![[Graphical abstract Bioresource Technology 2024] [Graphical abstract Bioresource Technology 2024]](/sites/default/files/2024-07/GraphicalAbstractV4.jpg)
A study published in the journal Bioresource Technology by the group led by Auxiliadora Prieto at the Centro de Investigaciones Biológicas Margarita Salas (CSIC) demonstrates the adaptability of the photosynthetic bacterium Rhodospirillum rubrum to environmental conditions, obtaining metabolically enhanced variants for syngas fermentation. The study describes genotypic changes driven by syngas exposure as selective pressure and alteration in protein expression profile after an evolutionary process of 200 generations.
Municipal, agricultural, or food waste, and sewage sludge from wastewater treatment plants, contain a substantial fraction of carbon that can be efficiently valorized. Although different microorganisms can easily digest organic waste, certain recalcitrant compounds require more complex processes such as gasification or pyrolysis. This process leads to the production of syngas, whose composition includes CO, H2, and CO2. In this context, R. rubrum stands out as one of the few bacteria able to thrive in syngas environments and produce bioplastics such as polyhydroxyalkanoates (PHA), which have attracted increasing biotechnological interest in recent years. Moreover, either by photofermentation of organic acids and carbohydrates or by CO oxidation, this bacterium can produce H2.
Hernández-Herreros et al. have studied the metabolic mechanisms involved in the increased hydrogen production in the adapted variants compared to the wild-type strain. Different point mutations were identified through genomic analysis, highlighting a change in the gene expression regulator PpsR. Previous works by this group indicated that the PpsR regulator is responsible for modulating the transcription of genes involved in the synthesis of bacteriochlorophyll and carotenoids, as well as genes encoding the antenna complex, the main structure responsible for light harvesting.
Moreover, proteomic analysis revealed that the adapted variants improved their H2 production capacity due to increased CO dehydrogenase enzyme complex expression, allowing more active CO oxidation. On the other hand, overexpression of the photosynthetic system and metal cofactors essential for pigment biosynthesis was observed.
These results open a new research scenario for the production of H2 as a strategy for the valorization of complex waste through CO oxidation using R. rubrum as a biocatalyst and pave the way for new research lines aimed at mitigating the toxic effects of CO through metabolic approaches.
The research presented in this paper has been funded by the CSIC Interdisciplinary Thematic Platform (PTI+) Sustainable Plastics Towards a Circular Economy (PTI-Susplast+), the Community of Madrid, and the Spanish Ministry of Science and Innovation.
Reference: Boosting hydrogen production in Rhodospirillum rubrum by syngas-driven photoheterotrophic adaptive evolution. Natalia Hernández-Herreros, Alberto Rodríguez, Beatriz Galán y M. Auxiliadora Prieto (2024) Bioresource Technology 406 (130972) https://doi.org/10.1016/j.biortech.2024.13097