Green reduction of graphene oxide mediated by Sporosarcina pasteurii under harsh conditions, changing the paradigm of rGO production with a non-pathogenic, nanomaterial-resistant bacterium

The reduction of graphene oxide (GO) to reduced GO (rGO) is pivotal for producing graphene-based materials with numerous applications in the fields of electronics, energy storage, sensing, and biomedicine. Traditional reduction methods often involve toxic reagents and high temperatures, which pose significant environmental and safety concerns. Therefore, developing green reduction techniques has become essential. In this work, we demonstrate that the non-pathogenic bacterium Sporosarcina pasteurii is capable of reducing GO under nutrient-deprived aqueous conditions at both low (4 °C) and moderate (30 °C) temperatures. Spectroscopic analyses (UV-vis, Raman, FTIR, and XPS) confirmed the depletion of oxygen-containing functional groups and the partial restoration of the π-conjugated carbon network, indicating the successful reduction of GO. In particular, XPS investigations revealed that epoxide groups are preferentially removed during the bacterial reduction process. Morphological characterization revealed direct association between GO sheets and bacterial cells without compromising cell integrity or long-term viability. Fractionation experiments showed that reduction is mediated by both soluble extracellular components and membrane-associated factors, suggesting a mechanism involving extracellular electron transfer rather than active metabolism. NADH consumption in the presence of GO supports its role as an extracellular electron acceptor, contributing to the cellular redox balance under nutrientlimited conditions. These findings introduce S. pasteurii as a robust biocatalyst for the green, low-cost, and scalable production of rGO under mild conditions.