Enhancement of phototrophic hydrogen production by Rhodobacter sphaeroides ZX-5 using a novel strategy — shaking and extra-light supplementation approach

Biohydrogen has gained attention due to its potential as a sustainable alternative to conventional methods for hydrogen production. In this study, the effect of light intensity as well as cultivation method (standing- and shaking-culture) on the cell growth and hydrogen production of Rhodobacter sphaeroides ZX-5 were investigated in 38-ml anaerobic photobioreactor with RCVBN medium. Thus, a novel shaking and extra-light supplementation (SELS) approach was developed to enhance the phototrophic H2 production by R. sphaeroides ZX-5 using malate as the sole carbon source. The optimum illumination condition for shaking-culture by strain ZX-5 increased to 7000–8000 lux, markedly higher than that for standing-culture (4000–5000 lux). Under shaking and elevated illumination (7000–8000 lux), the culture was effective in promoting photo-H2 production, resulting in a 59% and 56% increase of the maximum and average hydrogen production rate, respectively, in comparison with the culture under standing and 4000–5000 lux conditions. The highest hydrogen-producing rate of 165.9 ml H2/l h was observed under the application of SELS approach. To our knowledge, this record is currently the highest hydrogen production rate of non-immobilized purple non-sulphur (PNS) bacteria. This optimal performance of photo-H2 production using SELS approach is a favorable choice of sustainable and economically feasible strategy to improve phototrophic H2 production efficiency.