Photosynthetic bacteria Marichromatium purpuratum LC83 enhances hydrogen production by Pantoea agglomerans during coupled dark and photofermentation in marine culture

• A marine photosynthetic bacterium was isolated and identified as Marichromatium purpuratum.
• Property analysis of M. purpuratum LC83 was performed.
• M. purpuratum LC83 improved the fermentative liquid conditions of P. agglomerans BH-18.
• Hydrogen production and glucose consumed by coupled fermentation were higher than pure control.
• The optimum inoculation ratio was 1/8 (strains BH-18/LC83) in coupled dark and photofermentation.

A marine photosynthetic bacterial strain LC83 was isolated from bathing beach sludge and identified as Marichromatium purpuratum using light microscopic examination, Biolog tests, and 16S rRNA gene sequence analysis. The strain is a salt- and alkali-tolerant, vitamin-independent facultative anaerobe with an optimum sodium chloride (NaCl) concentration of 30‰, initial optimum pH of 7.0–8.0, optimum temperature of 30 °C, and optimum light intensity of 80–160 μmol/m2/s. The addition of M. purpuratum LC83 to the dark fermentation of Pantoea agglomerans BH-18 for 8 h clearly improved the pH and the oxidation–reduction potential of the fermentative liquid, retarded the reduction in glucose, and maintained the balance between the glucose generated photosynthetically by the photosynthetic bacteria and those consumed by the fermentative bacteria in the early stage of coupled fermentation. The addition of photosynthetic bacteria to dark fermentation at 8 h improved the fermentative liquid conditions in favor of hydrogen production. The yield of hydrogen and the amount of glucose consumed by the coupled fermentation were also both higher than during pure fermentation by P. agglomerans BH-18. The optimum inoculation ratio was 1/8 (strains BH-18/LC83). The coupled dark and photofermentation of M. purpuratum LC83 and P. agglomerans BH-18 is a feasible way of improving the level of hydrogen produced in marine culture.