Skin health is a major concern across the world. The Paeonia lactiflora Pall. flower (PLPF) is well-known in China as an edible ornamental flower, that has been traditionally prescribed for the treatment of irregular menstruation and dysmenorrhea. However, its chemical constituents and bioactivities have not been systematically stuided. This study tentatively identified 27 compounds in aqueous and ethanol extracts of PLPF using ultra-performance liquid chromatography with quadrupole time-of-flight mass spectrometry, including four monoterpene glycosides, six phenols, six tannins, ten flavonoids and a hydroxycinnamic acid amide. Online antioxidant and tyrosinase inhibitor screening assays based on post-column bioactivity tests were used to screen for bioactive compounds in the extracts. Online and offline bioactivity assays showed that both extracts exhibited notable antioxidant properties against DPPH, ABTS, and FRAP, potent antiglycation capacity, and significant inhibition of tyrosinase, cyclooxygenase-2, and collagenase. Gallic acid derivatives were the main contributors to the antioxidant and antityrosinase capacity and may also inhibit cyclooxygenase-2 and collagenase, but they exhibited weak antiglycation capacity. The antiglycation effects may be due to the synergistic action of gallic acid and specific flavonoids. PLPF is a promising source of bioactive compounds for the development of natural skin health products.

The escalating global demand for large-scale, cost-effective, and sustainable high-quality protein has positioned single-cell protein (SCP) production from one-carbon (C1) gases as a highly promising solution. In this study, eight chemolithoautotrophic hydrogen-oxidizing bacteria (HOB) were isolated from mangrove sediments. Based on the 16S rRNA gene sequence analysis, they belonged to genera Sulfurimonas, Sulfurovum, Thiomicrolovo, and Marinobacterium. Among these, Thiomicrolovo sp. ZZH C-3 was identified as the most promising candidate for SCP production based on the highest biomass and protein content, and was selected for further characterization. Strain ZZH C-3 is a Gram-negative, short rod-shaped bacterium with multiple flagella. It can grow chemolithoautotrophically by using molecular hydrogen as an energy source and molecular oxygen as an electron acceptor. Genomic analysis further confirmed that ZZH C-3 harbors a complete reverse tricarboxylic acid (rTCA) cycle gene set for carbon fixation, and diverse hydrogenases (Group I, II, IV) for hydrogen oxidation. Subsequently, its cultivation conditions and medium composition for SCP production were systematically optimized using single-factor experiments and response surface methodology (RSM). Results showed that the optimal growth conditions were 28 °C, pH 7.0, and with 1 g/L (NH₄)₂SO₄ as the nitrogen source, 5–10% oxygen concentration, 9.70 mg/L FeSO₄·7H₂O, 0.17 g/L CaCl₂·2H₂O, and 1.90 mg/L MnSO₄·H₂O. Under the optimized conditions, strain ZZH C-3 achieved a maximum specific growth rate of 0.46 h⁻¹. After 28 h of cultivation, the optical density at 600 nm (OD₆₀₀) reached 0.94, corresponding to a biomass concentration of 0.60 g/L, and the protein content ranked at 73.56%. The biomass yield on hydrogen (Y_H2) was approximately 3.01 g/g H₂, with an average H₂-to-CO₂ consumption molar ratio of about 3.78. Compared to the model HOB Cupriavidus necator, strain ZZH C-3 exhibited a lower H₂/CO₂ consumption ratio, superior substrate conversion efficiency, and high protein content. Overall, this study not only validated the potential of mangrove HOB for SCP production but also offers new insights for future metabolic engineering strategies designed to enhance CO₂-to-biomass conversion efficiency.