Raab et al. 2024 — Arsenolipids in Chlamydomonas reinhardtii
This study reports the arsenic speciation profile of the green microalga Chlamydomonas reinhardtii, cultivated under controlled laboratory conditions, with particular focus on lipid-soluble arsenic compounds (arsenolipids). The key finding is the first reported detection of arsenosugar phospholipid with a phytol side chain (AsSugPhytol) in any organism. Approximately 57% of total arsenic in C. reinhardtii was present as arsenolipids, a much higher proportion than typically found in macroalgae such as Saccharina latissima used for comparison. The study contributes to understanding how arsenic accumulates in microalgae and what speciation is present in algae-derived food ingredients.
Key numbers
- Matrix: Chlamydomonas reinhardtii (green microalga, freshwater), laboratory culture
- Total arsenic: specific concentration values reported at trace levels; arsenolipid fraction = 57% of total As
- New compound: AsSugPhytol (arsenosugar phospholipid with phytol chain) — first report in any organism
- Other arsenolipids detected: arsenosugar glycerophospholipid, arsenohydrocarbon derivatives
- Comparison: Saccharina latissima (edible brown macroalga, seaweed) had different arsenolipid profile; lower arsenolipid fraction, different compound distribution
- Analytical method: HPLC-ICP-MS for total As and inorganic speciation; HPLC-ESI-MS/MS for arsenolipid structural characterization
- iAs fraction: present but a minor component in C. reinhardtii; the arsenolipid fraction dominated
Methods (brief)
Laboratory cultivation of C. reinhardtii in standard algal medium; biomass harvested and subjected to lipid extraction (chloroform:methanol), followed by HPLC-ICP-MS for As speciation in both aqueous and lipid fractions and HPLC-ESI-MS/MS for molecular characterization of arsenolipids. LOD for ICP-MS speciation not specified in extracted content.
Implications
Certification: Microalgae (Chlorella, Spirulina, C. reinhardtii-derived products) are increasingly used in food and dietary supplements. Arsenic speciation in these ingredients is critical for regulatory compliance, especially as EU limits distinguish total As and may evolve toward iAs-specific limits. The high arsenolipid fraction in C. reinhardtii (vs. macroalgae) suggests the organic fraction dominates, which is relevant to bioaccessibility and risk assessment.
Courses: Demonstrates that “total arsenic” measurement in algae-derived ingredients can be dominated by arsenolipids rather than iAs; critical case for the iAs vs. tAs distinction in ingredient pages.
App: Arsenic in algae/microalgae ingredients should be flagged as requiring speciation; total As alone may overestimate iAs risk.