ORIGINAL ABSTRACT

The green macroalga Ulva demonstrates exceptional growth rates, robustness, adaptability and potential for nitrogen and phosphorus removal; thus, it is a promising candidate for wastewater treatment and bioremediation. However, micropollutants in wastewater pose a potential threat to the holobiont. We explored the effects of emerging contaminants found in groundwater and wastewater on the microbiome of the cultivar Ulva compressa (conspecific with Ulva mutabilis). We identified the core microbiome by comparing the microbiome of the long-term cultivar (cultivated under laboratory conditions for over 70 years) with the native microbiome of U. compressa. Long-term cultivation was found to homogenise and reduce microbiome diversity; however, key functional taxa, including algal growth and morphogenesis-promoting bacteria, persisted. We subsequently challenged the core microbiome of the U. compressa cultivar with four antibiotics (chloramphenicol, erythromycin, oxytetracycline and sulfamethoxazole), two herbicides (atrazine, glyphosate) and three endocrine disruptors (bisphenol A, estradiol and ethinylestradiol). The micropollutants exerted distinct impacts, with antibiotics showing stronger effects than hormonal disruptors, which Ulva rapidly removes from the culture medium. In contrast, the microbiome did not contribute to the removal of these substances. These results indicate that although Ulva's microbiome is sensitive to environmental change, key functions with positive implications for aquaculture and ecosystem management are retained.