Publications

4477

Abstract Background Tramway Ridge, a geothermal Antarctic Specially Protected Area (1) (elevation 3340 m) located near the summit of Mount Erebus, is home to a unique community composed of cosmopolitan surface-associated micro-organisms and abundant, poorly understood subsurface-associated microorganisms (2–5). Here, we use shotgun metagenomics to compare the functional capabilities of this community to those found elsewhere on Earth and to infer endemism and metabolic capabilities of abundant subsurface taxa. Results We found that the functional potential in this community is most similar to that found in terrestrial hydrothermal environments (hot springs, sediments) and that the two dominant organisms in the subsurface are primarily endemic. They were found to be facultative anaerobic heterotrophs that likely share a pool of nitrogenous organic compounds while specializing in different carbon compounds. Conclusions Metagenomic insights have provided a detailed understanding of the microbe-based ecosystem found in geothermally heated fumaroles at Tramway Ridge. This approach enabled us to compare Tramway Ridge with other microbial systems, identify endemic taxa and elucidate the key metabolic pathways that may enable specific organisms to dominate the ecosystem.

ABSTRACT The archaeal mevalonate pathway is a recently discovered modified version of the eukaryotic mevalonate pathway. This pathway is widely conserved in archaea, except for some archaeal lineages possessing the eukaryotic or other modified mevalonate pathways. Although the pathway seems almost exclusive to the domain Archaea, the whole set of homologous genes of the pathway is found in the metagenome-assembled genome sequence of an uncultivated bacterium, Candidatus Promineifilum breve, of the phylum Chloroflexota. To prove the existence of the archaea-specific pathway in the domain Bacteria, we confirmed the activities of the enzymes specific to the pathway, phosphomevalonate dehydratase and anhydromevalonate phosphate decarboxylase, because only these two enzymes are absent in closely related Chloroflexota bacteria that possess a different type of modified mevalonate pathway. The activity of anhydromevalonate phosphate decarboxylase was evaluated by carotenoid production via the archaeal mevalonate pathway reconstituted in Escherichia coli cells, whereas that of phosphomevalonate dehydratase was confirmed by an in vitro assay using the recombinant enzyme after purification and iron-sulfur cluster reconstruction. Phylogenetic analyses of some mevalonate pathway-related enzymes suggest an evolutionary route for the archaeal mevalonate pathway in Candidatus P. breve, which probably involves horizontal gene transfer events. IMPORTANCE The recent discovery of various modified mevalonate pathways in microorganisms, such as archaea and Chloroflexota bacteria, has shed light on the complexity of the evolution of metabolic pathways, including those involved in primary metabolism. The fact that the archaeal mevalonate pathway, which is almost exclusive to the domain Archaea, exists in a Chloroflexota bacterium provides valuable insights into the molecular evolution of the mevalonate pathways and associated enzymes. Putative genes probably involved in the archaeal mevalonate pathway have also been found in the metagenome-assembled genomes of Chloroflexota bacteria. Such genes can contribute to metabolic engineering for the bioproduction of valuable isoprenoids because the archaeal mevalonate pathway is known to be an energy-saving metabolic pathway that consumes less ATP than other mevalonate pathways do.

Coral reefs are marine biodiversity hotspots that provide a wide range of ecosystem services. They are also reservoirs of bioactive compounds, many of which are produced by microbial symbionts associated with reef invertebrate hosts. However, for the keystone species of coral reefs, the reef-building corals themselves, we still lack a systematic assessment of their microbially encoded biosynthetic potential, and thus the molecular resources that may be at stake due to the alarming decline in reef biodiversity and cover. Here, we analysed microbial genomes reconstructed from 820 reef-building coral samples of three representative coral genera collected at 99 reefs across 32 islands during a two-year expedition throughout the Pacific Ocean (Tara Pacific). By contextualising our analyses with the microbiomes of other reef species, we found that genomic information was previously available for only 10% of the 4,224 microbial species overall and for less than 1% of the 645 species exclusively identified in Tara Pacific samples. We found reef-building coral microbiomes to be host-specific and their biosynthetic potential to rival or even surpass that found in traditional targets for natural product discovery, such as sponges and soft corals. Fire corals were not only particularly diverse in microbially encoded biosynthetic gene clusters (BGCs), but also in BGC-rich bacteria, including Acidobacteriota spp., which have been recently highlighted for their promising natural product repertoire. Together, this study unveils new candidate sources for bioactive compound discovery, prioritises targets for microbial isolation, and underscores the importance of conservation efforts by linking macro-organismal biodiversity loss to host-specific microbiomes and their biotechnological potential.

Hadal zones account for the deepest 45% of the oceanic depth range and play an important role in ocean biogeochemical cycles. As the least-explored aquatic habitat on earth, hadal ecosystems contain a vast diversity of so far uncultured microorganisms that cannot be grown on conventional laboratory culture media. Therefore, it has been difficult to gain a true understanding of the detailed metabolic characteristics and ecological functions of those difficult-to-culture microorganisms in hadal environments. In this study, a novel anaerobic bacterial strain, MT110T, was isolated from a hadal sediment–water interface sample of the Mariana Trench at 10,890 m. The level of 16S rRNA gene sequence similarity and percentage of conserved proteins between strain MT110T and the closest relatives, Anaerovorax odorimutans DSM 5092T (94.9 and 46.6%) and Aminipila butyrica DSM 103574T (94.4 and 46.7%), indicated that strain MT110T exhibits sufficient molecular differences for genus-level delineation. Phylogenetic analyses based on both 16S rRNA gene and genome sequences showed that strain MT110T formed an independent monophyletic branch within the family Anaerovoracaceae. The combined evidence showed that strain MT110T represents a novel species of a novel genus, proposed as Anoxybacterium hadale gen. nov. sp. nov. (type strain MT110T = KCTC 15922T = MCCC 1K04061T), which represents a previously uncultured lineage of the class Clostridia. Physiologically, no tested organic matter could be used as sole carbon source by strain MT110T. Genomic analysis showed that MT110T had the potential capacity of utilizing various carbon sources, but the pathways of sulfur reduction were largely incomplete. Our experiments further revealed that cysteine is one of the essential nutrients for the survival of strain MT110T, and cannot be replaced by sulfite, leucine, or taurine. This result suggests that organic sulfur compounds might play an important role in metabolism and growth of the family Anaerovoracaceae and could be one of the key factors affecting the cultivation of the uncultured microbes. Our study brings a new perspective to the role of dissolved organic sulfur in hadal ecosystems and also provides valuable information for optimizing the conditions of isolating related microbial taxa from the hadal environment.

ABSTRACT The microbial communities of marine seep sediments contain unexplored physiological and phylogenetic diversity. Here, we examined 30 bacterial metagenome-assembled genomes (MAGs) from cold seeps in the South China Sea, the Indian Ocean, the Scotian Basin, and the Gulf of Mexico, as well as from deep-sea hydrothermal sediments in the Guaymas Basin, Gulf of California. Phylogenetic analyses of these MAGs indicate that they form a distinct phylum-level bacterial lineage, which we propose as a new phylum, Candidatus Effluviviacota, in reference to its preferential occurrence at diverse seep areas. Based on tightly clustered high-quality MAGs, we propose two new genus-level candidatus taxa, Candidatus Effluvivivax and Candidatus Effluvibates. Genomic content analyses indicate that Candidatus Effluviviacota are chemoheterotrophs that harbor the Embden–Meyerhof–Parnas glycolysis pathway. They gain energy by fermenting organic substrates. Additionally, they display potential capabilities for the degradation of cellulose, hemicellulose, starch, xylan, and various peptides. Extracellular anaerobic respiration appears to rely on metals as electron acceptors, with electron transfer primarily mediated by multiheme cytochromes and by a flavin-based extracellular electron transfer (EET) mechanism that involves NADH-quinone oxidoreductase-demethylmenaquinone-synthesizing enzymes, uncharacterized membrane proteins, and flavin-binding proteins, also known as the NUO-DMK-EET-FMN complex. The heterogeneity within the Ca . Effluviviacota phylum suggests varying roles in energy metabolism among different genera. While NUO-DMK-EET-FMN electron transfer has been reported predominantly in Gram-positive bacteria, it is now identified in Ca . Effluviviacota as well. We detected the presence of genes associated with bacterial microcompartments in Ca . Effluviviacota, which can promote specific metabolic processes and protect the cytosol from toxic intermediates. IMPORTANCE The newly discovered bacterial phylum Candidatus Effluviviacota is widespread across diverse seepage ecosystems, marine environments, and freshwater environments, with a notable preference for cold seeps. While maintaining an average abundance of approximately 1% in the global gene catalog of cold seep habitats, it has not hitherto been characterized. The metabolic versatility of Ca . Effluviviacota in anaerobic carbon, hydrogen, and metal cycling aligns with its prevalence in anoxic niches, with a preference for cold seep environments. Variations in metabolic potential between Ca . Effluvivivax and Ca . Effluvibates may contribute to shaping their respective habitat distributions.

ABSTRACT The Chichon volcano contains several thermal manifestations including an acidic crater lake. Here we report a metagenome-assembled genome of “ Candidatus Aramenus sp. CH1,” a Sulfolobales archaeon inhabiting the crater lake from the Chichon volcano. In this study, we generated a novel Aramenus genome sequence from a thermal area in Southern Mexico.

Debido a la rápida diseminación de la enfermedad más devastadora de los cítricos a nivel mundial conocida como Huanglongbing (HLB), es necesario desarrollar tecnologías alternativas para su diagnóstico oportuno. En este trabajo se realizó la predicción de epítopos en la proteína DR-7, localizada en la membrana externa de la bacteria Candidatus Liberibacter asiaticus que afecta al limón Mexicano, la cual fue caracterizada con capacidad antigénica. Mediante el uso de la base de datos IEDB Analysis Resource y utilizando los métodos Bepipred Predicción de Epítopos Lineales y Escala de antigenicidad de Kolaskar y Tongaonkar epítopos, se identificaron 24 epítopos en la proteína. Con la base de datos Inmune Epitope and Analysis Resource se seleccionaron siete de estos epítopos validados experimentalmente. Además, la proteína DR-7, presentó un 91% de antigenicidad en la Escala de Kolaskar y Tongaonkar, lo cual la constituye como un excelente candidato para el desarrollo de un método de diagnóstico temprano del HLB.

The high diversity and global distribution of heterotrophic bacterial diazotrophs (HBDs) in the ocean has recently become apparent. However, understanding the role these largely uncultured microorganisms play in marine N 2 fixation poses a challenge due to their undefined growth requirements and the complex regulation of the nitrogenase enzyme. We isolated and characterized Candidatus Thalassolituus haligoni, a member of a widely distributed clade of HBD belonging to the Oceanospirillales. Analysis of its nifH gene via amplicon sequencing revealed the extensive distribution of Cand. T. haligoni across the Pacific, Atlantic, and Arctic Oceans. Pangenome analysis indicates that the isolate shares >99% identity with an uncultured metagenome-assembled genome called Arc-Gamma-03, recently recovered from the Arctic Ocean. Through combined genomic, proteomic, and physiological approaches, we confirmed that the isolate fixes N 2 gas. However, the mechanisms governing nitrogenase regulation in Cand. T. haligoni remain unclear. We propose Cand. T. haligoni as a globally distributed, cultured HBD model species within this understudied clade of Oceanospirillales.

AbstractThis study is the first to investigate the presence and movement of the novel Liberibacter species ‘Candidatus Liberibacter brunswickensis’ (CLbr) in eggplant, Solanum melongena. The psyllid, Acizzia solanicola can transmit CLbr to eggplant and CLbr can be acquired by CLbr-negative A. solanicola individuals from CLbr-positive eggplants. In planta, CLbr can replicate, move and persist. Investigation into the early development of eggplants showed that CLbr titres had increased at the inoculation site at 14 days post inoculation access period (DPIAP). CLbr had become systemic in the majority of plants tested by 28 DPIAP. The highest bacterial titres were recorded at 35 DPIAP in all samples of the inoculated leaf, the roots, stems and the midrib and petiole samples of the newest leaf (the top leaf). This finding strongly suggests that CLbr movement in planta follows the source to sink relationship as previously described for ‘Ca. Liberibacter asiaticus’ (CLas) and ‘Ca. Liberibacter solanacearum’ (CLso). No symptoms consistent with Liberibacter-associated diseases were noted for plants colonised by CLbr during this study, consistent with the hypothesis that CLbr does not cause disease of eggplant during the early stages of host colonisation. In addition, no significant differences in biomass were found between eggplant colonised with CLbr, compared to those that were exposed to CLbr-negative A. solanicola, and to control plants.