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 Arthrospira platensis 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. A. platensis 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-a (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 A. platensis 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 A. platensis. Likewise, Acinetobacter sp. carrying high levels of the aph gene, along with Methylophaga sp. and Pseudomonas_E sp. harboring oqxB, decreased substantially, suggesting that A. platensis effectively suppressed ARG-rich genera. These findings highlight the dual potential of A. platensis for sustainable pigment-rich biomass production and efficient wastewater treatment.

Microplastics (MPs), particularly low-density polyethylene (LDPE), are widespread pollutants in aquatic environments and may affect cyanobacterial physiology. This study investigated the concentration-dependent effects of LDPE-MPs on the physiology and transcriptomic responses of Arthrospira platensis. Cultures were exposed to 10–5000 mg/L LDPE-MPs (nominal size ≤ 500 µm) for 16 days. Low to moderate concentrations (10–1000 mg/L) produced minimal effects on growth, biomass accumulation, or pigment contents. In contrast, higher concentrations (3000–5000 mg/L) were associated with reduced growth and biomass, accompanied by declines in chlorophyll a (Chl a) and phycobiliproteins over time. By day 16 at 5000 mg/L, biomass and Chl a decreased to 1.47 ± 0.03 g/L and 8.39 ± 0.24 µg/mL, respectively, compared with 1.64 ± 0.04 g/L and 10.81 ± 0.52 µg/mL in the control (p < 0.05). Accordingly, Chl a yield decreased by 13%. Field-emission scanning electron microscopy revealed adhesion of LDPE particles to filament surfaces and the formation of extracellular polymeric substance (EPS)-rich aggregates, which may influence light availability and nutrient exchange. Transcriptomic analysis indicated changes in several metabolic pathways, including nitrogen assimilation, photosynthetic electron transport, carbon metabolism, and metal homeostasis, together with differential expression of genes related to stress responses and EPS biosynthesis. Overall, these findings suggest that relatively high concentrations of LDPE microplastics may influence physiological and metabolic processes in A. platensis.

Swine wastewater is a nutrient-rich waste stream with considerable potential for cyanobacterial cultivation and resource recovery. However, its impacts on microbial community dynamics and antibiotic resistance genes (ARGs) remain poorly understood. This study evaluated the cultivation of Arthrospira platensis in a medium containing 25% swine wastewater and 75% Zarrouk medium (SWW₂₅) using a flat-panel photobioreactor. A. platensis achieved a biomass concentration of 1.58 ± 0.02 g/L, a biomass productivity of 0.11 ± 0.01 g/L/d, and a specific growth rate of 0.26 ± 0.01 d⁻¹. Simultaneously, the system removed 98.5% of ammonium nitrogen and 80% of orthophosphate. Metagenomic analysis indicated changes in bacterial community composition during A. platensis cultivation. Microbial community analysis revealed shifts in relative abundance after cultivation, likely associated with changes in community composition following Arthrospira biomass enrichment, while Proteobacteria, Firmicutes, and Synergistota remained among the dominant phyla. In addition, ARG profiling indicated a decline in ARG diversity and read counts during cultivation, whereas tet(X) remained the only detectable ARG after A. platensis cultivation. Collectively, these findings suggest that A. platensis cultivation under non-axenic conditions was associated with biomass production, nutrient removal, and changes in microbial community composition and ARG profiles in swine wastewater.