Enhanced hydrogen production by a newly described heterotrophic marine bacterium, Vibrio tritonius strain AM2, using seaweed as the feedstock

• The marine vibrio shows a greater ability to produce bioH2 under saline conditions.
• The maximum molar yield of bioH2 was recorded as 1.7 mol H2/mol mannitol.
• The vibrio can produce bioH2 from powdered brown seaweed as a feedstock.

To achieve more stable bio-hydrogen (bioH2) production from non-food feedstocks, stable feedstock preparations of marine biomass and an efficient bioH2 system using marine bacteria under saline conditions are two important key technologies that needed to be developed. Vibrio tritonius strain AM2, which was isolated from the gut of a marine invertebrate, was cultured under various conditions in marine broth (at initial 2.25% (w/v) NaCl) supplemented with mannitol, a seaweed carbohydrate, to evaluate its hydrogen production. The maximum molar yield of bioH2 was recorded as 1.7 mol H2/mol mannitol at pH 6 and 37 °C. The mannitol-grown cells had higher yields of bioH2 than the glucose-grown cells in the pH range 5.5–7.5. Compared to glucose, mannitol might be a better substrate for bioH2 production using strain AM2. Fermentation product profiling revealed that strain AM2 might be utilising the formate-hydrogen pathway for bioH2 production. Furthermore, strain AM2 was able to produce hydrogen from powdered brown macroalgae containing 31.1% dry weight of mannitol. The molar yield of hydrogen reached 1.6 mol H2/mol mannitol contained in the seaweed feedstock. In conclusion, strain AM2 has the ability to produce hydrogen from mannitol with high yields even under saline conditions.