Publications

4364

Abstract Many insects engage in stable nutritional symbioses with bacteria that supplement limiting essential nutrients to their host. While several plant sap-feeding Hemipteran lineages are known to be simultaneously associated with two or more endosymbionts with complementary biosynthetic pathways to synthesize amino acids or vitamins, such co-obligate symbioses have not been functionally characterized in other insect orders. Here, we report on the characterization of a dual co-obligate, bacteriome-localized symbiosis in a family of xylophagous beetles using comparative genomics, fluorescence microscopy, and phylogenetic analyses. Across the beetle family Bostrichidae, most investigated species harbored the Bacteroidota symbiont Shikimatogenerans bostrichidophilus that encodes the shikimate pathway to produce tyrosine precursors in its severely reduced genome, likely supplementing the beetles’ cuticle biosynthesis, sclerotisation, and melanisation. One clade of Bostrichid beetles additionally housed the co-obligate symbiont Bostrichicola ureolyticus that is inferred to complement the function of Shikimatogenerans by recycling urea and provisioning the essential amino acid lysine, thereby providing additional benefits on nitrogen-poor diets. Both symbionts represent ancient associations within the Bostrichidae that have subsequently experienced genome erosion and co-speciation with their hosts. While Bostrichicola was repeatedly lost, Shikimatogenerans has been retained throughout the family and exhibits a perfect pattern of co-speciation. Our results reveal that co-obligate symbioses with complementary metabolic capabilities occur beyond the well-known sap-feeding Hemiptera and highlight the importance of symbiont-mediated cuticle supplementation and nitrogen recycling for herbivorous beetles.

Biological nitrogen fixation plays a crucial role in the marine nitrogen cycle, impacting global marine productivity and related carbon fluxes. The strains were analyzed by gene annotation, growth conditions and phylogenetic analysis of 16S rRNA gene sequences.These two strains were isolated from the coastal sediment at Xiaoshi Island in Weihai, China. The strains were analyzed by gene annotation, growth conditions and phylogenetic analysis of 16S rRNA gene sequences. It was revealed that strains D04T and AATT contain a set of nif gene clusters responsible for nitrogen fixation. Cell are yellow-colored, Gram-stain-negative, facultatively anaerobic, and rod-shaped bacteria. The optimal growth conditions for strain D04T were found to be at 33 °C, pH 7.0, and in 2% (w/v) NaCl, while strain AATT prefers growth conditions at 33 °C, pH 6.5, and in 3% (w/v) NaCl. The highest similarity of strains D04T and AATT was to Saccharicrinis fermentans NBRC 15936T, with a similarity of 94.1% and 94.8%, respectively. The 16S rRNA gene sequence similarity between the two strains was 96.6%. These novel strains were found to represent new taxa of the Marinilabiliaceae family, and we propose the names Plebeiobacterium marinum gen. nov., sp. nov. and Plebeiobacterium sediminum sp. nov. with type strains D04T (MCCC 1H00493T = KCTC 92026T) and AATT (MCCC 1H00485T = KCTC 92028T), respectively. In this study, nitrogen fixation genes were predicted for 53 strains from the whole order Marinilabiliales and it was found that nitrogen fixation gene clusters were present in 26 strains. These gene clusters were found in every family in the order, highlighting that the presence of nitrogen-fixing gene clusters in the order is common. Nitrogen-fixing bacteria in sediments play an important role in various biogeochemical cycles. Thus, understanding the oceanic nitrogen cycle can provide insights into the energy flow of marine systems.

Abstract In the ongoing debates about eukaryogenesis—the series of evolutionary events leading to the emergence of the eukaryotic cell from prokaryotic ancestors—members of the Asgard archaea play a key part as the closest archaeal relatives of eukaryotes 1 . However, the nature and phylogenetic identity of the last common ancestor of Asgard archaea and eukaryotes remain unresolved 2–4 . Here we analyse distinct phylogenetic marker datasets of an expanded genomic sampling of Asgard archaea and evaluate competing evolutionary scenarios using state-of-the-art phylogenomic approaches. We find that eukaryotes are placed, with high confidence, as a well-nested clade within Asgard archaea and as a sister lineage to Hodarchaeales, a newly proposed order within Heimdallarchaeia. Using sophisticated gene tree and species tree reconciliation approaches, we show that analogous to the evolution of eukaryotic genomes, genome evolution in Asgard archaea involved significantly more gene duplication and fewer gene loss events compared with other archaea. Finally, we infer that the last common ancestor of Asgard archaea was probably a thermophilic chemolithotroph and that the lineage from which eukaryotes evolved adapted to mesophilic conditions and acquired the genetic potential to support a heterotrophic lifestyle. Our work provides key insights into the prokaryote-to-eukaryote transition and a platform for better understanding the emergence of cellular complexity in eukaryotic cells.

Abstract Na.no.pu.sil'lus. Gr. masc. n. nânos, a dwarf; L. masc. adj. pusillus, very small; N.L. masc. n. Nanopusillus, a very small member of the Nanoarchaeota . The genus Candidatus Nanopusillus is comprised of small coccoid cells (∼100–400 nm) that live epibiotically on the surface of archaeal hosts. The first described species, Candidatus Nanopusillus acidilobi, is an anaerobic, hyperthermophilic acidophile whose best growth is observed at 82°C, pH 3.6, cultivated from a hot spring in Yellowstone National Park. Ca . Nanopusillus acidilobi cells associate with the Crenarchaeota host organism Acidilobus sp. 7A. Archaeal flagella (archaella) have been predicted from the genome sequence and shown to be expressed in the proteome. A second putative species, Candidatus Nanopusillus massiliensis, was recently reported from human dental plaque and associates with the methanogen Methanobrevibacter oralis . The genome consists of a single scaffold which is highly fragmented by spans of ambiguous nucleotides, with 16S rRNA gene fragments from Bacteria . Both species have small genomes (∼0.6 Mb) encoding few biosynthetic genes and no apparent ATP synthase complex genes, suggesting that the nanoarchaeotes rely on their host for the production of major cellular precursors. DNA G + C content (mol%) : 24 (genome analysis). Type species : Candidatus Nanopusillus acidilobi Wurch et al. 2016. Taxonomic and Nomenclature Notes According to the List of Prokaryotic names with Standing in Nomenclature (LPSN), the taxonomic status of the genus Candidatus Nanopusillus is: preferred name (not correct name) (last update, February 2025) * . LPSN classification: Archaea / Nanobdellati / Nanobdellota / Nanobdellia / Nanobdellales / Nanobdellaceae / Candidatus Nanopusillus The genus Candidatus Nanopusillus can also be recovered in the Genome Taxonomy Database (GTDB) as g__Nanopusillus (version v220) ** . GTDB classification: d__Archaea / p__Nanoarchaeota / c__Nanoarchaeia / o__Nanoarchaeales / f__Nanopusillaceae / g__Nanopusillus * Meier‐Kolthoff et al. ( 2022 ). Nucleic Acids Res , 50 , D801 – D807 ; DOI: 10.1093/nar/gkab902 ** Parks et al. ( 2022 ). Nucleic Acids Res , 50 , D785 – D794 ; DOI: 10.1093/nar/gkab776