Green algae show varied hydrogen responses when light returns after anoxia

What the study found

In a bioRxiv preprint, Kikoine and Yacoby report that first-light hydrogen production rates exceeded later rates in most cultures tested after dark anoxia. They used membrane-inlet mass spectrometry to compare 54 independently grown cultures from 17 strains across sequential light intensities, and 48 cultures from 15 strains across seven cycles of two minutes of light and three minutes of darkness.

For the primary 30-second early-response measure, the first sustained-light rate exceeded the mean rate in cycles five through seven in 43 of 48 cultures. The ratio of strain-average first to later rates was above one in 14 of 15 strains and ranged from 0.63 to 17.48. G1122 was the only strain with higher later rates. The authors report that strain accounted for most of the variation in culture-level ratios.

Why it matters

The findings extend the pattern previously described in Chlamydomonas reinhardtii to a broader selection of green microalgae. In that species, the first-light response has been linked to photosynthetic control involving photosystem II. The authors suggest that strains with different response magnitudes could help test whether that control explains the observed variation.

Limits and unknowns

The predominance of higher first rates remained when the authors used alternative measurement windows or excluded cultures with elevated oxygen before illumination, although the magnitude depended on the window. Oxygen and nominal carbon dioxide signal changes varied among strains, but neither showed a detected cross-strain correlation with the hydrogen ratio.

The abstract does not provide detailed growth conditions, uncertainty estimates or full statistical methods. It also does not establish that photosystem II control causes the differences among strains; that remains a question for further testing.