Wavelength-Specific Reprogramming of the Extracellular Metabolome in Bacterial CdS Biohybrids

Microorganism-semiconductor biohybrids integrate biological metabolism with inorganic light-harvesting materials to enable solar-driven chemical transformations; however, how incident light wavelength regulates extracellular metabolic states remains largely unexplored. Unlike previous hybrid systems that have generally employed fixed-wavelength illumination and bacteria without plant-growth-promoting properties, we investigated wavelength-dependent reprogramming of extracellular metabolism in a CdS biohybrid based on the plant-growth-promoting bacterium Priestia sp. ZJT-3. Sucrose supported the highest bacterial growth, while L-cysteine alleviated Cd²⁺ stress through H₂S-mediated CdS biomineralization, with maximal Cd removal at a cysteine/Cd²⁺ molar ratio of 2:1. Morphological analyses confirmed the formation of surface-associated CdS nanoparticles with an average size of 6.41 nm and a cubic crystal structure. Wavelength-dependent illumination markedly altered the extracellular metabolome, with the number of upregulated metabolites relative to the dark control decreasing in the order of 400, 450, and 520 nm. This pattern suggests that wavelength-dependent CdS excitation modulates photochemical interactions at the biohybrid interface and is associated with distinct bacterial metabolic responses. The 450 nm treatment produced a comparatively moderate metabolic response and was associated with increased levels of plant growth-promoting hormones, whereas 400 nm induced the strongest metabolic remodeling but also greater CdS photocorrosion and cellular morphological perturbation. These findings demonstrate that illumination wavelength can serve as a tunable parameter for regulating extracellular metabolism in bacteria-semiconductor biohybrids, highlighting the potential of such biohybrids for practical applications in areas such as light-controlled metabolite production and bioengineering.