Towards biohydrogen overproduction and valorization of food waste by genetic engineering of Rhodobacter capsulatus

Abstract

Non-sulfur red bacteria, such as Rhodobacter capsulatus, produce H2 through photofermentation via nitrogenase. These bacteria offer several advantages over other hydrogen bioproduction systems, including high substrate conversion efficiency, the use of a wide variety of carbon sources, the ability to operate under environmental conditions, reduced energy consumption, and high purity of the hydrogen produced. Despite these advantages, higher production rates and more economical carbon sources are required to compete with conventional H2 production methods. For this reason, our ongoing work focuses on two main objectives: genetically redesigning R. capsulatus to increase its H2 production rates, and optimizing and improving the process by valorizing the material and energy content of food waste.

In the H2 production experiments with R. capsulatus, both the wild-type strain and a mutant defective in uptake hydrogenase (ΔhupAB) were evaluated. Process water obtained from the hydrothermal carbonization of food waste and a minimal RCV medium were used as substrates in the photofermentation process. The experiments were carried out in batch mode under continuous illumination. The highest levels of H2 production were observed under the condition where the hupAB mutant was growing in RCV medium without a nitrogen source (almost 110 mL of H2/gCOD). However, H2 production values were similar to those obtained using process water as a substrate during the first 24 hours, thereby demonstrating that R. capsulatus can produce H2 from food waste.