Growth and hydrogen production of the cyanobacterium Synechocystis sp. PCC 6803 in a marine salt medium

The cyanobacterium Synechocystis sp. PCC 6803 is a promising candidate for sustainable hydrogen production due to its ability to generate hydrogen under fermentative conditions. This study investigates the impact of marine salt (35 g L−1) supplementation in BG11 medium on the growth, biochemical composition, and hydrogen production of Synechocystis sp. PCC 6803. Cultures were subjected to a three-phase experimental design consisting of growth, nitrogen starvation, and dark fermentation. Marine salt supplementation did not influence growth rate during the initial phase and did not hinder biomass accumulation under nitrogen-deprived conditions. Biochemical analyses revealed that marine salt did not affect carbohydrate accumulation but decreased polyhydroxybutyrate accumulation, while protein content remained comparable between treatments. Notably, cultures grown in marine salt-supplemented media exhibited moderately enhanced hydrogen production, achieving up to 9.14 ± 0.62 mL g-1 dry weight over four days—slightly higher than in control cultures. Our results indicated that carbohydrates accumulated during the nitrogen starvation phase are only partially utilized for hydrogen production during the subsequent phase of dark fermentation, and that more than 90% of the hydrogen produced occurs within the first 3 days. These findings suggest that marine salt not only supports acceptable growth of Synechocystis but also enhances its hydrogen production potential by improving the sustainability of the process.