The anoxic switch: Strain variation in H2 exchange during repeated illumination after dark anoxia

First sustained illumination after prolonged dark anoxia yields higher H2 production rates than later cycles in most Chlamydomonas reinhardtii cultures, with strain ratios ranging from 0.63 to 17.48.

• Why it matters: Hydrogen exchange during light transitions can record physiological history, but the extent and drivers of strain-to-strain variation in the anoxic switch remain unclear.
• What they did: Using membrane-inlet mass spectrometry, the study compared 54 cultures from 17 strains across sequential irradiances and 48 cultures from 15 strains across seven repeated 2 min light/3 min dark cycles.
• The result: For the primary early-response 30 s endpoint, first sustained-light rates exceeded mean cycles 5–7 in 43 of 48 cultures, and strain explained most variance in first-to-later ratios, suggesting PSII photosynthetic control as a candidate mechanism.

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