Biosynthetic potential of uncultured Antarctic soil bacteria revealed through long-read metagenomic sequencing

Microbial secondary metabolites: advancements to accelerate discovery towards application

Microbial secondary metabolites not only have key roles in microbial processes and relationships but are also valued in various sectors of today's economy, especially in human health and agriculture. The advent of genome sequencing has revealed a previously untapped reservoir of biosynthetic capacity for secondary metabolites indicating that there are new biochemistries, roles and applications of these molecules to be discovered. New predictive tools for biosynthetic gene clusters (BGCs) and their associated pathways have provided insights into this new diversity. Advanced molecular and synthetic biology tools and workflows including cell-based and cell-free expression facilitate the study of previously uncharacterized BGCs, accelerating the discovery of new metabolites and broadening our understanding of biosynthetic enzymology and the regulation of BGCs. These are complemented by new developments in metabolite detection and identification technologies, all of which are important for unlocking new chemistries that are encoded by BGCs. This renaissance of secondary metabolite research and development is catalysing toolbox development to power the bioeconomy.

"Genome-based in silico assessment of biosynthetic gene clusters in Planctomycetota: Evidences of its wide divergent nature"

The biotechnological potential of Planctomycetota only recently started to be unveiled. 129 reference genomes and 5194 available genomes (4988 metagenome-assembled genomes (MAGs)) were analysed regarding the presence of Biosynthetic Gene Clusters (BGCs). By antiSMASH, 987 BGCs in the reference genomes and 22,841 BGCs in all the available genomes were detected. The classes Ca Uabimicrobiia, Ca Brocadiia and Planctomycetia had the higher number of BGC per genome, while Phycisphaerae had the lowest number. The most prevalent BGCs found in Planctomycetota reference genomes were terpenes, NRPS, type III PKS, type I PKS. As much as 88 % of the predicted regions had no similarity with known clusters in MIBiG database. This study strengthens the uniqueness of Planctomycetota for the isolation of new compounds and provide an overview of BGCs taxonomic distribution and of the type of predicted product. This outline allows the acceleration and focus of the research on drug discovery in Planctomycetota.

Beyond correlation: Understanding the causal link between microbiome and plant health

Understanding the causal link between the microbiome and plant health is crucial for the future of crop production. Established studies have shown a symbiotic relationship between microbes and plants, reshaping our knowledge of plant microbiomes' role in health and disease. Addressing confounding factors in microbiome study is essential, as standardization enables precise identification of microbiome features that influence outcomes. The microbiome significantly impacts plant development, necessitating holistic investigation for maintaining plant health. Mechanistic studies have deepened our understanding of microbiome structure and function related to plant health, though much research still needs to be carried out. This review, therefore, discusses current challenges and proposes advancing studies from correlation to causation and translation. We explore current knowledge on the microbiome and plant health, emphasizing multi-omics approaches and hypothesis-driven research. Future studies should focus on developing translational research for producing probiotics and prebiotics from biomarkers that regulate the microbiome-plant health connection, promoting sustainable crop production through microbiome applications.

Bacterial community and antibiotic resistance genes assembly processes were shaped by different mechanisms in the deep-sea basins of the Western Pacific Ocean

As the intrinsic property of microorganisms, antibiotic resistance genes (ARGs) are fundamentally coupled to microbially-linked biogeochemical processes within ecosystems. However, human activities often obscure the natural distribution of ARGs through deterministic selective pressures. The deep-sea basin of the western Pacific Ocean is one of the least disturbed areas globally by human activities, providing a natural laboratory to investigate the intrinsic mechanisms governing ARGs in natural environments. In this study, we analyzed bacterial community and ARG diversity in 15 surface sediment samples from three deep-sea basins in the western Pacific Ocean. The relative abundance of ARGs in the surface sediments ranged from 3.10 × 10-3 to 5.37 × 10-2 copies/16S rRNA copies, with multidrug and β-lactam resistance genes dominated in all samples (49.06%-100%). The bacteria were mainly dominated by the Proteobacteria. The principal coordinate analysis (PCoA) showed significant spatial heterogeneity of ARGs and bacteria among the three basins. Null model, neutral community models (NCM), and normalized stochasticity ratio (NST) indicated that bacterial community was dominated by stochastic assembly, driven by geographic barriers leading to independent evolution. Conversely, the NST revealed that the ARGs profile was mainly shaped by deterministic processes. Environmental factors are more crucial than geographical factors and bacterial community for ARG occurrence among the selected factors. Meanwhile, we found that the spread of ARGs was mainly through vertical gene transfer in the pre-antibiotic era. The disparity between the assembly processes of bacterial community and ARGs may be attributed to the fact that ARG hosts were not the dominant bacteria in the community. This study first reported the distribution and assembly processes of ARGs and bacterial community in surface sediments of the western Pacific.

Mitigating risks from atrazine drift to soybeans through foliar pre-spraying with a degrading bacterium

Herbicides play a crucial role in managing weeds in agriculture, ensuring the productivity and quality of crops. However, herbicide drift poses a significant threat to sensitive plants, necessitating the consideration of ecosystem-based solutions to address this issue. In this study, foliar pre-spraying of atrazine-degrading Paenarthrobacter sp. AT5 was proposed as a new approach to mitigate the risks associated with atrazine drift on soybeans. Exposure to atrazine reduced chlorophyll levels and disturbed the antioxidant system and metabolic processes in soybean leaves, ultimately causing leaves to turn yellow. However, by pre-spraying, strain AT5 successfully colonized the surface of soybean leaves and mitigated the harmful effects of atrazine. This was achieved by slowing down atrazine absorption, expediting its reduction (half-life decreased from 2.22 d to 0.86 d), altering its degradation pathway (enhancing hydroxylation while weakening alkylation), and enhancing the interaction within phyllosphere bacteria communities. This study introduces a new approach that is both eco-friendly and user-friendly for reducing the risks of herbicide drift to sensitive crops, hence promoting the development of mixed cropping.

Long-read sequencing sheds light on key bacteria contributing to deadwood decomposition processes

BACKGROUND

Deadwood decomposition is an essential ecological process in forest ecosystems, playing a key role in nutrient cycling and carbon sequestration by enriching soils with organic matter. This process is driven by diverse microbial communities encompassing specialized functions in breaking down organic matter, but the specific roles of individual microorganisms in this process are still not fully understood.

RESULTS

Here, we characterized the deadwood microbiome in a natural mixed temperate forest in Central Europe using PacBio HiFi long-read sequencing and a genome-resolved transcriptomics approach in order to uncover key microbial contributors to wood decomposition. We obtained high quality assemblies, which allowed attribution of complex microbial functions such as nitrogen fixation to individual microbial taxa and enabled the recovery of metagenome-assembled genomes (MAGs) from both abundant and rare deadwood bacteria. We successfully assembled 69 MAGs (including 14 high-quality and 7 single-contig genomes) from 4 samples, representing most of the abundant bacterial phyla in deadwood. The MAGs exhibited a rich diversity of carbohydrate-active enzymes (CAZymes), with Myxococcota encoding the highest number of CAZymes and the full complement of enzymes required for cellulose decomposition. For the first time we observed active nitrogen fixation by Steroidobacteraceae, as well as hemicellulose degradation and chitin recycling by Patescibacteria. Furthermore, PacBio HiFi sequencing identified over 1000 biosynthetic gene clusters, highlighting a vast potential for secondary metabolite production in deadwood, particularly in Pseudomonadota and Myxococcota.

CONCLUSIONS

PacBio HiFi long-read sequencing offers comprehensive insights into deadwood decomposition processes by advancing the identification of functional features involving multiple genes. It represents a robust tool for unraveling novel microbial genomes in complex ecosystems and allows the identification of key microorganisms contributing to deadwood decomposition.

A widespread family of ribosomal peptide metallophores involved in bacterial adaptation to metal stress

Ribosomally synthesized and posttranslationally modified peptides (RiPPs) are a structurally diverse group of natural products that bacteria employ in their survival strategies. Herein, we characterized the structure, the biosynthetic pathway, and the mode of action of a RiPP family called bufferins. With thousands of homologous biosynthetic gene clusters throughout the bacterial phylogenetic tree, bufferins form by far the largest family of RiPPs modified by multinuclear nonheme iron-dependent oxidases (MNIO, DUF692 family). Using Caulobacter vibrioides bufferins as a model, we showed that the conserved Cys residues of their precursors are transformed into 5-thiooxazoles, further expanding the reaction range of MNIO enzymes. This rare modification is installed in conjunction with a partner protein of the DUF2063 family. Bufferin precursors are rare examples of bacterial RiPPs found to feature an N-terminal Sec signal peptide allowing them to be exported by the ubiquitous Sec pathway. We reveal that bufferins are involved in copper homeostasis, and their metal-binding propensity requires the thiooxazole heterocycles. Bufferins enhance bacterial growth under copper stress by complexing excess metal ions. Our study thus describes a large family of RiPP metallophores and unveils a widespread but overlooked metal homeostasis mechanism in bacteria.

Genome Mining Analysis Uncovers the Previously Unknown Biosynthetic Capacity for Secondary Metabolites in Verrucomicrobia

Bacteria of the phylum Verrucomicrobia is widely distributed in diverse ecological environments. Their limited cultivability has greatly caused the significant knowledge gap surrounding their secondary metabolites and their mediating ecological functions. This study delved into the diversity and novelty of secondary metabolite biosynthetic gene clusters (BGCs) of Verrucomicrobia by employing a gene-first approach to investigate 2323 genomes. A total of 7552 BGCs, which encompassed 3744 terpene, 805 polyketide, 773 non-ribosomal peptide gene clusters, and 1933 BGCs of other biosynthetic origins, were identified. They were further classified into 3887 gene cluster families (GCFs) based on biosynthetic gene similarity clustering, of which only six GCFs contained reference biosynthetic gene clusters in the Minimum Information about a Biosynthetic Gene Cluster (MIBiG), indicating the striking novelty of secondary metabolites in Verrucomicrobia. Notably, 37.8% of these gene clusters were harbored by unclassified species of Verrucomicrobia phyla, members of which were highly abundant in soil environments. Furthermore, our comprehensive analysis also revealed Luteolibacter and Methylacidiphilum as the most prolific genera in terms of BGC abundance and diversity, with the discovery of a conservative and new NRPS-PKS BGC in Luteolibacter. This work not only unveiled the biosynthetic potential and genetic diversity of secondary metabolites of Verrucomicrobia but also provided a fresh insight for the exploration of new bioactive compounds.

Nanopore sequencing: flourishing in its teenage years

Over the past decade, nanopore sequencing has experienced significant advancements and changes, transitioning from an initially emerging technology to a significant instrument in the field of genomic sequencing. However, as advancements in next-generation sequencing technology persist, nanopore sequencing also improves. This paper reviews the developments, applications, and outlook on nanopore sequencing technology. Currently, nanopore sequencing supports both DNA and RNA sequencing, making it widely applicable in areas such as telomere-to-telomere (T2T) genome assembly, direct RNA sequencing (DRS), and metagenomics. The openness and versatility of nanopore sequencing have established it as a preferred option for an increasing number of research teams, signaling a transformative influence on life science research. As the nanopore sequencing technology advances, it provides a faster, more cost-effective approach with extended read lengths, demonstrating the significant potential for complex genome assembly, pathogen detection, environmental monitoring, and human disease research, offering a fresh perspective in sequencing technologies.

Exploring the biosynthesis potential of permafrost microbiomes

BACKGROUND

Permafrost microbiomes are of paramount importance for the biogeochemistry of high latitude soils and while endemic biosynthetic domain sequences involved in secondary metabolism have been found in polar surface soils, the biosynthetic potential of permafrost microbiomes remains unexplored. Moreover, the nature of these ecosystems facilitates the unique opportunity to study the distribution and diversity of biosynthetic genes in relic DNA from ancient microbiomes. To explore the biosynthesis potential in permafrost, we used adenylation (AD) domain sequencing to evaluate non-ribosomal peptide (NRP) production in permafrost cores housing microbiomes separated at kilometer and kiloyear scales.

RESULTS

Permafrost microbiomes represented NRP repertoires significantly different from that of temperate soil microbiomes, but as for temperate soils, the estimated domain richness and diversity was strongly correlated to the bacterial taxonomic diversity across locations. Furthermore, we found significant differences in both community composition and AD domain composition across geographical and temporal distances. Overall, the vast majority of biosynthetic domains showed below 90% amino acid similarity to characterized BGCs, confirming the high degree of novelty of NRPs inherent to permafrost microbiomes. Using available metagenomic sequences, we further identified a high biosynthetic diversity beyond NRPs throughout arctic surface soils down to deep and ancient (megayear old) permafrost microbiomes.

CONCLUSION

We have shown that arctic permafrost microbiomes harbor a unique biosynthetic repertoire rich in hitherto undescribed NRPs. This diversity is driven by geographic separation across kilometer scales and by the bacterial taxonomic diversity between microbiomes confined in separate permafrost layers. Hence the permafrost biome represents a unique resource for studying secondary metabolism, and potentially for the discovery of novel drug leads.

Advances in lasso peptide discovery, biosynthesis, and function

Lasso peptides are a large and sequence-diverse class of ribosomally synthesized and post-translationally modified peptide (RiPP) natural products characterized by their slip knot-like shape. These unique, highly stable peptides are produced by bacteria for various purposes. Their stability and sequence diversity make them a potentially useful scaffold for biomedically relevant folded peptides. However, many questions remain about lasso peptide biosynthesis, ecological function, and diversification potential for biomedical and agricultural applications. This review discusses new insights and open questions about lasso peptide biosynthesis and biological function. The role that genome mining has played in the development of new methodologies for discovering and diversifying lasso peptides is also discussed.

Biosynthetic gene clusters from uncultivated soil bacteria of the Atacama Desert

Soil microorganisms mediate several biological processes through the secretion of natural products synthesized in specialized metabolic pathways, yet functional characterization in ecological contexts remains challenging. Using culture-independent metagenomic analyses of microbial DNA derived directly from soil samples, we examined the potential of biosynthetic gene clusters (BGCs) from six bacterial communities distributed along an altitudinal gradient of the Andes Mountains in the Atacama Desert. We mined 38 metagenome-assembled genomes (MAGs) and identified 168 BGCs. Results indicated that most predicted BGCs were classified as non-ribosomal-peptides (NRP), post-translational modified peptides (RiPP), and terpenes, which were mainly identified in genomes of species from Acidobacteriota and Proteobacteria phyla. Based on BGC composition according to types of core biosynthetic genes, six clusters of MAGs were observed, three of them with predominance for a single phylum, of which two also showed specificity to a single sampling site. Comparative analyses of accessory genes in BGCs showed associations between membrane transporters and other protein domains involved in specialized metabolism with classes of biosynthetic cores, such as resistance-nodulation-cell division (RND) multidrug efflux pumps with RiPPs and the iron-dependent transporter TonB with terpenes. Our findings increase knowledge regarding the biosynthetic potential of uncultured bacteria inhabiting pristine locations from one of the oldest and driest nonpolar deserts on Earth.IMPORTANCEMuch of what we know about specialized metabolites in the Atacama Desert, including Andean ecosystems, comes from isolated microorganisms intended for drug development and natural product discovery. To complement research on the metabolic potential of microbes in extreme environments, comparative analyses on functional annotations of biosynthetic gene clusters (BGCs) from uncultivated bacterial genomes were carried out. Results indicated that in general, BGCs encode for structurally unique metabolites and that metagenome-assembled genomes did not show an obvious relationship between the composition of their core biosynthetic potential and taxonomy or geographic distribution. Nevertheless, some members of Acidobacteriota showed a phylogenetic relationship with specific metabolic traits and a few members of Proteobacteria and Desulfobacterota exhibited niche adaptations. Our results emphasize that studying specialized metabolism in environmental samples may significantly contribute to the elucidation of structures, activities, and ecological roles of microbial molecules.

Endophytic Streptomyces: an underexplored source with potential for novel natural drug discovery and development

Streptomyces has long been considered as key sources for natural compounds discovery in medicine and agriculture. These compounds have been demonstrated to possess different biological activities, including antibiotic, antifungal, anticancer, and antiviral effects. As a result, new pharmaceuticals and antibiotics have been developed. Nevertheless, there have been only a few novel discoveries of bioactive compounds in the past decades from Streptomyces in natural habitats. There is, therefore, now a renewed search for new Streptomyces species having the potential to produce many compounds from one strain in lesser explored natural habitats that may be helpful in fighting diseases. Consequently, modern genome mining approaches are imperative for discovering structurally novel natural compounds with therapeutic applications from untapped sources. In light of these facts, endophytic Streptomyces from plants may offer new avenues for the discovery of bioactive compounds with distinctive chemical properties and activities. In the present review, we present the progress made in isolating natural compounds from endophytic Streptomyces originating from plants which have remarkable antimicrobial, cytotoxic, and antifungal properties. A different of distinct structural classes of compounds were reported from endophytic Streptomyces, such as indolosequiterpene, macrolides, flavones, peptides, naphthoquinones, and terpenoids. Further, we discussed modern genomics progress in finding biosynthetic gene clusters (BGCs) encoding compounds. Overall, this review might provide valuable insights into the potential for novel drug discovery from untapped endophytic Streptomyces in the future.

Priestia aryabhattai Improves Soil Environment and Promotes Alfalfa Growth by Enhancing Rhizosphere Microbial Carbon Sequestration Capacity Under Greenhouse Conditions

Plant Growth-Promoting Rhizobacteria (PGPR) are gaining increasing attention, but their interactions with indigenous rhizosphere microbiomes remain unclear. To address this issue, we isolated a strain of Priestia aryabhattai with a growth-promoting effect. Under greenhouse conditions, its growth-promoting effect on alfalfa was evaluated, and amplicon sequencing was used to analyze changes in the rhizosphere microbial community to explore the growth promotion mechanism. Our study shows that inoculation with Priestia aryabhattai increases the α-diversity index of the alfalfa rhizosphere microbiome and enhances the abundance of beneficial bacterial genera. This is likely because inoculation with Priestia aryabhattai increased the abundance of carbon-sequestering genera, particularly Gemmatimonas, thereby improving the soil environment. The increased abundance of beneficial bacteria stimulates root development in alfalfa and enhances nutrient uptake, particularly phosphorus, which in turn boosts photosynthesis and promotes alfalfa growth. In summary, Priestia aryabhattai improves soil environment and promotes alfalfa growth by enhancing the carbon sequestration capacity of the rhizosphere microbial community. This work provides theoretical support and insight for the development of PGPR inoculants and for further research on their mechanisms.

Comparative genomics unravels a rich set of biosynthetic gene clusters with distinct evolutionary trajectories across fungal species (Termitomyces) farmed by termites

The use of compounds produced by hosts or symbionts for defence against antagonists has been identified in many organisms, including in fungus-farming termites (Macrotermitinae). The obligate mutualistic fungus Termitomyces plays a pivotal role in plant biomass decomposition and as the primary food source for these termites. Despite the isolation of various specialized metabolites from different Termitomyces species, our grasp of their natural product repertoire remains incomplete. To address this knowledge gap, we conducted a comprehensive analysis of 39 Termitomyces genomes, representing 21 species associated with members of five termite host genera. We identified 754 biosynthetic gene clusters (BGCs) coding for specialized metabolites and categorized 660 BGCs into 61 biosynthetic gene cluster families (GCFs) spanning five compound classes. Seven GCFs were shared by all 21 Termitomyces species and 21 GCFs were present in all genomes of subsets of species. Evolutionary constraint analyses on the 25 most abundant GCFs revealed distinctive evolutionary histories, signifying that millions of years of termite-fungus symbiosis have influenced diverse biosynthetic pathways. This study unveils a wealth of non-random and largely undiscovered chemical potential within Termitomyces and contributes to our understanding of the intricate evolutionary trajectories of biosynthetic gene clusters in the context of long-standing symbiosis.

The impacts of ecological disturbances on the diversity of biosynthetic gene clusters in kauri (Agathis australis) soil

BACKGROUND

The ancient kauri (Agathis australis) dominated forests of Aotearoa New Zealand are under threat from a multitude of ecological disturbances such as forest fragmentation, biodiversity loss, climate change, and the spread of the virulent soil pathogen Phytophthora agathidicida. Taking a wider ecosystem-level approach, our research aimed to explore the impacts of forest disturbance and disease outbreaks on the biosynthetic potential and taxonomic diversity of the kauri soil microbiome. We explored the diversity of secondary metabolite biosynthetic gene clusters (BGCs) in soils from a range of kauri forests that varied according to historical disturbance and dieback expression. To characterise the diversity of microbial BGCs, we targeted the non-ribosomal peptide synthetase (NRPS) and polyketide synthetase (PKS) gene regions for sequencing using long-read PacBio® HiFi sequencing. Furthermore, the soil bacterial and fungal communities of each forest were characterized using 16 S rRNA and ITS gene region sequencing.

RESULTS

We identified a diverse array of naturally occurring microbial BGCs in the kauri forest soils, which may offer promising targets for the exploration of secondary metabolites with anti-microbial activity against P. agathidicida. We detected differences in the number and diversity of microbial BGCs according to forest disturbance history. Notably, soils associated with the most undisturbed kauri forest had a higher number and diversity of microbial NRPS-type BGCs, which may serve as a potential indicator of natural levels of microbiome resistance to pathogen invasion.

CONCLUSIONS

By linking patterns in microbial biosynthetic diversity to forest disturbance history, this research highlights the need for us to consider the influence of ecological disturbances in potentially predisposing forests to disease by impacting the wider health of forest soil ecosystems. Furthermore, by identifying the range of microbial BGCs present at a naturally high abundance in kauri soils, this research contributes to the future discovery of natural microbial compounds that may potentially enhance the disease resilience of kauri forests. The methodological approaches used in this study highlight the value of moving beyond a taxonomic lens when examining the response of microbial communities to ecosystem disturbance and the need to develop more functional measures of microbial community resilience to invasive plant pathogens.

Exploring the secrets of marine microorganisms: Unveiling secondary metabolites through metagenomics

Marine microorganisms are increasingly recognized as primary producers of marine secondary metabolites, drawing growing research interest. Many of these organisms are unculturable, posing challenges for study. Metagenomic techniques enable research on these unculturable microorganisms, identifying various biosynthetic gene clusters (BGCs) related to marine microbial secondary metabolites, thereby unveiling their secrets. This review comprehensively analyses metagenomic methods used in discovering marine microbial secondary metabolites, highlighting tools commonly employed in BGC identification, and discussing the potential and challenges in this field. It emphasizes the key role of metagenomics in unveiling secondary metabolites, particularly in marine sponges and tunicates. The review also explores current limitations in studying these metabolites through metagenomics, noting how long-read sequencing technologies and the evolution of computational biology tools offer more possibilities for BGC discovery. Furthermore, the development of synthetic biology allows experimental validation of computationally identified BGCs, showcasing the vast potential of metagenomics in mining marine microbial secondary metabolites.

Metagenomic Insights into Potential Impacts of Antibacterial Biosynthesis and Anthropogenic Activity on Nationwide Soil Resistome

The presence of antibiotic resistance genes (ARGs) in soils has received extensive attention regarding its impacts on environmental, animal, and human systems under One Health. However, the health risks of soil ARGs and microbial determinants of soil resistomes remain poorly understood. Here, a nationwide metagenomic investigation of ARGs in cropland and forest soils in China was conducted. The findings indicated that the abundance and richness of high-risk (i.e., mobilizable, pathogen-carriable and clinically relevant) ARGs in cropland soils were 25.7 times and 8.4 times higher, respectively, compared to those identified in forest soils, suggesting the contribution of agricultural practices to the elevated risk level of soil resistomes. The biosynthetic potential of antibacterials best explained the total ARG abundance (Mantel's r = 0.52, p < 0.001) when compared with environmental variables and anthropogenic disturbance. Both microbial producers' self-resistance and antagonistic interactions contributed to the ARG abundance, of which self-resistance ARGs account for 14.1 %- 35.1 % in abundance. With the increased biosynthetic potential of antibacterials, the antagonistic interactions within the microbial community were greatly enhanced, leading to a significant increase in ARG abundance. Overall, these findings advance our understanding of the emergence and dissemination of soil ARGs and provide critical implications for the risk control of soil resistomes.

Unveiling genomic features linked to traits of plant growth-promoting bacterial communities from sugarcane

Microorganisms are ubiquitous, and those inhabiting plants have been the subject of several studies. Plant-associated bacteria exhibit various biological mechanisms that enable them to colonize host plants and, in some cases, enhance their fitness. In this study, we describe the genomic features predicted to be associated with plant growth-promoting traits in six bacterial communities isolated from sugarcane. The use of highly accurate single-molecule real-time sequencing technology for metagenomic samples from these bacterial communities allowed us to recover 17 genomes. The taxonomic assignments for the binned genomes were performed, revealing taxa distributed across three main phyla: Bacillota, Bacteroidota, and Pseudomonadota, with the latter being the most representative. Subsequently, we functionally annotated the metagenome-assembled genomes (MAGs) to characterize their metabolic pathways related to plant growth-promoting traits. Our study successfully identified the enrichment of important functions related to phosphate and potassium acquisition, modulation of phytohormones, and mechanisms for coping with abiotic stress. These findings could be linked to the robust colonization of these sugarcane endophytes.

Shotgun metagenomic insights into secondary metabolite biosynthetic gene clusters reveal taxonomic and functional profiles of microbiomes in natural farmland soil

Antibiotic resistance is a worldwide problem that imposes a devastating effect on developing countries and requires immediate interventions. Initially, most of the antibiotic drugs were identified by culturing soil microbes. However, this method is prone to discovering the same antibiotics repeatedly. The present study employed a shotgun metagenomics approach to investigate the taxonomic diversity, functional potential, and biosynthetic capacity of microbiomes from two natural agricultural farmlands located in Bekeka and Welmera Choke Kebelle in Ethiopia for the first time. Analysis of the small subunit rRNA revealed bacterial domain accounting for 83.33% and 87.24% in the two selected natural farmlands. Additionally, the analysis showed the dominance of Proteobacteria representing 27.27% and 28.79% followed by Actinobacteria making up 12.73% and 13.64% of the phyla composition. Furthermore, the analysis revealed the presence of unassigned bacteria in the studied samples. The metagenome functional analysis showed 176,961 and 104, 636 number of protein-coding sequences (pCDS) from the two samples found a match with 172,655 and 102, 275 numbers of InterPro entries, respectively. The Genome ontology annotation suggests the presence of 5517 and 3293 pCDS assigned to the "biosynthesis process". Numerous Kyoto Encyclopedia of Genes and Genomes modules (KEGG modules) involved in the biosynthesis of terpenoids and polyketides were identified. Furthermore, both known and novel Biosynthetic gene clusters, responsible for the production of secondary metabolites, such as polyketide synthases, non-ribosomal peptide synthetase, ribosomally synthesized and post-translationally modified peptides (Ripp), and Terpene, were discovered. Generally, from the results it can be concluded that the microbiomes in the selected sampling sites have a hidden functional potential for the biosynthesis of secondary metabolites. Overall, this study can serve as a strong preliminary step in the long journey of bringing new antibiotics to the market.

Unravelling biosynthesis and biodegradation potentials of microbial dark matters in hypersaline lakes

Biosynthesis and biodegradation of microorganisms critically underpin the development of biotechnology, new drugs and therapies, and environmental remediation. However, most uncultured microbial species along with their metabolic capacities in extreme environments, remain obscured. Here we unravel the metabolic potential of microbial dark matters (MDMs) in four deep-inland hypersaline lakes in Xinjiang, China. Utilizing metagenomic binning, we uncovered a rich diversity of 3030 metagenome-assembled genomes (MAGs) across 82 phyla, revealing a substantial portion, 2363 MAGs, as previously unclassified at the genus level. These unknown MAGs displayed unique distribution patterns across different lakes, indicating a strong correlation with varied physicochemical conditions. Our analysis revealed an extensive array of 9635 biosynthesis gene clusters (BGCs), with a remarkable 9403 being novel, suggesting untapped biotechnological potential. Notably, some MAGs from potentially new phyla exhibited a high density of these BGCs. Beyond biosynthesis, our study also identified novel biodegradation pathways, including dehalogenation, anaerobic ammonium oxidation (Anammox), and degradation of polycyclic aromatic hydrocarbons (PAHs) and plastics, in previously unknown microbial clades. These findings significantly enrich our understanding of biosynthesis and biodegradation processes and open new avenues for biotechnological innovation, emphasizing the untapped potential of microbial diversity in hypersaline environments.

Unlocking the biosynthetic potential and taxonomy of the Antarctic microbiome along temporal and spatial gradients

Extreme environments, such as Antarctica, select microbial communities that display a range of evolutionary strategies to survive and thrive under harsh environmental conditions. These include a diversity of specialized metabolites, which have the potential to be a source for new natural product discovery. Efforts using (meta)genome mining approaches to identify and understand biosynthetic gene clusters in Antarctica are still scarce, and the extent of their diversity and distribution patterns in the environment have yet to be discovered. Herein, we investigated the biosynthetic gene diversity of the biofilm microbial community of Whalers Bay, Deception Island, in the Antarctic Peninsula and revealed its distribution patterns along spatial and temporal gradients by applying metagenome mining approaches and multivariable analysis. The results showed that the Whalers Bay microbial community harbors a great diversity of biosynthetic gene clusters distributed into seven classes, with terpene being the most abundant. The phyla Proteobacteria and Bacteroidota were the most abundant in the microbial community and contributed significantly to the biosynthetic gene abundances in Whalers Bay. Furthermore, the results highlighted a significant correlation between the distribution of biosynthetic genes and taxonomic diversity, emphasizing the intricate interplay between microbial taxonomy and their potential for specialized metabolite production.IMPORTANCEThis research on antarctic microbial biosynthetic diversity in Whalers Bay, Deception Island, unveils the hidden potential of extreme environments for natural product discovery. By employing metagenomic techniques, the research highlights the extensive diversity of biosynthetic gene clusters and identifies key microbial phyla, Proteobacteria and Bacteroidota, as significant contributors. The correlation between taxonomic diversity and biosynthetic gene distribution underscores the intricate interplay governing specialized metabolite production. These findings are crucial for understanding microbial adaptation in extreme environments and hold significant implications for bioprospecting initiatives. The study opens avenues for discovering novel bioactive compounds with potential applications in medicine and industry, emphasizing the importance of preserving and exploring these polyextreme ecosystems to advance biotechnological and pharmaceutical research.

Biosynthetic potential of uncultured anammox community bacteria revealed through multi-omics analysis

Microbial secondary metabolites (SMs) and their derivatives have been widely used in medicine, agriculture, and energy. Growing needs for renewable energy and the challenges posed by antibiotic resistance, cancer, and pesticides emphasize the crucial hunt for new SMs. Anaerobic ammonium-oxidation (anammox) systems harbor many uncultured or underexplored bacteria, representing potential resources for discovering novel SMs. Leveraging HiFi long-read metagenomic sequencing, 1,040 biosynthetic gene clusters (BGCs) were unearthed from the anammox microbiome with 58% being complete and showcasing rich diversity. Most of them showed distant relations to known BGCs, implying novelty. Members of the underexplored lineages (Chloroflexota and Planctomycetota) and Proteobacteria contained lots of BGCs, showcasing substantial biosynthetic potential. Metaproteomic results indicated that Planctomycetota members harbored the most active BGCs, particularly those involved in producing potential biofuel-ladderane. Overall, these findings underscore that anammox microbiomes could serve as valuable resources for mining novel BGCs and discovering new SMs for practical application.

Exploring the roles of ribosomal peptides in prokaryote-phage interactions through deep learning-enabled metagenome mining

BACKGROUND

Microbial secondary metabolites play a crucial role in the intricate interactions within the natural environment. Among these metabolites, ribosomally synthesized and post-translationally modified peptides (RiPPs) are becoming a promising source of therapeutic agents due to their structural diversity and functional versatility. However, their biosynthetic capacity and ecological functions remain largely underexplored.

RESULTS

Here, we aim to explore the biosynthetic profile of RiPPs and their potential roles in the interactions between microbes and viruses in the ocean, which encompasses a vast diversity of unique biomes that are rich in interactions and remains chemically underexplored. We first developed TrRiPP to identify RiPPs from ocean metagenomes, a deep learning method that detects RiPP precursors in a hallmark gene-independent manner to overcome the limitations of classic methods in processing highly fragmented metagenomic data. Applying this method to metagenomes from the global ocean microbiome, we uncover a diverse array of previously uncharacterized putative RiPP families with great novelty and diversity. Through correlation analysis based on metatranscriptomic data, we observed a high prevalence of antiphage defense-related and phage-related protein families that were co-expressed with RiPP families. Based on this putative association between RiPPs and phage infection, we constructed an Ocean Virus Database (OVD) and established a RiPP-involving host-phage interaction network through host prediction and co-expression analysis, revealing complex connectivities linking RiPP-encoding prokaryotes, RiPP families, viral protein families, and phages. These findings highlight the potential of RiPP families involved in prokaryote-phage interactions and coevolution, providing insights into their ecological functions in the ocean microbiome.

CONCLUSIONS

This study provides a systematic investigation of the biosynthetic potential of RiPPs from the ocean microbiome at a global scale, shedding light on the essential insights into the ecological functions of RiPPs in prokaryote-phage interactions through the integration of deep learning approaches, metatranscriptomic data, and host-phage connectivity. This study serves as a valuable example of exploring the ecological functions of bacterial secondary metabolites, particularly their associations with unexplored microbial interactions. Video Abstract.

A vast repertoire of secondary metabolites potentially influences community dynamics and biogeochemical processes in cold seeps

In deep-sea cold seeps, microbial communities thrive on the geological seepage of hydrocarbons and inorganic compounds, differing from photosynthetically driven ecosystems. However, their biosynthetic capabilities remain largely unexplored. Here, we analyzed 81 metagenomes, 33 metatranscriptomes, and 7 metabolomes derived from nine different cold seep areas to investigate their secondary metabolites. Cold seep microbiomes encode diverse and abundant biosynthetic gene clusters (BGCs). Most BGCs are affiliated with understudied bacteria and archaea, including key mediators of methane and sulfur cycling. The BGCs encode diverse antimicrobial compounds that potentially shape community dynamics and various metabolites predicted to influence biogeochemical cycling. BGCs from key players are widely distributed and highly expressed, with their abundance and expression levels varying with sediment depth. Sediment metabolomics reveals unique natural products, highlighting uncharted chemical potential and confirming BGC activity in these sediments. Overall, these results demonstrate that cold seep sediments serve as a reservoir of hidden natural products and sheds light on microbial adaptation in chemosynthetically driven ecosystems.

Diversity and distribution of biosynthetic gene clusters in agricultural soil microbiomes

Bacterial secondary metabolites serve as an important source of molecules for drug discovery. They also play an important function in mediating the interactions of microbial producers with their living environment and surrounding organisms. However, little is known about the genetic novelty, distribution, and community-level impacts of soil bacterial biosynthetic potential on a large geographic scale. Here, we constructed the first catalog of 11,149 biosynthetic gene clusters (BGCs) from agricultural soils across China and unearthed hidden biosynthetic potential for new natural product discovery from the not-yet-cultivated soil bacteria. Notably, we revealed soil pH as the strongest environmental driver of BGC biogeography and predicted that soil acidification and global climate change could damage the biosynthetic potential of the soil microbiome. The co-occurrence network of bacterial genomes revealed two BGC-rich species, i.e., Nocardia niigatensis from Actinobacteriota and PSRF01 from Acidobacteriota, as the module hub and connector, respectively, indicating their keystone positions in the soil microbial communities. We also uncovered a dominant role of BGC-inferred biotic interactions over environmental drivers in structuring the soil microbiome. Overall, this study achieved novel insights into the BGC landscape in agricultural soils of China, substantially expanding our understanding of the diversity and novelty of bacterial secondary metabolism and the potential role of secondary metabolites in microbiota assembly.IMPORTANCEBacterial secondary metabolites not only serve as the foundation for numerous therapeutics (e.g., antibiotics and anticancer drugs), but they also play critical ecological roles in mediating microbial interactions (e.g., competition and communication). However, our knowledge of bacterial secondary metabolism is limited to only a small fraction of cultured strains, thus restricting our comprehensive understanding of their diversity, novelty, and potential ecological roles in soil ecosystems. Here, we used culture-independent metagenomics to explore biosynthetic potentials in agricultural soils of China. Our analyses revealed a high degree of genetic diversity and novelty within biosynthetic gene clusters in agricultural soil environments, offering valuable insights for biochemists seeking to synthesize novel bioactive products. Furthermore, we uncovered the pivotal role of BGC-rich species in microbial communities and the significant relationship between BGC richness and microbial phylogenetic turnover. This information emphasizes the importance of biosynthetic potential in the assembly of microbial communities.

SecMet-FISH: labeling, visualization, and enumeration of secondary metabolite producing microorganisms

Our understanding of the role of secondary metabolites in microbial communities is challenged by intrinsic limitations of culturing bacteria under laboratory conditions and hence cultivation independent approaches are needed. Here, we present a protocol termed Secondary Metabolite FISH (SecMet-FISH), combining advantages of gene-targeted fluorescence in situ hybridization (geneFISH) with in-solution methods (in-solution FISH) to detect and quantify cells based on their genetic capacity to produce secondary metabolites. The approach capitalizes on the conserved nature of biosynthetic gene clusters (BGCs) encoding adenylation (AD) and ketosynthase (KS) domains, and thus selectively targets the genetic basis of non-ribosomal peptide and polyketide biosynthesis. The concept relies on the generation of amplicon pools using degenerate primers broadly targeting AD and KS domains followed by fluorescent labeling, detection, and quantification. Initially, we obtained AD and KS amplicons from Pseuodoalteromonas rubra, which allowed us to successfully label and visualize BGCs within P. rubra cells, demonstrating the feasibility of SecMet-FISH. Next, we adapted the protocol and optimized it for hybridization in both Gram-negative and Gram-positive bacterial cell suspensions, enabling high-throughput single cell analysis by flow cytometry. Ultimately, we used SecMet-FISH to successfully distinguish secondary metabolite producers from non-producers in a five-member synthetic community.

Inoculation with adapted bacterial communities promotes development of full scale slow sand filters for drinking water production

Gravity-driven filtration through slow sand filters (SSFs) is one of the oldest methods for producing drinking water. As water passes through a sand bed, undesired microorganisms and chemicals are removed by interactions with SSF biofilm and its resident microbes. Despite their importance, the processes through which these microbial communities form are largely unknown, as are the factors affecting these processes. In this study, two SSFs constructed using different sand sources were compared to an established filter and observed throughout their maturation process. One SSF was inoculated through addition of sand scraped from established filters, while the other was not inoculated. The operational and developing microbial communities of SSFs, as well as their influents and effluents, were studied by sequencing of 16S ribosomal rRNA genes. A functional microbial community resembling that of the established SSF was achieved in the inoculated SSF, but not in the non-inoculated SSF. Notably, the non-inoculated SSF had significantly (p < 0.01) higher abundances of classes Armatimonadia, Elusimicrobia, Fimbriimonadia, OM190 (phylum Planctomycetota), Parcubacteria, Vampirivibrionia and Verrucomicrobiae. Conversely, it had lower abundances of classes Anaerolineae, Bacilli, bacteriap25 (phylum Myxococcota), Blastocatellia, Entotheonellia, Gemmatimonadetes, lineage 11b (phylum Elusimicrobiota), Nitrospiria, Phycisphaerae, subgroup 22 (phylum Acidobacteriota) and subgroup 11 (phylum Acidobacteriota). Poor performance of neutral models showed that the assembly and dispersal of SSF microbial communities was mainly driven by selection. The temporal turnover of microbial species, as estimated through the scaling exponent of the species-time relationship, was twice as high in the non-inoculated filter (0.946 ± 0.164) compared to the inoculated filter (0.422 ± 0.0431). This study shows that the addition of an inoculum changed the assembly processes within SSFs. Specifically, the rate at which new microorganisms were observed in the biofilm was reduced. The reduced temporal turnover may be driven by inoculating taxa inhibiting growth, potentially via secondary metabolite production. This in turn would allow the inoculation community to persist and contribute to SSF function.

BASALT refines binning from metagenomic data and increases resolution of genome-resolved metagenomic analysis

Metagenomic binning is an essential technique for genome-resolved characterization of uncultured microorganisms in various ecosystems but hampered by the low efficiency of binning tools in adequately recovering metagenome-assembled genomes (MAGs). Here, we introduce BASALT (Binning Across a Series of Assemblies Toolkit) for binning and refinement of short- and long-read sequencing data. BASALT employs multiple binners with multiple thresholds to produce initial bins, then utilizes neural networks to identify core sequences to remove redundant bins and refine non-redundant bins. Using the same assemblies generated from Critical Assessment of Metagenome Interpretation (CAMI) datasets, BASALT produces up to twice as many MAGs as VAMB, DASTool, or metaWRAP. Processing assemblies from a lake sediment dataset, BASALT produces ~30% more MAGs than metaWRAP, including 21 unique class-level prokaryotic lineages. Functional annotations reveal that BASALT can retrieve 47.6% more non-redundant opening-reading frames than metaWRAP. These results highlight the robust handling of metagenomic sequencing data of BASALT.

Connecting molecular biomarkers, mineralogical composition, and microbial diversity from Mars analog lava tubes

Lanzarote (Canary Islands, Spain) is one of the best terrestrial analogs to Martian volcanology. Particularly, Lanzarote lava tubes may offer access to recognizably preserved chemical and morphological biosignatures valuable for astrobiology. By combining microbiological, mineralogical, and organic geochemistry tools, an in-depth characterization of speleothems and associated microbial communities in lava tubes of Lanzarote is provided. The aim is to untangle the underlying factors influencing microbial colonization in Earth's subsurface to gain insight into the possibility of similar subsurface microbial habitats on Mars and to identify biosignatures preserved in lava tubes unequivocally. The microbial communities with relevant representativeness comprise chemoorganotrophic, halophiles, and/or halotolerant bacteria that have evolved as a result of the surrounding oceanic environmental conditions. Many of these bacteria have a fundamental role in reshaping cave deposits due to their carbonatogenic ability, leaving behind an organic record that can provide evidence of past or present life. Based on functional profiling, we infer that Crossiella is involved in fluorapatite precipitation via urea hydrolysis and propose its Ca-rich precipitates as compelling biosignatures valuable for astrobiology. In this sense, analytical pyrolysis, stable isotope analysis, and chemometrics were conducted to characterize the complex organic fraction preserved in the speleothems and find relationships among organic families, microbial taxa, and precipitated minerals. We relate organic compounds with subsurface microbial taxa, showing that organic families drive the microbiota of Lanzarote lava tubes. Our data indicate that bacterial communities are important contributors to biomarker records in volcanic-hosted speleothems. Within them, the lipid fraction primarily consists of low molecular weight n-alkanes, α-alkenes, and branched-alkenes, providing further evidence that microorganisms serve as the origin of organic matter in these formations. The ongoing research in Lanzarote's lava tubes will help develop protocols, routines, and predictive models that could provide guidance on choosing locations and methodologies for searching potential biosignatures on Mars.

Metagenomic insights into novel microbial lineages with distinct ecological functions in the Arctic glacier foreland ecosystems

Land-terminating glaciers are retreating globally, resulting in the expansion of the ice-free glacier forelands (GFs). These GFs act as a natural laboratory to study microbial community succession, soil formation, and ecosystem development. Here, we have employed gene-centric and genome-resolved metagenomic approaches to disseminate microbial diversity, community structure, and their associated biogeochemical processes involved in the carbon, nitrogen, and sulfur cycling across three GF ecosystems. Here, we present a compendium of draft Metagenome Assembled Genomes (MAGs) belonging to bacterial (n = 899) and archaeal (n = 4) domains. These MAGs were reconstructed using a total of 27 shotgun metagenomic datasets obtained from three different GFs, including Midtre Lovénbreen glacier (Svalbard), Russell glacier (Greenland), and Storglaciaren (Sweden). The taxonomic classification revealed that 98% of MAGs remained unclassified at species levels, suggesting the presence of novel microbial lineages. The abundance of metabolic genes associated with carbon, nitrogen, and sulfur cycling pathways varied between and within the samples collected across the three GF ecosystems. Our findings indicate that MAGs from different GFs share close phylogenetic relationships but exhibit significant differences in abundance, distribution patterns, and metabolic functions. This compendium of novel MAGs, encompassing autotrophic, phototrophic, and chemolithoautotrophic microbial groups reconstructed from GF ecosystems, represents a valuable resource for further studies.

Bacterial community and culturable actinomycetes of Phyllostachys viridiglaucescens rhizosphere

During the course of development plants form tight interactions with microorganisms inhabiting their root zone. In turn, rhizosphere bacteria, in particular members of the phylum Actinomycetota, positively influence the host plant by increasing access to essential nutrients and controlling the pathogenic microorganism's population. Herein, we report the characterisation of the rhizosphere associated actinobacteria community of Phyllostachys viridiglaucescens growing in the Nikitsky Botanical Garden (Crimean Peninsula, Ukraine). The overall composition of the bacterial community was elucidated by 16S rRNA gene amplicon sequencing followed by isolation of culturable microorganisms with the focus on actinomycetes. The metagenomic approach revealed that the representatives of phylum Actinomycetota (57.1%), Pseudomonadota (20.0%), and Acidobacteriota (12.2%) were dominating in the studied microbiome with Ilumatobacter (phylum Actinomycetota) (13.1%) being the dominant genus. Furthermore, a total of 159 actinomycete isolates, belonging to eight genera of Streptomyces, Micromonospora, Nonomuraea, Arthrobacter, Actinomadura, Kribbella, Cellulosimicrobium, and Mumia, were recovered from P. viridiglaucescens rhizosphere. The isolated species were tested for antimicrobial activity. 64% of isolates were active against at least one bacterial test-culture and 7.5% against fungal test culture. In overall, the rhizosphere bacterial communities act as a great source of actinobacterial diversity with the high potential for production of new bioactive compounds.

Biosynthetic potential of the gut microbiome in longevous populations

Gut microbiome plays a pivotal role in combating diseases and facilitating healthy aging, and natural products derived from biosynthetic gene clusters (BGCs) of the human microbiome exhibit significant biological activities. However, the natural products of the gut microbiome in long-lived populations remain poorly understood. Here, we integrated six cohorts of long-lived populations, encompassing a total of 1029 fecal metagenomic samples, and employed the metagenomic single sample assembled BGCs (MSSA-BGCs) analysis pipeline to investigate the natural products and their associated species. Our findings reveal that the BGC composition of the extremely long-lived group differed significantly from that of younger elderly and young individuals across five cohorts. Terpene and Type I PKS BGCs were enriched in the extremely long-lived, whereas cyclic-lactone-autoinducer BGCs were more prevalent in the young. Association analysis indicated that terpene BGCs were strongly associated with the abundance of Akkermansia muciniphila, which was also more abundant in the long-lived elderly across at least three cohorts. We assembled 18 A. muciniphila draft genomes using metagenomic data from the extremely long-lived group across six cohorts and discovered that they all harbor two classes of terpene BGCs, which aligns with the 97 complete genomes of A. muciniphila strains retrieved from the NCBI database. The core domains of these two BGC classes are squalene/phytoene synthases involved in the biosynthesis of tri- and tetraterpenes. Furthermore, the abundance of fecal A. muciniphila was significantly associated with eight types of triterpenoids. Targeted terpenoid metabolomic analysis revealed that two triterpenoids, Holstinone C and colubrinic acid, were enriched in the A. muciniphila culture solution compared to the medium, thereby confirming the production of triterpenoids by A. muciniphila. The natural products derived from the gut of long-lived populations provide intriguing indications of their potential beneficial roles in regulating health.

A genomic catalogue of soil microbiomes boosts mining of biodiversity and genetic resources

Soil harbors a vast expanse of unidentified microbes, termed as microbial dark matter, presenting an untapped reservo)ir of microbial biodiversity and genetic resources, but has yet to be fully explored. In this study, we conduct a large-scale excavation of soil microbial dark matter by reconstructing 40,039 metagenome-assembled genome bins (the SMAG catalogue) from 3304 soil metagenomes. We identify 16,530 of 21,077 species-level genome bins (SGBs) as unknown SGBs (uSGBs), which expand archaeal and bacterial diversity across the tree of life. We also illustrate the pivotal role of uSGBs in augmenting soil microbiome's functional landscape and intra-species genome diversity, providing large proportions of the 43,169 biosynthetic gene clusters and 8545 CRISPR-Cas genes. Additionally, we determine that uSGBs contributed 84.6% of previously unexplored viral-host associations from the SMAG catalogue. The SMAG catalogue provides an useful genomic resource for further studies investigating soil microbial biodiversity and genetic resources.

Present and future outlooks on environmental DNA-based methods for antibiotic discovery

Novel antibiotics are in constant demand to combat a global increase in antibiotic-resistant infections. Bacterial natural products have been a long-standing source of antibiotic compounds, and metagenomic mining of environmental DNA (eDNA) has increasingly provided new antibiotic leads. The metagenomic small-molecule discovery pipeline can be divided into three main steps: surveying eDNA, retrieving a sequence of interest, and accessing the encoded natural product. Improvements in sequencing technology, bioinformatic algorithms, and methods for converting biosynthetic gene clusters into small molecules are steadily increasing our ability to discover metagenomically encoded antibiotics. We predict that, over the next decade, ongoing technological improvements will dramatically increase the rate at which antibiotics are discovered from metagenomes.

Long-Read Metagenomics of Marine Microbes Reveals Diversely Expressed Secondary Metabolites

Microbial secondary metabolites play crucial roles in microbial competition, communication, resource acquisition, antibiotic production, and a variety of other biotechnological processes. The retrieval of full-length BGC (biosynthetic gene cluster) sequences from uncultivated bacteria is difficult due to the technical constraints of short-read sequencing, making it impossible to determine BGC diversity. Using long-read sequencing and genome mining, 339 mainly full-length BGCs were recovered in this study, illuminating the wide range of BGCs from uncultivated lineages discovered in seawater from Aoshan Bay, Yellow Sea, China. Many extremely diverse BGCs were discovered in bacterial phyla such as Proteobacteria, Bacteroidota, Acidobacteriota, and Verrucomicrobiota as well as the previously uncultured archaeal phylum "Candidatus Thermoplasmatota." The data from metatranscriptomics showed that 30.1% of secondary metabolic genes were being expressed, and they also revealed the expression pattern of BGC core biosynthetic genes and tailoring enzymes. Taken together, our results demonstrate that long-read metagenomic sequencing combined with metatranscriptomic analysis provides a direct view into the functional expression of BGCs in environmental processes. IMPORTANCE Genome mining of metagenomic data has become the preferred method for the bioprospecting of novel compounds by cataloguing secondary metabolite potential. However, the accurate detection of BGCs requires unfragmented genomic assemblies, which have been technically difficult to obtain from metagenomes until recently with new long-read technologies. We used high-quality metagenome-assembled genomes generated from long-read data to determine the biosynthetic potential of microbes found in the surface water of the Yellow Sea. We recovered 339 highly diverse and mostly full-length BGCs from largely uncultured and underexplored bacterial and archaeal phyla. Additionally, we present long-read metagenomic sequencing combined with metatranscriptomic analysis as a potential method for gaining access to the largely underutilized genetic reservoir of specialized metabolite gene clusters in the majority of microbes that are not cultured. The combination of long-read metagenomic and metatranscriptomic analyses is significant because it can more accurately assess the mechanisms of microbial adaptation to the environment through BGC expression based on metatranscriptomic data.

A Comprehensive Self-Resistance Gene Database for Natural-Product Discovery with an Application to Marine Bacterial Genome Mining

In the world of microorganisms, the biosynthesis of natural products in secondary metabolism and the self-resistance of the host always occur together and complement each other. Identifying resistance genes from biosynthetic gene clusters (BGCs) helps us understand the self-defense mechanism and predict the biological activity of natural products synthesized by microorganisms. However, a comprehensive database of resistance genes is still lacking, which hinders natural product annotation studies in large-scale genome mining. In this study, we compiled a resistance gene database (RGDB) by scanning the four available databases: CARD, MIBiG, NCBIAMR, and UniProt. Every resistance gene in the database was annotated with resistance mechanisms and possibly involved chemical compounds, using manual annotation and transformation from the resource databases. The RGDB was applied to analyze resistance genes in 7432 BGCs in 1390 genomes from a marine microbiome project. Our calculation showed that the RGDB successfully identified resistance genes for more than half of the BGCs, suggesting that the database helps prioritize BGCs that produce biologically active natural products.

Chromosomal organization of biosynthetic gene clusters, including those of nine novel species, suggests plasticity of myxobacterial specialized metabolism

Introduction

Natural products discovered from bacteria provide critically needed therapeutic leads for drug discovery, and myxobacteria are an established source for metabolites with unique chemical scaffolds and biological activities. Myxobacterial genomes accommodate an exceptional number and variety of biosynthetic gene clusters (BGCs) which encode for features involved in specialized metabolism.

Methods

In this study, we describe the collection, sequencing, and genome mining of 20 myxobacteria isolated from rhizospheric soil samples collected in North America.

Results

Nine isolates were determined to be novel species of myxobacteria including representatives from the genera Archangium, Myxococcus, Nannocystis, Polyangium, Pyxidicoccus, Sorangium, and Stigmatella. Growth profiles, biochemical assays, and descriptions were provided for all proposed novel species. We assess the BGC content of all isolates and observe differences between Myxococcia and Polyangiia clusters.

Discussion

Continued discovery and sequencing of novel myxobacteria from the environment provide BGCs for the genome mining pipeline. Utilizing complete or near-complete genome sequences, we compare the chromosomal organization of BGCs of related myxobacteria from various genera and suggest that the spatial proximity of hybrid, modular clusters contributes to the metabolic adaptability of myxobacteria.

Novel Gene Clusters for Natural Product Synthesis Are Abundant in the Mangrove Swamp Microbiome

Natural microbial communities produce a diverse array of secondary metabolites with ecologically and biotechnologically relevant activities. Some of them have been used clinically as drugs, and their production pathways have been identified in a few culturable microorganisms. However, since the vast majority of microorganisms in nature have not been cultured, identifying the synthetic pathways of these metabolites and tracking their hosts remain a challenge. The microbial biosynthetic potential of mangrove swamps remains largely unknown. Here, we examined the diversity and novelty of biosynthetic gene clusters in dominant microbial populations in mangrove wetlands by mining 809 newly reconstructed draft genomes and probing the activities and products of these clusters by using metatranscriptomic and metabolomic techniques. A total of 3,740 biosynthetic gene clusters were identified from these genomes, including 1,065 polyketide and nonribosomal peptide gene clusters, 86% of which showed no similarity to known clusters in the Minimum Information about a Biosynthetic Gene Cluster (MIBiG) repository. Of these gene clusters, 59% were harbored by new species or lineages of Desulfobacterota-related phyla and Chloroflexota, whose members are highly abundant in mangrove wetlands and for which few synthetic natural products have been reported. Metatranscriptomics revealed that most of the identified gene clusters were active in field and microcosm samples. Untargeted metabolomics was also used to identify metabolites from the sediment enrichments, and 98% of the mass spectra generated were unrecognizable, further supporting the novelty of these biosynthetic gene clusters. Our study taps into a corner of the microbial metabolite reservoir in mangrove swamps, providing clues for the discovery of new compounds with valuable activities. IMPORTANCE At present, the majority of known clinical drugs originated from cultivated species of a few bacterial lineages. It is vital for the development of new pharmaceuticals to explore the biosynthetic potential of naturally uncultivable microorganisms using new techniques. Based on the large numbers of genomes reconstructed from mangrove wetlands, we identified abundant and diverse biosynthetic gene clusters in previously unsuspected phylogenetic groups. These gene clusters exhibited a variety of organizational architectures, especially for nonribosomal peptide synthetase (NRPS) and polyketide synthase (PKS), implying the presence of new compounds with valuable activities in the mangrove swamp microbiome.

Utilization of-Omic technologies in cold climate hydrocarbon bioremediation: a text-mining approach

Hydrocarbon spills in cold climates are a prominent and enduring form of anthropogenic contamination. Bioremediation is one of a suite of remediation tools that has emerged as a cost-effective strategy for transforming these contaminants in soil, ideally into less harmful products. However, little is understood about the molecular mechanisms driving these complex, microbially mediated processes. The emergence of -omic technologies has led to a revolution within the sphere of environmental microbiology allowing for the identification and study of so called 'unculturable' organisms. In the last decade, -omic technologies have emerged as a powerful tool in filling this gap in our knowledge on the interactions between these organisms and their environment in vivo. Here, we utilize the text mining software Vosviewer to process meta-data and visualize key trends relating to cold climate bioremediation projects. The results of text mining of the literature revealed a shift over time from optimizing bioremediation experiments on the macro/community level to, in more recent years focusing on individual organisms of interest, interactions within the microbiome and the investigation of novel metabolic degradation pathways. This shift in research focus was made possible in large part by the rise of omics studies allowing research to focus not only what organisms/metabolic pathways are present but those which are functional. However, all is not harmonious, as the development of downstream analytical methods and associated processing tools have outpaced sample preparation methods, especially when dealing with the unique challenges posed when analyzing soil-based samples.

Comprehensive insights on environmental adaptation strategies in Antarctic bacteria and biotechnological applications of cold adapted molecules

Climate change and the induced environmental disturbances is one of the major threats that have a strong impact on bacterial communities in the Antarctic environment. To cope with the persistent extreme environment and inhospitable conditions, psychrophilic bacteria are thriving and displaying striking adaptive characteristics towards severe external factors including freezing temperature, sea ice, high radiation and salinity which indicates their potential in regulating climate change's environmental impacts. The review illustrates the different adaptation strategies of Antarctic microbes to changing climate factors at the structural, physiological and molecular level. Moreover, we discuss the recent developments in "omics" approaches to reveal polar "blackbox" of psychrophiles in order to gain a comprehensive picture of bacterial communities. The psychrophilic bacteria synthesize distinctive cold-adapted enzymes and molecules that have many more industrial applications than mesophilic ones in biotechnological industries. Hence, the review also emphasizes on the biotechnological potential of psychrophilic enzymes in different sectors and suggests the machine learning approach to study cold-adapted bacteria and engineering the industrially important enzymes for sustainable bioeconomy.

Novel Sources of Biodiversity and Biomolecules from Bacteria Isolated from a High Middle Ages Soil Sample in Palermo (Sicily, Italy)

The urban plan of Palermo (Sicily, Italy) has evolved throughout Punic, Roman, Byzantine, Arab, and Norman ages until it stabilized within the borders that correspond to the current historic center. During the 2012 to 2013 excavation campaign, new remains of the Arab settlement, directly implanted above the structures of the Roman age, were found. The materials investigated in this study derived from the so-called Survey No 3, which consists of a rock cavity of subcylindrical shape covered with calcarenite blocks: it was probably used to dispose of garbage during the Arabic age and its content, derived from daily activities, included grape seeds, scales and bones of fish, small animal bones, and charcoals. Radiocarbon dating confirmed the medieval origin of this site. The composition of the bacterial community was characterized through a culture-dependent and a culture-independent approach. Culturable bacteria were isolated under aerobic and anaerobic conditions and the total bacterial community was characterized through metagenomic sequencing. Bacterial isolates were tested for the production of compounds with antibiotic activity: a Streptomyces strain, whose genome was sequenced, was of particular interest because of its inhibitory activity, which was due to the Type I polyketide aureothin. Moreover, all strains were tested for the production of secreted proteases, with those belonging to the genus Nocardioides having the most active enzymes. Finally, protocols commonly used for ancient DNA studies were applied to evaluate the antiquity of isolated bacterial strains. Altogether these results show how paleomicrobiology might represent an innovative and unexplored source of novel biodiversity and new biotechnological tools. IMPORTANCE One of the goals of paleomicrobiology is the characterization of the microbial community present in archaeological sites. These analyses can usually provide valuable information about past events, such as occurrence of human and animal infectious diseases, ancient human activities, and environmental changes. However, in this work, investigations about the composition of the bacterial community of an ancient soil sample (harvested in Palermo, Italy) were carried out aiming to screen ancient culturable strains with biotechnological potential, such as the ability to produce bioactive molecules and secreted hydrolytic enzymes. Besides showing the biotechnological relevance of paleomicrobiology, this work reports a case of germination of putatively ancient bacterial spores recovered from soil rather than extreme environments. Moreover, in the case of spore-forming species, these results raise questions about the accuracy of techniques usually applied to estimate antiquity of DNA, as they could lead to its underestimation.

Metagenomics reveals the habitat specificity of biosynthetic potential of secondary metabolites in global food fermentations

BACKGROUND

Fermented foods are considered to be beneficial for human health. Secondary metabolites determined by biosynthetic gene clusters (BGCs) are precious bioactive compounds with various biological activities. However, the diversity and distribution of the biosynthetic potential of secondary metabolites in global food fermentations remain largely unknown. In this study, we performed a large-scale and comprehensive investigation for the BGCs in global food fermentations by metagenomics analysis.

RESULTS

We recovered 653 bacterial metagenome-assembled genomes (MAGs) from 367 metagenomic sequencing datasets covering 15 general food fermentation types worldwide. In total, 2334 secondary metabolite BGCs, including 1003 novel BGCs, were identified in these MAGs. Bacillaceae, Streptococcaceae, Streptomycetaceae, Brevibacteriaceae and Lactobacillaceae contained high abundances of novel BGCs (≥ 60 novel BGCs). Among 2334 BGCs, 1655 were habitat-specific, originating from habitat-specific species (80.54%) and habitat-specific genotypes within multi-habitat species (19.46%) in different food fermentation types. Biological activity analysis suggested that 183 BGC-producing secondary metabolites exhibited high probabilities of antibacterial activity (> 80%). These 183 BGCs were distributed across all 15 food fermentation types, and cheese fermentation contained the most BGC number.

CONCLUSIONS

This study demonstrates that food fermentation systems are an untapped reservoir of BGCs and bioactive secondary metabolites, and it provides novel insights into the potential human health benefits of fermented foods. Video Abstract.

Chromosomal organization of biosynthetic gene clusters suggests plasticity of myxobacterial specialized metabolism including descriptions for nine novel species: Archangium lansinium sp. nov., Myxococcus landrumus sp. nov., Nannocystis bainbridgea sp. nov., Nannocystis poenicansa sp. nov., Nannocystis radixulma sp. nov., Polyangium mundeleinium sp. nov., Pyxidicoccus parkwaysis sp. nov., Sorangium aterium sp. nov., Stigmatella ashevillena sp. nov

Natural products discovered from bacteria provide critically needed therapeutic leads for drug discovery, and myxobacteria are an established source for metabolites with unique chemical scaffolds and biological activities. Myxobacterial genomes accommodate an exceptional number and variety of biosynthetic gene clusters (BGCs) which encode for features involved in specialized metabolism. Continued discovery and sequencing of novel myxobacteria from the environment provides BGCs for the genome mining pipeline. Herein, we describe the collection, sequencing, and genome mining of 20 myxobacteria isolated from rhizospheric soil samples collected in North America. Nine isolates where determined to be novel species of myxobacteria including representatives from the genera Archangium, Myxococcus, Nannocystis, Polyangium, Pyxidicoccus, Sorangium, and Stigmatella. Growth profiles, biochemical assays, and descriptions are provided for all proposed novel species. We assess the BGC content of all isolates and observe differences between Myxococcia and Polyangiia clusters. Utilizing complete or near complete genome sequences we compare the chromosomal organization of BGCs of related myxobacteria from various genera and suggest spatial proximity of hybrid, modular clusters contributes to the metabolic adaptability of myxobacteria.

Glacier-Fed Stream Biofilms Harbor Diverse Resistomes and Biosynthetic Gene Clusters

Antimicrobial resistance (AMR) is a universal phenomenon the origins of which lay in natural ecological interactions such as competition within niches, within and between micro- to higher-order organisms. To study these phenomena, it is crucial to examine the origins of AMR in pristine environments, i.e., limited anthropogenic influences. In this context, epilithic biofilms residing in glacier-fed streams (GFSs) are an excellent model system to study diverse, intra- and inter-domain, ecological crosstalk. We assessed the resistomes of epilithic biofilms from GFSs across the Southern Alps (New Zealand) and the Caucasus (Russia) and observed that both bacteria and eukaryotes encoded twenty-nine distinct AMR categories. Of these, beta-lactam, aminoglycoside, and multidrug resistance were both abundant and taxonomically distributed in most of the bacterial and eukaryotic phyla. AMR-encoding phyla included Bacteroidota and Proteobacteria among the bacteria, alongside Ochrophyta (algae) among the eukaryotes. Additionally, biosynthetic gene clusters (BGCs) involved in the production of antibacterial compounds were identified across all phyla in the epilithic biofilms. Furthermore, we found that several bacterial genera (Flavobacterium, Polaromonas, Superphylum Patescibacteria) encode both atimicrobial resistance genes (ARGs) and BGCs within close proximity of each other, demonstrating their capacity to simultaneously influence and compete within the microbial community. Our findings help unravel how naturally occurring BGCs and AMR contribute to the epilithic biofilms mode of life in GFSs. Additionally, we report that eukaryotes may serve as AMR reservoirs owing to their potential for encoding ARGs. Importantly, these observations may be generalizable and potentially extended to other environments that may be more or less impacted by human activity. IMPORTANCE Antimicrobial resistance is an omnipresent phenomenon in the anthropogenically influenced ecosystems. However, its role in shaping microbial community dynamics in pristine environments is relatively unknown. Using metagenomics, we report the presence of antimicrobial resistance genes and their associated pathways in epilithic biofilms within glacier-fed streams. Importantly, we observe biosynthetic gene clusters associated with antimicrobial resistance in both pro- and eukaryotes in these biofilms. Understanding the role of resistance in the context of this pristine environment and complex biodiversity may shed light on previously uncharacterized mechanisms of cross-domain interactions.

A Genomic Survey of the Natural Product Biosynthetic Potential of Actinomycetes Isolated from New Zealand Lichens

Actinomycetes are prolific producers of industrially valuable and medically important compounds. Historically, the most efficient method of obtaining compounds has been bioactivity-guided isolation and characterization of drug-like molecules from culturable soil actinomycetes. Unfortunately, this pipeline has been met with an increasing number of rediscoveries, to the point where it is no longer considered an attractive approach for drug discovery. To address this challenge and to continue finding new compounds, researchers have increasingly focused on alternative environmental niches and screening methods. Here, we report the genetic investigation of actinomycetes from an underexplored source, New Zealand lichens. In this work, we obtain draft genome sequences for 322 lichen-associated actinomycetes. We then explore this genetic resource with an emphasis on biosynthetic potential. By enumerating biosynthetic gene clusters (BGCs) in our data sets and comparing these to various reference collections, we demonstrate that actinomycetes sourced from New Zealand lichens have the genetic capacity to produce large numbers of natural products, many of which are expected to be broadly different from those identified in previous efforts predominantly based on soil samples. Our data shed light on the actinomycete assemblage in New Zealand lichens and demonstrate that lichen-sourced actinobacteria could serve as reservoirs for discovering new secondary metabolites. IMPORTANCE Lichens are home to complex and distinctive microbial cohorts that have not been extensively explored for the ability to produce novel secondary metabolites. Here, we isolate and obtain genome sequence data for 322 actinomycetes from New Zealand lichens. In doing so, we delineate at least 85 potentially undescribed species, and show that lichen associated actinomycetes have the potential to yield many new secondary metabolites, and as such, might serve as a productive starting point for drug discovery efforts.

Effect of dietary biochanin A on lactation performance, antioxidant capacity, rumen fermentation and rumen microbiome of dairy goat

Biochanin A (BCA), an isoflavone phytoestrogen, is a secondary metabolite produced mainly in leguminous plants. The objective of this study was to evaluate the effect of BCA on lactation performance, nitrogen metabolism, and the health of dairy goat. Thirty mid-lactation Saanen dairy goats were divided into three groups randomly: control, 2 g/d BCA group, and 6 g/d BCA group. After 36 days of feeding, 30 dairy goats were transferred to individual metabolic cages. Subsequently, milk yield, feed intake, total feces, and urine excretion were recorded and samples were collected continuously for 3 days. Blood and ruminal fluid samples were collected over the subsequent 4 days. Milk yield, milk protein, fat content, and the feed conversion ratio of dairy goat were significantly increased by the BCA treatment. The levels of serum 17β-estradiol, growth hormone, insulin-like growth factor 1, glutathione peroxidase activity, and total antioxidant capacity were also increased significantly by BCA, indicating that BCA enhanced the antioxidant capacity of dairy goat. Amino acid degradation was significantly inhibited, while the ammonia nitrogen content was reduced significantly by BCA. Total volatile fatty acids was significantly increased by BCA supplementation. In addition, the relative abundance of Verrucomicrobiota was decreased significantly. However, the growth of nitrogen metabolism and cellulolytic bacteria was significantly increased under BCA treatment, including Prevotella sp., Treponema sp., Ruminococcus flavefaciens, and Ruminobacter amylophilus. In conclusion, supplementation with BCA improved the milk production performance, nitrogen metabolism, rumen fermentation and antioxidant capacity, and regulated the rumen microbiome of dairy goat.

Strategies and tools in illumina and nanopore-integrated metagenomic analysis of microbiome data

Metagenomic strategy serves as the foundation for the ecological exploration of novel bioresources (e.g., industrial enzymes and bioactive molecules) and biohazards (e.g., pathogens and antibiotic resistance genes) in natural and engineered microbial systems across multiple disciplines. Recent advancements in sequencing technology have fostered rapid development in the field of microbiome research where an increasing number of studies have applied both illumina short reads (SRs) and nanopore long reads (LRs) sequencing in their metagenomic workflow. However, given the high complexity of an environmental microbiome data set and the bioinformatic challenges caused by the unique features of these sequencing technologies, integrating SRs and LRs is not as straightforward as one might assume. The fast renewal of existing tools and growing diversity of new algorithms make access to this field even more difficult. Therefore, here we systematically summarized the complete workflow from DNA extraction to data processing strategies for applying illumina and nanopore-integrated metagenomics in the investigation in environmental microbiomes. Overall, this review aims to provide a timely knowledge framework for researchers that are interested in or are struggling with the SRs and LRs integration in their metagenomic analysis. The discussions presented will facilitate improved ecological understanding of community functionalities and assembly of natural, engineered, and human microbiomes, benefiting researchers from multiple disciplines.

Green Manures Alter Taxonomic and Functional Characteristics of Soil Bacterial Communities

Incorporation of plant biomass into soil as green manures can reduce soilborne diseases and improve crop and soil health in agricultural ecosystems. Soil microbial communities can mediate beneficial effects of these amendments, but their response to different types of green manures is poorly understood. This study tested the effect of green manures from broccoli, marigold, and sudangrass on taxonomic and functional characteristics of soil bacterial communities. Green manures were amended to field soil and maintained in microcosms artificially infested with the soilborne plant pathogen Verticillium dahliae. Lettuce seedlings were transplanted into green manure amended and fallow soil and maintained under growth chamber conditions for 12 weeks. Bacterial communities in bulk and rhizosphere soils were characterized using nanopore sequencing of 16S rRNA and shotgun metagenome libraries. Under microcosm conditions, all green manures reduced the abundance of the soilborne plant pathogen V. dahliae and altered the taxonomic composition of bacterial communities. Twelve weeks following amendment, green manures had differential effects on lettuce yield as well as the taxonomic diversity and composition of soil bacterial communities. In addition, multiple green manures increased the abundance of bacterial functional traits in rhizosphere soil related to iron and polysaccharide acquisition and decreased the abundance of functional traits related to bacterial protein secretion systems. This study demonstrates green manures alter the taxonomic composition and functional traits in soil bacterial communities suggesting these changes may impact beneficial effects of green manures on plant and soil health.

Identification of PKS Gene Clusters from Metagenomic Libraries Using a Next-Generation Sequencing Approach

Microbial secondary metabolites have been an important source of bioactive compounds with diverse applications from medicine to agriculture, noticeably those encoded by polyketide synthase (PKS) clusters due to their astounding chemical diversity. While most discovered compounds originate from culturable microorganisms, yet-to-be cultured microbes represent a reservoir of previously inaccessible compounds. The advent and development of metagenomics have allowed not only the characterization of these microorganisms but also their metabolic potential, making viable the prospection of environmental PKS for natural product discovery.Study of environmental PKSs often relies on the construction of metagenomic libraries and their mining, with clones containing PKS clusters identified via amplification of conserved domains and then screened for an activity of interest. Compounds produced by clones exhibiting the desired bioactivity can be isolated and characterized. However, these approaches can be less sensitive and biased against more divergent clusters, in addition to precluding the use of bioinformatics for cluster characterization prior to expression. While direct shotgun sequencing of metagenomes has identified and profiled a great number of PKSs from different environments and yet-to-be cultured microorganisms, it does not lend itself well to heterologous expression, the cruxes of natural product discovery.Here, we describe a strategy for sequencing entire metagenomic libraries while maintaining correspondence between sequence and clone, allowing the full characterization and annotation of all clusters present in a library using bioinformatic tools and then seamlessly passing clones of interest for activity screening through heterologous expression. Once a library is sequenced, the methods herein can be adapted for the mining of any biosynthetic gene cluster of interest within a metagenomic library.