Cultivation of Arthrospira platensis in Veterinary Hospital Wastewater Enhances Pigment Production and Reduces Antibiotic Resistance Genes

Veterinary hospital wastewater (VHW) is a significant environmental concern due to its high nutrient content, organic pollutants, and antibiotic resistance genes (ARGs). This study evaluated the physicochemical properties of VHW, its potential to support <i>Arthrospira platensis</i> cultivation, and its effects on microbial and resistome profiles. VHW contained high levels of ammonia nitrogen, total Kjeldahl nitrogen, biological oxygen demand (BOD), and chemical oxygen demand (COD), indicating substantial contamination. <i>A. platensis</i> was cultivated for 8 days in Zarrouk medium supplemented with 0-100% VHW. Biomass production peaked in 25% VHW (0.78 ± 0.05 g/L), while growth was strongly suppressed at concentrations ≥75%. Pigment levels in 25% VHW increased significantly compared to the control: 1.3-fold for chlorophyll-<i>a</i> (12.0 μg/mL), 1.5-fold for carotenoids (4.4 μg/mL), 1.7-fold for phycocyanin (120 μg/mL), and 2.3-fold for allophycocyanin (54 μg/mL). Shotgun metagenomic analysis revealed that <i>A. platensis</i> cultivation markedly altered the microbial community and reduced the prevalence of ARGs. In 25% VHW, Proteobacteria dominated the community (97.0%), but their abundance declined to 11.6% when co-cultivated with <i>A. platensis</i>. Likewise, <i>Acinetobacter</i> sp. carrying high levels of the <i>aph</i> gene, along with <i>Methylophaga</i> sp. and <i>Pseudomonas_E</i> sp. harboring <i>oqxB</i>, decreased substantially, suggesting that <i>A. platensis</i> effectively suppressed ARG-rich genera. These findings highlight the dual potential of <i>A. platensis</i> for sustainable pigment-rich biomass production and efficient wastewater treatment.