Iron limitation – A perspective on a growth-restricted cultivation strategy for a H2 production system using the diazotrophic cyanobacterium Nostoc PCC 7120 ΔhupW

H2 is a promising carbon-free alternative to fossil fuels, and can be photoautotrophically produced by cyanobacteria. Despite efforts to increase cyanobacterial H2 production by genetic engineering and technical optimization the yield remains economically non-viable. Recent studies have therefore demanded the impairment of growth to reallocate more carbohydrates into biofuel biosynthesis, and nutrient limitation may be a strategy to achieve that. Here we show that limitation of Fe in the filamentous and heterocystous mutant strain Nostoc PCC 7120 ΔhupW resulted in a 5.3-fold lower chlorophyll a concentration as compared to the controls during four-week cultivation. The Fe-limited filaments contained a heterocyst frequency at ~6% and a 4-fold higher specific carbohydrate concentration as compared to the control cultures. We discuss whether Fe-limiting conditions leading to an accumulation of carbon storage compounds could be used as a heterocyst based H2 production system. [Display omitted] •A cultivation strategy for improved heterocyst-based H2 production is proposed.•The heterocyst frequency remained constant during Fe-limited growth.•The carbohydrate concentration increased in filaments during iron limitation.•Slower growth for Nostoc was determined during iron limitation.