Fig. 6

Phototrophic hydrogen production by non-growing PVA-immobilised R. palustris. Nitrogen-free minimal media with 50 mM glycerol used for cultivation under illumination in test bioreactors in batch mode (a–c), and continuous mode at a dilution rate of 0.01 h⁻¹ (d). Hydrogen volume was normalised to biomass in reactor, reported as specific hydrogen production (a, d). Equal biomass was loaded into planktonic and immobilised reactors at the start of the experiment and concentration was tracked to confirm lack of growth and to monitor cell leakage from PVA beads (b). Glycerol concentration was measured to track carbon consumption (c). Error bars represent SD for minimum 3 replicate reactors. For long-term continuous photofermentation (d), varying quantities of beads were loaded into single reactors under both axenic (i: 100 g, ii: 160 g) and non-axenic conditions (iii: 160 g)