High-Throughput Sequencing Analyzed the Effects of Three Antibiotics on the Bacterial Community in the Phycosphere of Typical Harmful Algae During Laboratory Culturing

The long-term laboratory preservation of algae serves as the foundation for research on harmful algal blooms (HABs). Purification by antibiotics during the preservation may inhibit algal growth and alter the phycosphere bacterial community. However, related research remains relatively rare. In this study, 16S rDNA V3-V4 region-based high-throughput sequencing was used to analyze the impact of three antibiotics (penicillin-streptomycin-amphotericin) on the algal-associated microbiome of three common HAB-forming species Akashiwo sanguinea, Karenia mikimotoi, and Alexandrium tamarense. Results showed that the antibiotics significantly inhibited the growth of A. sanguinea and A. tamarense. Although algal species exerted a primary effect on these bacterial communities, with antibiotics also exerting a significant impact. In antibiotic-treated A. sanguinea cultures, relative aboundance of Enterobacterales species like Alteromonas mediterranea were suppressed, whereas Pseudomonas stutzeri were elevated. Antibiotics also suppressed the growth of Yoonia vestfoldensis in the K. mikimotoi cultures and Dinoroseobacter shibae in A. tamarense cultures. Functional predictions based on 16S rDNA data showed that antibiotic addition significantly upregulated the expression of transport-related systems, such as ABC transporters associated with efflux pumps, while downregulating metabolism-related functions in algal-associated bacteria. Collectively, our results indicated that phycosphere bacterial communities primarily differed by algal species, followed by antibiotic addition; bacteria with broad-spectrum antibiotic resistance mechanisms, such as efflux pump, may benefit from antibiotic pressure; and algal-bacteria relations might be involved in growth inhibition of antibiotics.