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PubMed2026

Lithosyntrophy: Obligate syntrophy in a phosphite-oxidizing, methanogenic culture.

The anaerobic conversion of organic matter to methane and carbon dioxide typically relies on obligate syntrophic interactions between bacteria and methanogenic archaea, where interspecies electron transfer enables thermodynamically constrained reactions to proceed near equilibrium. Syntrophs often couple the oxidation of fermentation products such as fatty acids and alcohols to the reduction of protons to form hydrogen (H2). These reactions can only proceed if low H2 concentrations are maintained by H2-consuming syntrophic partners. Here, we describe "lithosyntrophy," a mode of syntrophic interaction in which electrons that drive hydrogenotrophic methanogenesis originate from an inorganic compound rather than from the canonical organic substrates. Candidatus Phosphitivorax anaerolimi Phox-21 oxidizes phosphite (HPO32-, oxidation state +3) to phosphate coupled to hydrogenogenesis in an obligate energetic dependency on a hydrogenotrophic methanogen, Methanoculleus sp. Physiology experiments, thermodynamic calculations, genomic annotation, and metaproteomics analysis collectively revealed a mechanism for syntrophic phosphite oxidation in Phox-21. In this pathway, electrons derived from phosphite drive H2 production via an electron-confurcating hydrogenase. Unlike previously characterized acetogenic phosphite oxidizers, Phox-21 is a mixotroph that assimilates acetate to form biomass. Lithosyntrophic phosphite oxidizers may play important roles both in transferring reducing equivalents as well as biologically available phosphorus to other members of their surrounding microbial communities, establishing a previously unrecognized metabolic and biogeochemical link between the phosphorus and carbon redox cycles in anoxic ecosystems.

Oxidation-Reduction↗

PubMed2025

Anaerobic breviate protist survival in microcosms depends on microbiome metabolic function.

Anoxic and hypoxic environments serve as habitats for diverse microorganisms, including unicellular eukaryotes (protists) and prokaryotes. To thrive in low-oxygen environments, protists and prokaryotes often establish specialized metabolic cross-feeding associations, such as syntrophy, with other microorganisms. Previous studies show that the breviate protist Lenisia limosa engages in a mutualistic association with a denitrifying Arcobacter bacterium based on hydrogen exchange. Here, we investigate if the ability to form metabolic interactions is conserved in other breviates by studying five diverse breviate microcosms and their associated bacteria. We show that five laboratory microcosms of marine breviates live with multiple hydrogen-consuming prokaryotes that are predicted to have different preferences for terminal electron acceptors using genome-resolved metagenomics. Protist growth rates vary in response to electron acceptors depending on the make-up of the prokaryotic community. We find that the metabolic capabilities of the bacteria and not their taxonomic affiliations determine protist growth and survival and present new potential protist-interacting bacteria from the Arcobacteraceae, Desulfovibrionaceae, and Terasakiella lineages. This investigation uncovers potential nitrogen and sulfur cycling pathways within these bacterial populations, hinting at their roles in syntrophic interactions with the protists via hydrogen exchange.

Anaerobiosis↗

PubMed2025

Phylogenomic Analyses Reveal that Panguiarchaeum Is a Clade of Genome-Reduced Asgard Archaea Within the Njordarchaeia.

The Asgard archaea are a diverse archaeal phylum important for our understanding of cellular evolution because they include the lineage that gave rise to eukaryotes. Recent phylogenomic work has focused on characterizing the diversity of Asgard archaea in an effort to identify the closest extant relatives of eukaryotes. However, resolving archaeal phylogeny is challenging, and the positions of 2 recently described lineages-Njordarchaeales and Panguiarchaeales-are uncertain, in ways that directly bear on hypotheses of early evolution. In initial phylogenetic analyses, these lineages branched either with Asgards or with the distantly related Korarchaeota, and it has been suggested that their genomes may be affected by metagenomic contamination. Resolving this debate is important because these clades include genome-reduced lineages that may help inform our understanding of the evolution of symbiosis within Asgard archaea. Here, we performed phylogenetic analyses revealing that the Njordarchaeales and Panguiarchaeales constitute the new class Njordarchaeia within Asgard archaea. We found no evidence of metagenomic contamination affecting phylogenetic analyses. Njordarchaeia exhibit hallmarks of adaptations to (hyper-)thermophilic lifestyles, including biased sequence compositions that can induce phylogenetic artifacts unless adequately modeled. Panguiarchaeum is metabolically distinct from its relatives, with reduced metabolic potential and various auxotrophies. Phylogenetic reconciliation recovers a complex common ancestor of Asgard archaea that encoded the Wood-Ljungdahl pathway. The subsequent loss of this pathway during the reductive evolution of Panguiarchaeum may have been associated with the switch to a symbiotic lifestyle, potentially based on H2-syntrophy. Thus, Panguiarchaeum may contain the first obligate symbionts within Asgard archaea besides the lineage leading to eukaryotes.

Phylogeny↗

PubMed1979

[Histomorphological liver changes due to extrahepatic biliary stresia].

Among 137 non-selected liver tissue specimens of 101 infants between 1968 and 1978 six cases of extrahepatic biliary atresia were found. For the pathologist examining the liver cylinder the differential diagnosis between biliary atresia and neonatal hepatitis may be extemely difficult. Findings typical of extrahepatic biliary atresia, such as obstruction of portal tracts, cannot be observed before the 4th or 6th week. Formerly, biliary atresia was considered as a congenital deformity. However, under morphologic aspects a positive syntrophy or a causative relationship between neonatal hepatitis and biliary atresia can at present not be excluded.

Bile Ducts↗

PubMed2026

Phylogenomics of Desulfuromonadia supports reclassification of Geobacter psychrophilus as Irobacter psychrophilus comb. nov. and proposal of Geosyntrophus gen. nov.

Genome-resolved phylogenomics reveals widespread misclassification of metal-reducing bacteria historically assigned to Geobacter based on 16S rRNA gene phylogeny, and highlights species that persist only as 16S rRNA entries without genomes for robust taxonomic resolution. Here, we resolve two such lineages by integrating whole-genome phylogeny with average amino acid identity (AAI) and percentage of conserved proteins (POCP) across 418 dereplicated genomes of Desulfuromonadia. We report a draft genome of the psychrophilic iron-reducing bacterium Geobacter psychrophilus (100% completeness). Phylogenomic analyses place both Geobacter psychrophilus and the GTDB placeholder genus g__JACRCG01 within the family 'Pseudopelobacteraceae', outside Geobacteraceae sensu stricto. Within this framework, G. psychrophilus forms a distinct, well-supported lineage separated from neighbouring genera by discontinuities in AAI and POCP, supporting its reclassification as Irobacter psychrophilus comb. nov. Additionally, we show that Geosyntrophus acetoxidans, a non-axenic syntrophic bacterium, forms a coherent genus with 51 other environmental genomes (placeholder genus g__JACRCG01), for which we propose the replacement name Geosyntrophus gen. nov. Comparative genome analysis revealed conserved family-level metabolic traits together with genus-specific differences in respiratory metabolism, while ANI-based clustering identified substantial species-level diversity within both proposed genera. Metagenome and 16S rRNA-gene survey data further show that Geosyntrophus and Irobacter occur in broadly similar aquatic and subsurface habitats spanning from the Arctic to the Antarctic. Together, these results resolve the taxonomy of two previously ambiguous Desulfuromonadales lineages and shed light on their environmental distribution.

AAI↗