Publications

3795

AbstractCyanobacterial mats supplanting coral and spreading coral diseases in tropical reefs, intensified by environmental shifts caused by human‐induced pressures, nutrient enrichment, and global climate change, pose grave risks to the survival of coral ecosystems. In this study, we characterized Okeanomitos corallinicola gen. and sp. nov., a newly discovered toxic marine heterocyte‐forming cyanobacterium isolated from a coral reef ecosystem of the South China Sea. Phylogenetic analysis, based on the 16S rRNA gene and the secondary structure of the 16S–23S rRNA intergenic region, placed this species in a clade distinct from closely related genera, that is, Sphaerospermopsis stricto sensu, Raphidiopsis, and Amphiheterocytum. The O. corallinicola is a marine benthic species lacking gas vesicles, distinguishing it from other members of the Aphanizomenonaceae family. The genome of O. corallinicola is large and exhibits diverse functional capabilities, potentially contributing to the resilience and adaptability of coral reef ecosystems. In vitro assays revealed that O. corallinicola demonstrates notable cytotoxic activity against various cancer cell lines, suggesting its potential as a source of novel anticancer compounds. Furthermore, the identification of residual saxitoxin biosynthesis function in the genome of O. corallinicola, a marine cyanobacteria, supports the theory that saxitoxin genes in cyanobacteria and dinoflagellates may have been horizontally transferred between them or may have originated from a shared ancestor. Overall, the identification and characterization of O. corallinicola provides valuable contributions to cyanobacterial taxonomy, offering novel perspectives on complex interactions within coral reef ecosystems.

AbstractNitrogen (N2) fixation in oligotrophic surface waters is the main source of new nitrogen to the ocean1 and has a key role in fuelling the biological carbon pump2. Oceanic N2 fixation has been attributed almost exclusively to cyanobacteria, even though genes encoding nitrogenase, the enzyme that fixes N2 into ammonia, are widespread among marine bacteria and archaea3–5. Little is known about these non-cyanobacterial N2 fixers, and direct proof that they can fix nitrogen in the ocean has so far been lacking. Here we report the discovery of a non-cyanobacterial N2-fixing symbiont, ‘Candidatus Tectiglobus diatomicola’, which provides its diatom host with fixed nitrogen in return for photosynthetic carbon. The N2-fixing symbiont belongs to the order Rhizobiales and its association with a unicellular diatom expands the known hosts for this order beyond the well-known N2-fixing rhizobia–legume symbioses on land6. Our results show that the rhizobia–diatom symbioses can contribute as much fixed nitrogen as can cyanobacterial N2 fixers in the tropical North Atlantic, and that they might be responsible for N2 fixation in the vast regions of the ocean in which cyanobacteria are too rare to account for the measured rates.

A Gram-stain-positive, rod-shaped, aerobic, motile bacterium, J379T, was isolated from radioactive water spring C1, located in a former silver–uranium mine in the Czech Republic. This slow-growing strain exhibited optimal growth at 24–28 °C on solid media with <1 % salt concentration and alkaline pH 8–10. The only respiratory quinone found in strain J379T was MK-7(H4). C18 : 1 ω9c (60.9 %), C18 : 0 (9.4 %), C16 : 0 and alcohol-C18 : 0 (both 6.2 %) were found to be the major fatty acids. The peptidoglycan contained directly cross-linked meso-diaminopimelic acid. Phylogenetic reconstruction based on the 16S rRNA gene sequences and the core-genome analysis revealed that strain J379T forms a separate phylogenetic lineage within the recently amended order Solirubrobacterales. A comparison of the 16S rRNA gene sequences between strain J379T and other members of the order Solirubrobacterales showed <96 % similarity. This analysis revealed that the closest type strains were Parviterribacter kavangonensis D16/0 /H6T (95.2 %), Capillimicrobium parvum 0166_1T (94.9 %) and Conexibacter arvalis KV-962T (94.5 %). Whole-genome analysis showed that the closest type strain was Baekduia soli BR7-21T with an average nucleotide identity of 78 %, average amino acid identity of 63.2 % and percentage of conserved proteins of 48.2 %. The G+C content of the J379T genomic DNA was 71.7 mol%. Based on the phylogenetic and phylogenomic data, as well as its physiological characteristics, strain J379T is proposed to represent a type strain (DSM 113746T=CCM 9300T) of Svornostia abyssi gen. nov. sp. nov. within the family Baekduiaceae.

Numerous bacteria in the human gut microbiome remains unknown and/or have yet to be cultured. While collections of human gut bacteria have been published, none are publicly accessible. This is partly due to issues with the deposition of strains to public culture collections. We address these key issues (microbial unknowns, lack of public access to isolates) by proposing a framework that facilitates large-scale submission of isolates, exemplified by a rich collection of human gut isolates that is taxonomically described, functionally novel, and made publicly available. An innovative bulk strain submission system was established by large-scale generation and curation of persistent strain identifiers (https://straininfo.dsmz.de). This was used to create the Human intestinal Bacterial Collection (www.hibc.rwth-aachen.de), which contains 340 strains representing 198 species within 29 families and 7 phyla, of which 32 previously unknown taxa are taxonomically described and named. These included three butyrate-producing species of Faecalibacterium and new dominant species associated with health and inflammatory bowel disease. Plasmids were identified to be prolific within the HiBC isolates, with almost half (46%) of strains containing one or more plasmids (up to 6). Megaplasmids were identified within two strains, one of them is globally present within multiple Bacteroidales species. The strain submission framework and public collection of easily searchable and available gut bacterial isolates presented here will facilitate the work of many by enabling functional studies.