A Photosynthetic Bacterium Suitable for Treating High-Salinity Sea Cucumber Boiling Broth

Photosynthetic bacteria exhibit significant bioremediation potential and resource recycling characteristics, rendering them valuable candidates for sustainable wastewater treatment applications. Sea cucumber boiling broth (SCBB) contains high concentrations of organic compounds and nutrient salts, whose indiscriminate discharge poses serious environmental risks. This study aimed to evaluate a photosynthetic bacterium capable of effectively treating SCBB, which was isolated from the intertidal sediment samples. The bacterial strain was identified using 16S rDNA sequencing, and optimal growth conditions, including light, pH, and temperature, were determined. Finally, a small-scale trial was conducted in a fed-batch fermenter. The results showed that 16S rDNA analysis placed this strain in the Chromatiaceae family, forming a distinct lineage from the closest related species Marichromatium purpuratum and M. gracile, and was tentatively named Marichromatium sp. DYYC01. The strain exhibited optimal growth under anaerobic conditions at 30 °C, light intensity of 100 μmol photons/m2/s, and pH 7.0. Batch culture experiments demonstrated maximum biomass accumulation (OD660 = 0.831) in SCBB medium with an initial COD loading of 3913 mg L⁻1, concomitant with significant nutrient removal efficiencies: 76.45% COD, 55.82% total nitrogen (TN), and 56.67% total phosphorus (TP). Scaling up to fed-batch fermentation enhanced bioremediation performance, achieving removal rates of 83.13% COD, 72.17% TN, and 73.07% TP with enhanced growth (OD660 = 1.2). This study reveals Marichromatium sp. DYYC01’s exceptional halotolerance in high-salinity organic wastewater treatment. The strain’s capacity for simultaneous biomass production and efficient nutrient recovery from hypersaline processing effluent positions it as a promising candidate for developing circular bioeconomy strategies.