Sphingorhabdus lacus sp. nov. and Sphingorhabdus profundilacus sp. nov., isolated from freshwater environments.

Two Gram-stain-negative, aerobic, non-motile bacteria, designated IMCC1753T and IMCC26285T, were isolated from a shallow eutrophic pond and a deep oligotrophic lake, respectively. Results of 16S rRNA gene sequence analysis indicated that the two strains shared 99.8 % sequence similarity and were most closely related to Sphingorhabdus contaminans JC216T(98.7-98.8 %). The whole genome sequences of strains IMCC1753T and IMCC26285T were 3.5 and 2.9 Mbp in size with 56.6 and 55.5 mol% DNA G+C content, respectively. Average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values between the two strains were 82.2 and 25.8 %, respectively, indicating that they are separate species. The two strains showed ≤98.8 % 16S rRNA gene sequence similarities and ≤82.2 % ANI and ≤28.7 % dDDH values to closely related species of the genus Sphingorhabdus, indicating that the two strains each represent novel species. Major fatty acid constituents of strain IMCC1753T were C17 : 1 ω6c, C17 : 1 ω8c and summed features 3 (C16 : 1 ω6c and/or C16 : 1 ω7c) and 8 (C18 : 1 ω6c and/or C18 : 1 ω7c); those of strain IMCC26285T were summed features 3 and 8. The predominant isoprenoid quinone detected in both strains was ubiquinone-10 and the most abundant polyamine was spermidine. Both strains contained phosphatidylethanolamine, phosphatidylmethylethanolamine, phosphatidylcholine, phosphatidylglycerol, diphosphatidylglycerol and sphingoglycolipid as major polar lipids. On the basis of the phylogenetic and phenotypic characteristics, strains IMCC1753T and IMCC26285T were considered to represent two distinct novel species in the genus Sphingorhabdus, for which the names Sphingorhabdus lacus (IMCC1753T=KCTC 52480T=KACC 18985T=NBRC 112442T) and Sphingorhabdus profundilacus (IMCC26285T=KCTC 52479T=KACC 18986T=NBRC 112454T) are proposed, respectively.

Metagenome sequencing and recovery of 444 metagenome-assembled genomes from the biofloc aquaculture system.

Biofloc technology is increasingly recognised as a sustainable aquaculture method. In this technique, bioflocs are generated as microbial aggregates that play pivotal roles in assimilating toxic nitrogenous substances, thereby ensuring high water quality. Despite the crucial roles of the floc-associated bacterial (FAB) community in pathogen control and animal health, earlier microbiota studies have primarily relied on the metataxonomic approaches. Here, we employed shotgun sequencing on eight biofloc metagenomes from a commercial aquaculture system. This resulted in the generation of 106.6 Gbp, and the reconstruction of 444 metagenome-assembled genomes (MAGs). Among the recovered MAGs, 230 were high-quality (≥90% completeness, ≤5% contamination), and 214 were medium-quality (≥50% completeness, ≤10% contamination). Phylogenetic analysis unveiled Rhodobacteraceae as dominant members of the FAB community. The reported metagenomes and MAGs are crucial for elucidating the roles of diverse microorganisms and their functional genes in key processes such as nitrification, denitrification, and remineralization. This study will contribute to scientific understanding of phylogenetic diversity and metabolic capabilities of microbial taxa in aquaculture environments.