does not appear to be a toxin producer. Mastroleo et al. identified Sodalinema sp. as a recurrent dominant cyanobacterial contaminant across six commercial cultivars, then analysed five available Sodalinema genomes plus their own new metagenome-assembled genome: no cyanotoxin synthesis genes found^[7]Mastroleo et al. (2026). Cyanosphere of commercial spirulina (Limnospira spp.) cultures and characterization of a dominant cyanobacterial contaminant (Sodalinema sp.). Journal of Applied Phycology (online 7 May 2026) Link. Contaminant biovolumes are in any case tiny — on the order of a thousandth, with edible Limnospira generally above 99% of total biovolume^[3]Pinchart et al. (2023). Microcystins and Cyanobacterial Contaminants in the French Small-Scale Productions of Spirulina (Limnospira sp.). Toxins 15(6):354 Link.

So there are two live explanations for positive microcystin results in cultivated spirulina, and the literature has not settled between them: an unidentified producer organism, or a screening assay reporting something that is not microcystin. The next section covers the second possibility.

5. The test method changes the result

Pinchart et al. record a specific incident. In 2021, four batches of French spirulina were flagged above the 1 ppm regulatory level by ELISA. Before the producers destroyed the product, they submitted those four batches plus a fifth (which had screened below the limit) for UHPLC-MS/MS confirmation.

The confirmatory values came back lower than the ELISA values^[3]Pinchart et al. (2023). Microcystins and Cyanobacterial Contaminants in the French Small-Scale Productions of Spirulina (Limnospira sp.). Toxins 15(6):354 Link.

That is a documented case where a screening immunoassay result, if acted on, would have led to destruction of material that the confirmatory method measured lower. ELISA is fast, cheap and appropriate as a screen — it is what generated the large French dataset in the first place. It is not a release assay, and it is not what a disputed result should be settled on.

Two consequences for anyone writing a microcystin clause:

1. Name the method. "Microcystins ≤1 ppm" without a method is not one specification, it is two, and they disagree in a direction that costs the supplier.
2. Name a confirmatory method and a trigger. UHPLC-MS/MS on any screening result above some fraction of the limit turns an argument into a procedure.

There is also no harmonised limit to anchor to. The 1 µg/g figure in near-universal use is an Oregon state limit from 1997, generalised by the industry into a de facto global specification^[1]Gilroy et al. (2000). Assessing potential health risks from microcystin toxins in blue-green algae dietary supplements. Environmental Health Perspectives 108(5):435–439 Link^[3]Pinchart et al. (2023). Microcystins and Cyanobacterial Contaminants in the French Small-Scale Productions of Spirulina (Limnospira sp.). Toxins 15(6):354 Link. It is a sensible number with a narrow legal basis. Treat it as a contractual limit you have chosen, not a regulatory threshold you are meeting.

6. The species name on your CoA may be outdated, and the taxonomy is unresolved

This looks like a naming question. It matters commercially because it sits under a named regulatory authorisation.

The split. Nowicka-Krawczyk et al. investigated Arthrospira jenneri, the long-neglected type species of the genus, and found it differs from the commercially cultivated taxa in cell morphology, ultrastructure, ecology and 16S rRNA sequence. They proposed a new genus, Limnospira, to hold the massively produced taxa — leaving A. jenneri behind in Arthrospira^[5]Nowicka-Krawczyk et al. (2019). Detailed characterization of the Arthrospira type species separating commercially grown taxa into the new genus Limnospira (Cyanobacteria). Scientific Reports 9:694 Link.

The unresolved part. Two groups have since examined how many species Limnospira contains, and reached opposite answers from the same number.

	Roussel et al. 2023[6]Roussel et al. (2023). Monospecific renaming within the cyanobacterial genus Limnospira (Spirulina) and consequences for food authorization. Journal of Applied Microbiology 134(8):lxad159 Link	Pinchart et al. 2024[2]Pinchart et al. (2024). The genus Limnospira contains only two species, both unable to produce microcystins: L. maxima and L. platensis. iScience 27(9):110845 Link
Conclusion	Monospecific — L. platensis, two clades	Two species — L. maxima, L. platensis comb. nov.
Inter-clade ANI	93.4%	93.5–94.6% (OrthoANI)
Intra-clade ANI	—	>98.7% (clade I), >99.0% (clade II)
Inter-clade dDDH	—	49.6–56.6% (70% = species threshold)
Basis	16S, 16S-ITS, ANI, morphology	Phylogenomics, OrthoANI, dDDH, 16S V3–V4

The disagreement is explicit rather than incidental. Pinchart et al. point out that the 93.4% inter-clade value Roussel et al. themselves reported sits below the accepted 95–96% ANI threshold for prokaryotic species delineation — and on that reading it implies two species, not one^[2]Pinchart et al. (2024). The genus Limnospira contains only two species, both unable to produce microcystins: L. maxima and L. platensis. iScience 27(9):110845 Link. Their dDDH values, well under the 70% threshold, point the same way. That is the more orthodox application of prokaryotic criteria, but the question is open and should be described as open.

Why a buyer cares. Under European regulation, only Arthrospira platensis is authorised for consumption — which is precisely why Roussel et al. argue the authorisation should be extended across all Limnospira taxa, including those previously named L. platensis, L. fusiformis, L. indica and L. maxima^[6]Roussel et al. (2023). Monospecific renaming within the cyanobacterial genus Limnospira (Spirulina) and consequences for food authorization. Journal of Applied Microbiology 134(8):lxad159 Link. A live taxonomic dispute sits directly beneath a name in an authorisation.

The practical position is not to pick a side. It is to stop relying on the name alone:

• Keep the authorised name on documentation, with the current genus as a synonym, rather than unilaterally renaming a CoA.
• Specify an identity test, not just an identity claim. Pinchart et al. demonstrated that the V3–V4 hypervariable region of the 16S rRNA gene is sufficient to identify the genus Limnospira and to distinguish its two clades, in agreement with genome-based methods^[2]Pinchart et al. (2024). The genus Limnospira contains only two species, both unable to produce microcystins: L. maxima and L. platensis. iScience 27(9):110845 Link. It is a specifiable, commercially available test.
• Note that morphological contaminant identification is now unreliable on its own. Strains formerly assigned to Phormidium and Geitlerinema have been reclassified across different phylogenetic clades, which means older morphology-based contaminant inventories may be misassigned^[7]Mastroleo et al. (2026). Cyanosphere of commercial spirulina (Limnospira spp.) cultures and characterization of a dominant cyanobacterial contaminant (Sodalinema sp.). Journal of Applied Phycology (online 7 May 2026) Link.

7. What to specify

Layer	Question it answers	Notes
Cultivation method, documented	Selective medium, or open-water harvest?	The single largest risk determinant; a claim, so require evidence
16S V3–V4 sequencing	Is this Limnospira, and which clade?	Sufficient per genome-based comparison[2]Pinchart et al. (2024). The genus Limnospira contains only two species, both unable to produce microcystins: L. maxima and L. platensis. iScience 27(9):110845 Link
Microcystins by ELISA	Screening, batch-level	Fast and cheap; over-reports[3]Pinchart et al. (2023). Microcystins and Cyanobacterial Contaminants in the French Small-Scale Productions of Spirulina (Limnospira sp.). Toxins 15(6):354 Link
UHPLC-MS/MS confirmation	Is a positive screen real?	Trigger it on a defined fraction of the limit
Contaminant taxa monitoring	What else is in the pond?	Molecular, not morphological[7]Mastroleo et al. (2026). Cyanosphere of commercial spirulina (Limnospira spp.) cultures and characterization of a dominant cyanobacterial contaminant (Sodalinema sp.). Journal of Applied Phycology (online 7 May 2026) Link
Batch traceability to pond and harvest date	Where did this biomass come from?	Documentation, not analysis

Microcystin testing tells you about a sample. Knowing which organisms populate the culture, and that the dominant one has no toxin genes, tells you whether a negative result reflects the system or a single lucky sample.

Heavy metals, pesticide residues, PAHs, aflatoxins and the standard microbiological panel are common on spirulina specification sheets. Cyanotoxins are the contaminant class specific to this ingredient category, so check whether your specification covers them.

Where Viridia sits on this

Viridia's spirulina is Arthrospira platensis cultivated in controlled environments and spray dried under controlled conditions, under GMP and HACCP, with analytical testing performed to validated USP, AOAC and ISO methods. The published specification covers protein, loss on drying, ash, bulk density, the full microbiological panel, four heavy metals, pesticide residues, PAH4 and aflatoxins.

For cyanotoxin testing, the questions to settle with any supplier, including us, are which data can be supplied, by which method, and at what limit of quantification.

See the spirulina specification →

Ask about cyanotoxin testing and strain identity →

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