Adaptation responses of Dunaliella sp. and its natural symbiotic bacteria to sulfamethoxazole

Microalgal-bacterial consortia provide a sustainable, low-cost solution for antibiotic-contaminated wastewater remediation. Microalgae cultivation typically involves natural symbiotic bacteria, which are often overlooked. To fill this gap, this study evaluated the adaptive response of Dunaliella sp. and its natural symbiotic bacteria to sulfamethoxazole (SMX) through cultivation experiments and 16S rDNA sequencing. The results demonstrated strong SMX tolerance but limited removal efficiency by the consortium. The adaptive responses were characterized by increased bacterial diversity and connectivity, with quorum sensing bacteria-driven community changes and biofilm formation playing a critical role in this process. Dunaliella sp. exhibited strong antioxidant capacity (with catalase playing a key role) and increased extracellular polymeric substances secretion, which not only contributed to its tolerance but also promoted microalgae-bacteria interactions, enhancing consortium adaptability. These findings strengthen our understanding of the responses of natural symbiotic bacteria to antibiotics and advance the development of microalgae-bacteria symbiosis technology for wastewater treatment. • The study first evaluated natural symbiotic bacteria toward sulfamethoxazole (SMX). • Diversity and connectivity of natural symbiotic bacteria increase under SMX. • Dunaliella sp. consortium showed high SMX tolerance but low removal efficiency. • Quorum sensing bacteria drove changes in community diversity and connectivity. • Strengthens the understanding of natural symbiotic bacteria to antibiotics.