As a unique geographical transition zone, the estuary is considered as a model environment to decipher the diversity, functions and ecological processes of microbial communities, which play important roles in the global biogeochemical cycle. Here we used surface water metagenomic sequencing datasets to construct metagenome-assembled genomes (MAGs) from 30 subtropical estuaries at a large scale along South China. In total, 500 dereplicated MAGs with completeness ≥ 50% and contamination ≤ 10% were obtained, among which more than one-thirds (n = 207 MAGs) have a completeness ≥ 70%. These MAGs are dominated by taxa assigned to the phylum Proteobacteria (n = 182 MAGs), Bacteroidota (n = 110) and Actinobacteriota (n = 104). These draft genomes can be used to study the diversity, phylogenetic history and metabolic potential of microbiota in the estuary, which should help improve our understanding of the structure and function of these microorganisms and how they evolved and adapted to extreme conditions in the estuarine ecosystem.

Bactericidal/permeability-increasing protein (BPI) and lipopolysaccharide-binding protein (LBP) are a group of antibacterial proteins that play an important role in the host’s innate immune defense against pathogen infection. In this study, two BPI/LBPs, named ToBPI1/LBP (1434 bp in length, 478 amino acids) and ToBPI2/LBP (1422 bp in length, 474 amino acids), were identified from the golden pompano. ToBPI1/LBP and ToBPI2/LBP were significantly expressed in immune-related tissues after being challenged with Streptococcus agalactiae and Vibrio alginolyticus. The two BPI/LBPs showed significant antibacterial activity against Gram-negative Escherichia coli and Gram-positive S. agalactiae and Streptococcus iniae. In contrast, the antibacterial activity against Staphylococcus aureus, Corynebacterium glutamicum, Vibrio parahaemolyticus, V. alginolyticus and Vibrio harveyi was low and decreased with time. The membrane permeability of bacteria treated with recombinant ToBPI1/LBP and ToBPI2/LBP was significantly enhanced. These results suggest that ToBPI1/LBP and ToBPI2/LBP may play important immunological roles in the immune response of the golden pompano to bacteria. This study will provide basic information and new insights into the immune response mechanism of the golden pompano to bacteria and the function of BPI/LBP.