CRISPRCasTyper: Automated Identification, Annotation, and Classification of CRISPR-Cas Loci

Biogeographic patterns of viral communities, ARG profiles and virus-ARG associations in adjacent paddy and upland soils across black soil region

Biogeographic distribution of prokaryotic and eukaryotic communities has been extensively studied. Yet, our knowledge of viral biogeographic patterns, the corresponding driving factors and the virus-resistome associations is still limited. Here, using metagenomic analysis, we explored the viral communities and profiles of antibiotic resistance genes (ARGs) in 30 fields of paddy (rice soils, RS) and upland soils (corn soils, CS) at a regional scale across black soil region of Northeast China. Our finding revealed that viral communities displayed significant distance-decay relationships, and environmental variables largely dominated viral community patterns in agricultural soils. Compared to RS, viral community in CS harbored significantly higher viral α-diversity and distinct β-diversity, and exhibited a higher turnover along with environmental gradients and spatial distance. However, no clear latitudinal diversity gradient (LDG) pattern was observed in viral diversity over large-scale sampling for RS and CS, and heterogeneous distribution of soil viruses was well maintained over large-scale sampling. Soil pH was the important influential factor driving viral community, and the high soil nutrient levels negatively affected viral diversity. Uroviricota, Nucleocytoviricota and Artverviricota were the main viral phyla in agricultural soils, and virus-host linkages spanned 17 prokaryotic phyla, including Actinobacteriota and Proteobacteria. Besides, 2578 ARG subtypes were retrieved and conferred resistance to 27 types of antibiotics, in which multidrug was the predominant ARG type in Mollisols. Procrustes analysis showed the significant contribution of viral community to ARG profiles, which was more obvious in CS compared to RS. We identified 9.61 % and 11.4 % of soil viruses carried at least one ARG can infect multi-host in RS and CS. Furthermore, 43 and 77 complete viral metagenome-assembled genome (vMAG) were reconstructed in RS and CS, respectively. Notably, the lysogenic phages in RS contained 29.7 % of ARGs, a higher proportion than the 12.5 % found in CS. Overall, our study underscored the prevalent distribution of viral communities and ARG profiles at a large spatial scale, and the distinct ecological strategies of virus-ARG associations in adjacent paddy and upland soils.

Global emergence of Carbapenem-resistant Hypervirulent Klebsiella pneumoniae driven by an IncFIIK34 KPC-2 plasmid

BACKGROUND

Carbapenem-resistant hypervirulent Klebsiella pneumoniae (CR-hvKp) has been increasingly reported worldwide, posing a severe challenge to public health; however, the mechanisms driving its emergence and global dissemination remain unclear.

METHODS

We analysed CR-hvKp strains derived from canonical hvKp backgrounds, and acquired a carbapenemase-encoding gene. These strains were identified from 485 CRKp isolates in the CRACKLE-2 China cohort, 259 CRKp isolates from a multi-centre study, and 67,631 K. pneumoniae genomes available in GenBank. Clinical isolates harbouring the IncFIIK34 KPC-2 plasmid were selected for genome sequencing, RNA-Seq, conjugation assays, in vivo, ex vivo, and in vitro phenotypic characterisation.

FINDINGS

Analysis of clinical CR-hvKp isolates and the 414 genomes from 24 countries available in GenBank identified an IncFIIK34 KPC-2 plasmid as the prevalent KPC plasmid (detected in 25%, 45/178 of KPC-producing CR-hvKp). Compared with the epidemic IncFIIK2 KPC-2 plasmid, the IncFIIK34 KPC-2 plasmid exhibited a 100- to 1000-fold increase in conjugation frequency (10-4-10-5 vs. 10-7) and an in vitro growth advantage under meropenem challenge-likely due to the overexpression of conjugation-related genes and an increased blaKPC copy number and expression. CR-hvKp isolates and hvKp transconjugants carrying this plasmid often exhibited reduced mucoviscosity, while retaining hypervirulence in both murine models and human neutrophil assays.

INTERPRETATION

The IncFIIK34 plasmid may be a key factor driving the global dissemination of CR-hvKp, underscoring the urgent need for enhanced molecular surveillance of this emerging pathogen.

FUNDING

National Natural Science Foundation of China and National Institutes of Health.

Engineering a New Generation of Gene Editors: Integrating Synthetic Biology and AI Innovations

CRISPR-Cas technology has revolutionized biology by enabling precise DNA and RNA edits with ease. However, significant challenges remain for translating this technology into clinical applications. Traditional protein engineering methods, such as rational design, mutagenesis screens, and directed evolution, have been used to address issues like low efficacy, specificity, and high immunogenicity. These methods are labor-intensive, time-consuming, and resource-intensive and often require detailed structural knowledge. Recently, computational strategies have emerged as powerful solutions to these limitations. Using artificial intelligence (AI) and machine learning (ML), the discovery and design of novel gene-editing enzymes can be streamlined. AI/ML models predict activity, specificity, and immunogenicity while also enhancing mutagenesis screens and directed evolution. These approaches not only accelerate rational design but also create new opportunities for developing safer and more efficient genome-editing tools, which could eventually be translated into the clinic.

Antiviral defense systems in the rumen microbiome

The continuous interaction between phages and their respective hosts has resulted in the evolution of multiple bacterial immune mechanisms. However, the diversity and prevalence of antiviral defense systems in complex communities are still unknown. We therefore investigated the diversity and abundance of viral defense systems in 3,038 high-quality bacterial and archaeal genomes from the rumen. In total, 14,241 defense systems and 31,948 antiviral-related genes were identified. Those genes represented 114 unique system types grouped into 49 families. We observed a high prevalence of defense systems in the genomes. However, the number of defense systems, defense system families, and system density varied widely from genome to genome. Additionally, the number of defense system per genome correlated positively with the number of defense system families and the genome size. Restriction modification, Abi, and cas system families were the most common, but many rare systems were present in only 1% of the genomes. Antiviral defense systems are prevalent and diverse in the rumen, but only a few are dominant, indicating that most systems are rarely present. However, the collection of systems throughout the rumen may represent a pool of mechanisms that can be shared by different members of the community and modulate the phage-host interaction.IMPORTANCEPhages may act antagonistically at the cell level but have a mutualistic interaction at the microbiome level. This interaction shapes the structure of microbial communities and is mainly driven by the defense mechanism. However, the diversity of such mechanism is larger than previously thought. Because of that, we described the abundance and diversity of the antiviral defense system of a collection of genomes, metagenome-assembled genomes (MAGs) and isolates, from the rumen. While defense mechanisms seem to be prevalent among bacteria and archaea, only a few were common. This suggests that most of these defense mechanisms are not present in many rumen microbes but could be shared among different members of the microbial community. This is consistent with the "pan-immune system" model, which appears to be common across different environments.

Transitioning from wet lab to artificial intelligence: a systematic review of AI predictors in CRISPR

The revolutionary CRISPR-Cas9 system leverages a programmable guide RNA (gRNA) and Cas9 proteins to precisely cleave problematic regions within DNA sequences. This groundbreaking technology holds immense potential for the development of targeted therapies for a wide range of diseases, including cancers, genetic disorders, and hereditary diseases. CRISPR-Cas9 based genome editing is a multi-step process such as designing a precise gRNA, selecting the appropriate Cas protein, and thoroughly evaluating both on-target and off-target activity of the Cas9-gRNA complex. To ensure the accuracy and effectiveness of CRISPR-Cas9 system, after the targeted DNA cleavage, the process requires careful analysis of the resultant outcomes such as indels and deletions. Following the success of artificial intelligence (AI) in various fields, researchers are now leveraging AI algorithms to catalyze and optimize the multi-step process of CRISPR-Cas9 system. To achieve this goal AI-driven applications are being integrated into each step, but existing AI predictors have limited performance and many steps still rely on expensive and time-consuming wet-lab experiments. The primary reason behind low performance of AI predictors is the gap between CRISPR and AI fields. Effective integration of AI into multi-step CRISPR-Cas9 system demands comprehensive knowledge of both domains. This paper bridges the knowledge gap between AI and CRISPR-Cas9 research. It offers a unique platform for AI researchers to grasp deep understanding of the biological foundations behind each step in the CRISPR-Cas9 multi-step process. Furthermore, it provides details of 80 available CRISPR-Cas9 system-related datasets that can be utilized to develop AI-driven applications. Within the landscape of AI predictors in CRISPR-Cas9 multi-step process, it provides insights of representation learning methods, machine and deep learning methods trends, and performance values of existing 50 predictive pipelines. In the context of representation learning methods and classifiers/regressors, a thorough analysis of existing predictive pipelines is utilized for recommendations to develop more robust and precise predictive pipelines.

Isolation of Enterococcus hirae From Fresh White Yak Milk in Ledu District, Qinghai Province, China: A Comparative Genomic Analysis

Yak milk is a widely consumed dairy product rich in lactic acid bacteria. Although Enterococcus hirae (E. hirae) is commonly found in dairy products and other foods, there is limited information available on its genetic makeup in yak milk. In the present study, 10 E. hirae strains isolated and identified from fresh white yak milk samples, along with 442 E. hirae strains obtained from the NCBI database (totaling 452 strains), were subjected to comparative genomic analysis. The findings of this study revealed that E. hirae has an open pan-genomic structure that allows for its high adaptability and environmental plasticity. Notably, E. hirae isolates from fresh white yak milk had smaller genomes, encoded more functional genes, and had fewer copies of genes encoding carbohydrate-active enzymes involved in the degradation of oligosaccharide metabolism and autolysin synthesis (CE1, GH73, GH23, and GT4 families) than those from animal and human isolates (P < 0.05). Additionally, fresh white yak milk isolates carried only three intrinsic bacteriocins and lacked virulence factors, CRISPR-Cas systems, and resistance genes linked to pathogenicity, which may be attributed to their specialization in the milk-derived environment. This study provides new insights into the genetic and functional gene diversity of E. hirae and how it adapts to milk-derived habitats.

Relationship Between CRISPR-Cas Systems and Acquisition of Tetracycline Resistance in Non-Clinical Enterococcus Populations in Bulgaria

Non-clinical enterococci are relatively poorly studied by means of acquired antibiotic resistance to tetracycline and by the distribution, functionality and role of their CRISPR systems. Background: In our study, 72 enterococcal strains, isolated from various non-clinical origins, were investigated for their phenotypic and genotypic (tet(M), tet(O), tet(S), tet(L), tet(K), tet(T) and tet(W)) tetracycline resistance. Methods: The genetic determinants for HGT (MGEs (Int-Tn and prgW), inducible pheromones (cpd, cop and cff), aggregation substances (agg, asa1, prgB and asa373) and CRISPR-Cas systems were characterized by PCR and whole-genome sequencing. Results: Four tet genes (tetM, tetO, tetS and tetT) were detected in 39% (n = 28) of our enterococcal population, with tetM (31%) being dominant. The gene location was linked to the Tn6009 transposon. All strains that contained tet genes also had genes for HGT. No tet genes were found in E. casseliflavus and E. gilvus. In our study, 79% of all tet-positive strains correlated with non-functional CRISPR systems. The strain E. faecalis BM15 was the only one containing a combination of a functional CRISPR system (cas1, cas2, csn2 and csn1/cas9) and tet genes. The CRISPR subtype repeats II-A, III-B, IV-A2 and VI-B1 were identified among E. faecalis strains (CM4-II-A, III-B and VI-B1; BM5-IV-A2, II-A and III-B; BM12 and BM15-II-A). The subtype II-A was the most present. These repeats enclosed a great number of spacers (1-10 spacers) with lengths of 31 to 36 bp. One CRISPR locus was identified in plasmid (p.Firmicutes1 in strain E. faecalis BM5). We described the presence of CRISPR loci in the species E. pseudoavium, E. pallens and E. devriesei and their lack in E. gilvus, E. malodoratus and E. mundtii. Conclusions: Our findings generally describe the acquisition of foreign DNA as a consequence of CRISPR inactivation, and self-targeting spacers as the main cause.

Adaptive modification of antiviral defense systems in microbial community under Cr-induced stress

BACKGROUND

The prokaryotic antiviral defense systems are crucial for mediating prokaryote-virus interactions that influence microbiome functioning and evolutionary dynamics. Despite the prevalence and significance of prokaryotic antiviral defense systems, their responses to abiotic stress and ecological consequences remain poorly understood in soil ecosystems. We established microcosm systems with varying concentrations of hexavalent chromium (Cr(VI)) to investigate the adaptive modifications of prokaryotic antiviral defense systems under abiotic stress.

RESULTS

Utilizing hybrid metagenomic assembly with long-read and short-read sequencing, we discovered that antiviral defense systems were more diverse and prevalent in heavily polluted soils, which was corroborated by meta-analyses of public datasets from various heavy metal-contaminated sites. As the Cr(VI) concentration increased, prokaryotes with defense systems favoring prokaryote-virus mutualism gradually supplanted those with defense systems incurring high adaptive costs. Additionally, as Cr(VI) concentrations increased, enriched antiviral defense systems exhibited synchronization with microbial heavy metal resistance genes. Furthermore, the proportion of antiviral defense systems carried by mobile genetic elements (MGEs), including plasmids and viruses, increased by approximately 43% and 39%, respectively, with rising Cr concentrations. This trend is conducive to strengthening the dissemination and sharing of defense resources within microbial communities.

CONCLUSIONS

Overall, our study reveals the adaptive modification of prokaryotic antiviral defense systems in soil ecosystems under abiotic stress, as well as their positive contributions to establishing prokaryote-virus mutualism and the evolution of microbial heavy metal resistance. These findings advance our understanding of microbial adaptation in stressful environments and may inspire novel approaches for microbiome manipulation and bioremediation. Video Abstract.

Intricate interplay of CRISPR-Cas systems, anti-CRISPR proteins, and antimicrobial resistance genes in a globally successful multi-drug resistant Klebsiella pneumoniae clone

BACKGROUND

Klebsiella pneumoniae is one of the most prevalent pathogens responsible for multiple infections in healthcare settings and the community. K. pneumoniae CG147, primarily including ST147 (the founder ST), ST273, and ST392, is one of the most globally successful MDR clone linked to various carbapenemases.

METHODS

One hundred and one CG147 strains were sequenced and additional 911 publicly available CG147 genome sequences were included for analysis. The molecular epidemiology, population structure, and time phylogeny were investigated. The virulome, resistome, and mobilome were analyzed, and the recombination in the capsular region was studied. The CRISPR-Cas and anti-CRISPR were identified. The interplay between CRISPR-Cas, anti-CRISPR, and carbapenemase-encoding plasmids was analyzed and experimentally validated.

RESULTS

We analyzed 1012 global CG147 genomes, with 80.4% encoding at least one carbapenemase (NDM [529/1012, 52.3%], OXA-48-like [182/1012, 17.7%], and KPC [105/1012, 10.4%]). Surprisingly, almost all CG147 strains (99.7%, 1009/1,012) harbor a chromosomal type I-E CRISPR-Cas system, with 41.8% (423/1012) containing an additional plasmid-borne type IV-A3 CRISPR-Cas system, and both target IncF plasmids, e.g., the most prevalent KPC-encoding pKpQIL-like plasmids. We found the presence of IV-A3 CRISPR-Cas system showed a negative correlation with the presence of KPC. Interestingly, a prophage-encoding anti-CRISPR AcrIE8.1 and a plasmid-borne anti-CRISPR AcrIE9.2 were detected in 40.1% (406/1012) and 54.2% (548/1012) of strains, respectively, which displayed positive correlations with the presence of a carbapenemase. Plasmid transfer experiments confirmed that the I-E and IV-A3 CRISPR-Cas systems significantly decreased (p < 0.001) KPC-encoding pKpQIL plasmid conjugation frequencies, while the AcrIE8.1 and AcrIE9.2 significantly increased (p < 0.001) pKpQIL conjugation frequencies and protected plasmids from elimination by CRISPR-Cas I-E system.

CONCLUSIONS

Our results indicated a complex interplay between CRISPR-Cas, anti-CRISPR, and mobile genetic elements that shape the evolution of CG147. Our findings advance the understanding of multi-drug resistance mechanisms and will aid in preventing the emergence of future MDR clones.

Pseudomonas aeruginosa maintains an inducible array of novel and diverse prophages over lengthy persistence in cystic fibrosis lungs

Pseudomonas aeruginosa has increasing clinical relevance and commonly occupies the cystic fibrosis (CF) airways. Its ability to colonize and persist in diverse niches is attributed to its large accessory genome, where prophages represent a common feature and may contribute to its fitness and persistence. We focused on the CF airways niche and used 197 longitudinal isolates from 12 patients persistently infected by P. aeruginosa. We computationally predicted intact prophages for each longitudinal group and scored their long-term persistence. We then confirmed prophage inducibility and mapped their location in the host chromosome with lysate sequencing. Using comparative genomics, we evaluated prophage genomic diversity, long-term persistence, and level of genomic maintenance. Our findings support previous findings that most P. aeruginosa genomes harbour prophages some of which can self-induce, and that a common CF-treating antibiotic, ciprofloxacin, can induce prophages. Induced prophage genomes displayed high diversity and even genomic novelty. Finally, all induced prophages persisted long-term with their genomes avoiding gene loss and degradation over 4 years of host replication in the stressful CF airways niche. This and our detection of phage genes, which contribute to host competitiveness and adaptation, lends support to our hypothesis that the vast majority of prophages detected as intact and inducible in this study facilitated their host fitness and persistence.

CRISPR-Cas spacer acquisition is a rare event in human gut microbiome

Host-parasite relationships drive the evolution of both parties. In microbe-phage dynamics, CRISPR functions as an adaptive defense mechanism, updating immunity via spacer acquisition. Here, we investigated these interactions within the human gut microbiome, uncovering low frequencies of spacer acquisition at an average rate of one spacer every ∼2.9 point mutations using isolates' whole genomes and ∼2.7 years using metagenome time series. We identified a highly prevalent CRISPR array in Bifidobacterium longum spreading via horizontal gene transfer (HGT), with six spacers found in various genomic regions in 15 persons from the United States and Europe. These spacers, targeting two prominent Bifidobacterium phages, comprised 76% of spacer occurrence of all spacers targeting these phages in all B. longum populations. This result suggests that HGT of an entire CRISPR-Cas system introduced three times more spacers than local CRISPR-Cas acquisition in B. longum. Overall, our findings identified key ecological and evolutionary factors in prokaryote adaptive immunity.

PlasmidScope: a comprehensive plasmid database with rich annotations and online analytical tools

Plasmids are extrachromosomal genetic molecules that replicate independent of chromosomes in bacteria, archaea, and eukaryotic organisms. They contain diverse functional elements and are capable of horizontal gene transfer among hosts. While existing plasmid databases have archived plasmid sequences isolated from individual microorganisms or natural environments, there is a need for a comprehensive, standardized, and annotated plasmid database to address the vast accumulation of plasmid sequences. Here, we propose PlasmidScope (https://plasmid.deepomics.org/), a plasmid database offering comprehensive annotations, automated online analysis, and interactive visualization. PlasmidScope harbors a substantial collection of 852 600 plasmids curated from 10 repositories. Along with consolidated background information, PlasmidScope utilizes 12 state-of-the-art tools and provides comprehensive annotations for the curated plasmids, covering genome completeness, topological structure, mobility, host source, tRNA, tmRNA, signal peptides, transmembrane proteins and CRISPR/Cas systems. PlasmidScope offers diverse functional annotations for its 25 231 059 predicted genes from 9 databases as well as corresponding protein structures predicted by ESMFold. In addition, PlasmidScope integrates online analytical modules and interactive visualization, empowering researchers to delve into the complexities of plasmids.

Engineering of CRISPR-Cas PAM recognition using deep learning of vast evolutionary data

CRISPR-Cas enzymes must recognize a protospacer-adjacent motif (PAM) to edit a genomic site, significantly limiting the range of targetable sequences in a genome. Machine learning-based protein engineering provides a powerful solution to efficiently generate Cas protein variants tailored to recognize specific PAMs. Here, we present Protein2PAM, an evolution-informed deep learning model trained on a dataset of over 45,000 CRISPR-Cas PAMs. Protein2PAM rapidly and accurately predicts PAM specificity directly from Cas proteins across Type I, II, and V CRISPR-Cas systems. Using in silico deep mutational scanning, we demonstrate that the model can identify residues critical for PAM recognition in Cas9 without utilizing structural information. As a proof of concept for protein engineering, we employ Protein2PAM to computationally evolve Nme1Cas9, generating variants with broadened PAM recognition and up to a 50-fold increase in PAM cleavage rates compared to the wild-type under in vitro conditions. This work represents the first successful application of machine learning to achieve customization of Cas enzymes for alternate PAM recognition, paving the way for personalized genome editing.

An ecological-evolutionary perspective on the genomic diversity and habitat preferences of the Acidobacteriota

Members of the phylum Acidobacteriota inhabit a wide range of ecosystems including soils. We analysed the global patterns of distribution and habitat preferences of various Acidobacteriota lineages across major ecosystems (soil, engineered, host-associated, marine, non-marine saline and alkaline and terrestrial non-soil ecosystems) in 248 559 publicly available metagenomic datasets. Classes Terriglobia, Vicinamibacteria, Blastocatellia and Thermoanaerobaculia were highly ubiquitous and showed a clear preference to soil over non-soil habitats, while classes Aminicenantia and Holophagae showed preferences to non-soil habitats. However, while specific preferences were observed, most Acidobacteriota lineages were habitat generalists rather than specialists, with genomic and/or metagenomic fragments recovered from soil and non-soil habitats at various levels of taxonomic resolution. Comparative analysis of 1930 genomes strongly indicates that phylogenetic affiliation plays a more important role than the habitat from which the genome was recovered in shaping the genomic characteristics and metabolic capacities of the Acidobacteriota. The observed lack of strong habitat specialization and habitat-transition-driven lineage evolution in the Acidobacteriota suggest ready cross-colonization between soil and non-soil habitats. We posit that such capacity is key to the successful establishment of Acidobacteriota as a major component in soil microbiomes post-ecosystem disturbance events or during pedogenesis.

Unveiling the endogenous CRISPR-Cas system in Pseudomonas aeruginosa PAO1

Multidrug resistance in Pseudomonas aeruginosa, a high-priority pathogen per the World Health Organization, poses a global threat due to carbapenem resistance and limited antibiotic treatments. Using the bioinformatic tools CRISPRCasFinder, CRISPRCasTyper, CRISPRloci, and CRISPRImmunity, we analyzed the genome of P. aeruginosa PAO1 and revealed an orphan CRISPR system, suggesting it may be a remnant of a type IV system due to the presence of the DinG protein. This system comprises two CRISPR arrays and noteworthy DinG and Cas3 proteins, supporting recent evidence about the association between type IV and I CRISPR systems. Additionally, we demonstrated a co-evolutionary relationship between the orphan CRISPR system in P. aeruginosa PAO1 and the mobile genetic element and prophages identified. One self-targeting spacer was identified, often associated with bacterial evolution and autoimmunity, and no Acr proteins. This research opens avenues for studying how these CRISPR arrays regulate pathogenicity and for developing alternative strategies using its endogenous orphan CRISPR system against carbapenem-resistant P. aeruginosa strains.

Genomic Characterization of Probiotic Purple Nonsulfur Bacteria Cereibacter sphaeroides Strains S3W10 and SS15: Implications for Enhanced Shrimp Aquaculture

Cereibacter sphaeroides strains S3W10 and SS15, isolated from shrimp ponds, exhibit potential probiotic benefits for aquaculture. In this study, the genomic features of S3W10 and SS15 were thoroughly characterized to evaluate their probiotic properties and safety for aquaculture use. The genomes of S3W10 and SS15 consist of 130 and 74 contigs, with sizes of 4.6 Mb and 4.4 Mb and GC contents of 69.2%. Average nucleotide identity (ANI), digital DNA-DNA hybridization (dDDH), and phylogenomic analyses confirmed that these strains belong to C. sphaeroides. Genome annotation predicted 4260 coding sequences (CDS) in S3W10 and 4086 CDS in SS15, including genes associated with stress tolerance, nutrient absorption, and antioxidant activity. Notably, genes related to vitamin B12 synthesis, digestive enzyme production, and carotenoid biosynthesis, which support shrimp health, were identified in both genomes. CAZyme analysis identified 116 and 115 carbohydrate-active enzymes in S3W10 and SS15, respectively, supporting adaptation to gastrointestinal environments and the host immune response. Pan-genome analysis across C. sphaeroides strains revealed 7918 gene clusters, highlighting the open pan-genome structure of this species and its high genetic diversity. Further bioinformatic analyses assessing mobile genetic elements, antibiotic-resistance genes, and virulence factors demonstrated the safety of both strains for aquaculture, as no plasmids or virulence genes were identified. The genomic insights in this study provide a deeper understanding of the strains' adaptability and functional potential, aligning with previous in vitro and in vivo studies and highlighting their potential for use in shrimp cultivation.

The CRISPR-associated adenosine deaminase Cad1 converts ATP to ITP to provide antiviral immunity

Type III CRISPR systems provide immunity against genetic invaders through the production of cyclic oligo-adenylate (cAn) molecules that activate effector proteins that contain CRISPR-associated Rossman fold (CARF) domains. Here, we characterized the function and structure of an effector in which the CARF domain is fused to an adenosine deaminase domain, CRISPR-associated adenosine deaminase 1 (Cad1). We show that upon binding of cA4 or cA6 to its CARF domain, Cad1 converts ATP to ITP, both in vivo and in vitro. Cryoelectron microscopy (cryo-EM) structural studies on full-length Cad1 reveal an hexameric assembly composed of a trimer of dimers, with bound ATP at inter-domain sites required for activity and ATP/ITP within deaminase active sites. Upon synthesis of cAn during phage infection, Cad1 activation leads to a growth arrest of the host that prevents viral propagation. Our findings reveal that CRISPR-Cas systems employ a wide range of molecular mechanisms beyond nucleic acid degradation to provide adaptive immunity in prokaryotes.

Metagenomic characterization of viruses and mobile genetic elements associated with the DPANN archaeal superphylum

The archaeal superphylum DPANN (an acronym formed from the initials of the first five phyla discovered: Diapherotrites, Parvarchaeota, Aenigmarchaeota, Nanohaloarchaeota and Nanoarchaeota) is a group of ultrasmall symbionts able to survive in extreme ecosystems. The diversity and dynamics between DPANN archaea and their virome remain largely unknown. Here we use a metagenomic clustered regularly interspaced short palindromic repeats (CRISPR) screening approach to identify 97 globally distributed, non-redundant viruses and unclassified mobile genetic elements predicted to infect hosts across 8 DPANN phyla, including 7 viral groups not previously characterized. Genomic analysis suggests a diversity of viral morphologies including head-tailed, tailless icosahedral and spindle-shaped viruses with the potential to establish lytic, chronic or lysogenic infections. We also find evidence of a virally encoded Cas12f1 protein (probably originating from uncultured DPANN archaea) and a mini-CRISPR array, which could play a role in modulating host metabolism. Many metagenomes have virus-to-host ratios >10, indicating that DPANN viruses play an important role in controlling host populations. Overall, our study illuminates the underexplored diversity, functional repertoires and host interactions of the DPANN virome.

Expanded genome and proteome reallocation in a novel, robust Bacillus coagulans strain capable of utilizing pentose and hexose sugars

Bacillus coagulans, a Gram-positive thermophilic bacterium, is recognized for its probiotic properties and recent development as a microbial cell factory. Despite its importance for biotechnological applications, the current understanding of B. coagulans' robustness is limited, especially for undomesticated strains. To fill this knowledge gap, we characterized the metabolic capability and performed functional genomics and systems analysis of a novel, robust strain, B. coagulans B-768. Genome sequencing revealed that B-768 has the largest B. coagulans genome known to date (3.94 Mbp), about 0.63 Mbp larger than the average genome of sequenced B. coagulans strains, with expanded carbohydrate metabolism and mobilome. Functional genomics identified a well-equipped genetic portfolio for utilizing a wide range of C5 (xylose, arabinose), C6 (glucose, mannose, galactose), and C12 (cellobiose) sugars present in biomass hydrolysates, which was validated experimentally. For growth on individual xylose and glucose, the dominant sugars in biomass hydrolysates, B-768 exhibited distinct phenotypes and proteome profiles. Faster growth and glucose uptake rates resulted in lactate overflow metabolism, which makes B. coagulans a lactate overproducer; however, slower growth and xylose uptake diminished overflow metabolism due to the high energy demand for sugar assimilation. Carbohydrate Transport and Metabolism (COG-G), Translation (COG-J), and Energy Conversion and Production (COG-C) made up 60%-65% of the measured proteomes but were allocated differently when growing on xylose and glucose. The trade-off in proteome reallocation, with high investment in COG-C over COG-G, explains the xylose growth phenotype with significant upregulation of xylose metabolism, pyruvate metabolism, and tricarboxylic acid (TCA) cycle. Strain B-768 tolerates and effectively utilizes inhibitory biomass hydrolysates containing mixed sugars and exhibits hierarchical sugar utilization with glucose as the preferential substrate.IMPORTANCEThe robustness of B. coagulans makes it a valuable microorganism for biotechnology applications; yet, this phenotype is not well understood at the cellular level. Through phenotypic characterization and systems analysis, this study elucidates the functional genomics and robustness of a novel, undomesticated strain, B. coagulans B-768, capable of utilizing inhibitory switchgrass biomass hydrolysates. The genome of B-768, enriched with carbohydrate metabolism genes, demonstrates high regulatory capacity. The coordination of proteome reallocation in Carbohydrate Transport and Metabolism (COG-G), Translation (COG-J), and Energy Conversion and Production (COG-C) is critical for effective cell growth, sugar utilization, and lactate production via overflow metabolism. Overall, B-768 is a novel, robust, and promising B. coagulans strain that can be harnessed as a microbial biomanufacturing platform to produce chemicals and fuels from biomass hydrolysates.

Discovering CRISPR-Cas system with self-processing pre-crRNA capability by foundation models

The discovery of CRISPR-Cas systems has paved the way for advanced gene editing tools. However, traditional Cas discovery methods relying on sequence similarity may miss distant homologs and aren't suitable for functional recognition. With protein large language models (LLMs) evolving, there is potential for Cas system modeling without extensive training data. Here, we introduce CHOOSER (Cas HOmlog Observing and SElf-processing scReening), an AI framework for alignment-free discovery of CRISPR-Cas systems with self-processing pre-crRNA capability using protein foundation models. By using CHOOSER, we identify 11 Casλ homologs, nearly doubling the known catalog. Notably, one homolog, EphcCasλ, is experimentally validated for self-processing pre-crRNA, DNA cleavage, and trans-cleavage, showing promise for CRISPR-based pathogen detection. This study highlights an innovative approach for discovering CRISPR-Cas systems with specific functions, emphasizing their potential in gene editing.

Sequence modeling and design from molecular to genome scale with Evo

The genome is a sequence that encodes the DNA, RNA, and proteins that orchestrate an organism's function. We present Evo, a long-context genomic foundation model with a frontier architecture trained on millions of prokaryotic and phage genomes, and report scaling laws on DNA to complement observations in language and vision. Evo generalizes across DNA, RNA, and proteins, enabling zero-shot function prediction competitive with domain-specific language models and the generation of functional CRISPR-Cas and transposon systems, representing the first examples of protein-RNA and protein-DNA codesign with a language model. Evo also learns how small mutations affect whole-organism fitness and generates megabase-scale sequences with plausible genomic architecture. These prediction and generation capabilities span molecular to genomic scales of complexity, advancing our understanding and control of biology.

Complete genomes of Asgard archaea reveal diverse integrated and mobile genetic elements

Asgard archaea are of great interest as the progenitors of Eukaryotes, but little is known about the mobile genetic elements (MGEs) that may shape their ongoing evolution. Here, we describe MGEs that replicate in Atabeyarchaeia, a wetland Asgard archaea lineage represented by two complete genomes. We used soil depth-resolved population metagenomic data sets to track 18 MGEs for which genome structures were defined and precise chromosome integration sites could be identified for confident host linkage. Additionally, we identified a complete 20.67 kbp circular plasmid and two family-level groups of viruses linked to Atabeyarchaeia, via CRISPR spacer targeting. Closely related 40 kbp viruses possess a hypervariable genomic region encoding combinations of specific genes for small cysteine-rich proteins structurally similar to restriction-homing endonucleases. One 10.9 kbp integrative conjugative element (ICE) integrates genomically into the Atabeyarchaeum deiterrae-1 chromosome and has a 2.5 kbp circularizable element integrated within it. The 10.9 kbp ICE encodes an expressed Type IIG restriction-modification system with a sequence specificity matching an active methylation motif identified by Pacific Biosciences (PacBio) high-accuracy long-read (HiFi) metagenomic sequencing. Restriction-modification of Atabeyarchaeia differs from that of another coexisting Asgard archaea, Freyarchaeia, which has few identified MGEs but possesses diverse defense mechanisms, including DISARM and Hachiman, not found in Atabeyarchaeia. Overall, defense systems and methylation mechanisms of Asgard archaea likely modulate their interactions with MGEs, and integration/excision and copy number variation of MGEs in turn enable host genetic versatility.

Crosstalk between three CRISPR-Cas types enables primed type VI-A adaptation in Listeria seeligeri

CRISPR-Cas systems confer adaptive immunity to their prokaryotic hosts through the process of adaptation, where sequences are captured from foreign nucleic acids and integrated as spacers in the CRISPR array, and thereby enable crRNA-guided interference against new threats. While the Cas1-2 integrase is critical for adaptation, it is absent from many CRISPR-Cas loci, rendering the mechanism of spacer acquisition unclear for these systems. Here we show that the RNA-targeting type VI-A CRISPR system of Listeria seeligeri acquires spacers from DNA substrates through the action of a promiscuous Cas1-2 integrase encoded by a co-occurring type II-C system, in a transcription-independent manner. We further demonstrate that the type II-C integration complex is strongly stimulated by preexisting spacers in a third CRISPR system (type I-B) which imperfectly match phage targets and prime type VI-A adaptation. Altogether, our results reveal an unprecedented degree of communication among CRISPR-Cas loci encoded by a single organism.

Metagenomic insights into microalgae-bacterium-virus interactions and viral functions in phycosphere facing environmental fluctuations

Despite the ecological and biotechnological significance of microalgae-bacterium symbionts, the response of host-virus interactions to external environmental fluctuations and the role of viruses in phycosphere remain largely unexplored. Herein, we employed algal-bacterial granular sludge (ABGS) with varying light intensity and organic carbon loading to investigate the mechanisms of microalgae-bacterium-virus symbionts in response to environmental fluctuations. Metagenomics revealed that enhanced light intensity decreased the diversity of microalgae, so did the diversity of symbiotic bacteria and viruses. As carbon sources decreased, bacteria prompted horizontal gene transfer in phycosphere by 12.76 %-157.40 %, increased the proportion of oligotrophs as keystone species (0.00 % vs 14.29 %) as well as viruses using oligotrophs as hosts (18.52 % vs 25.00 %). Furthermore, virus-carried auxiliary metabolic genes (AMGs) and biosynthetic gene clusters (BGCs) encoding vitamin B12 synthesis (e.g., cobS), antioxidation (e.g., queC), and microbial aggregation (e.g., cysE). Additionally, phylogenetic and similarity analysis further revealed the evolutionary origin and potential horizontal transfer of the AMGs and BGCs, which could potentially enhance the adaptability of bacteria and eukaryotic microalgae. Overall, our research demonstrates that environmental fluctuations have cascading effects on the microalgae-bacteria-virus interactions, and emphasizes the important role of viruses in maintaining the stability of the phycosphere symbiotic community.

Differentiation of the Anammox core microbiome: Unraveling the evolutionary impetus of scalable gene flow

Anaerobic ammonium oxidation bacteria (AAOB), distinguished by their unique autotrophic nitrogen metabolism, hold pivotal positions in the global nitrogen cycle and environmental biotechnologies. However, the ecophysiology and evolution of AAOB remain poorly understood, attributed to the absence of monocultures. Hence, a comprehensive elucidation of the AAOB-dominated core microbiome, anammox core, is imperative to further completing the theory of engineered nitrogen removal and ecological roles of anammox. Performing taxonomic and phylogenetic analyses on collected genome repertoires, we show here that Candidatus Brocadia and Candidatus Kuenenia possesses a more compact core than Candidatus Jettenia, which partly explains why the latter has a less common ecological presence. Evidence of gene flow is particularly striking in functions related to biosynthesis and oxygen detoxification, underscoring the evolutionary forces driving lineage and core differentiation. Furthermore, CRISPR spacer traceback of the AAOB metagenome-assembled genomes (MAGs) reveals a series of genetic traces for the concealed phages. By reconceptualizing the functional divergence of AAOB with the historical role of phages, we ultimately propose a coevolutionary framework to understand the evolutionary trajectory of anammox microecology. The discoveries provided in this study offer new insights into understanding the evolution of AAOB and the ecology of anammox.

Targeted phage hunting to specific Klebsiella pneumoniae clinical isolates is an efficient antibiotic resistance and infection control strategy

Klebsiella pneumoniae is one of the most threatening multi-drug-resistant pathogens today, with phage therapy being a promising alternative for personalized treatments. However, the intrinsic capsule diversity in Klebsiella spp. poses a substantial barrier to the phage host range, complicating the development of broad-spectrum phage-based treatments. Here, we have isolated and genomically characterized phages capable of infecting each of the acquired 77 reference serotypes of Klebsiella spp., including capsular types widespread among high-risk K. pneumoniae clones causing nosocomial infections. We demonstrated the possibility of isolating phages for all capsular types in the collection, revealing high capsular specificity among taxonomically related phages, in contrast to a few phages that exhibited broad-spectrum infection capabilities. To decipher the determinants of the specificity of these phages, we focused on their receptor-binding proteins, with particular attention to depolymerases. We also explored the possibility of designing a broad-spectrum phage cocktail based on phages isolated in reference capsular-type strains and determining the ability to lyse relevant clinical isolates. A combination of 12 phages capable of infecting 55% of the reference Klebsiella spp. serotypes was tested on a panel of carbapenem-resistant K. pneumoniae clinical isolates. Thirty-one percent of isolates were susceptible to the phage cocktail. However, our results suggest that in a highly variable encapsulated bacterial host, phage hunting must be directed to the specific Klebsiella isolates. This work is a step forward in the understanding of the complexity of phage-host interactions and highlights the importance of implementing precise and phage-specific strategies to treat K. pneumoniae infections worldwide.IMPORTANCEThe emergence of resistant bacteria is a serious global health problem. In the absence of effective treatments, phages are a personalized and effective therapeutic alternative. However, little is still known about phage-host interactions, which are key to implementing effective strategies. Here, we focus on the study of Klebsiella pneumoniae, a highly pathogenic encapsulated bacterium. The complexity and variability of the capsule, where in most cases phage receptors are found, make it difficult for phage-based treatments. Here, we isolated a large collection of Klebsiella phages against all the reference strains and in a cohort of clinical isolates. Our results suggest that clinical isolates represent a challenge, especially high-risk clones. Thus, we propose targeted phage hunting as an effective strategy to implement phage-derived therapies. Our results are a step forward for new phage-based strategies to control K. pneumoniae infections, highlighting the importance of understanding phage-host interactions to design personalized treatments against Klebsiella spp.

Diverse viral cas genes antagonize CRISPR immunity

Prokaryotic CRISPR-Cas immunity is subverted by anti-CRISPRs (Acrs), which inhibit Cas protein activities when expressed during the phage lytic cycle or from resident prophages or plasmids1. Acrs often bind to specific cognate Cas proteins, and hence inhibition is typically limited to a single CRISPR-Cas subtype2. Furthermore, although acr genes are frequently organized together in phage-associated gene clusters3, how such inhibitors initially evolve has remained unclear. Here we investigated the Acr content and inhibition specificity of diverse Listeria isolates, which naturally harbour four CRISPR-Cas systems (types I-B, II-A, II-C and VI-A). We observed widespread antagonism of CRISPR, which we traced to 11 previously unknown and 4 known acr gene families encoded by endogenous mobile elements. Among these were two Acrs that possess sequence homology to type I-B Cas proteins, one of which assembles into a defective interference complex. Surprisingly, an additional type I-B Cas homologue did not affect type I immunity, but instead inhibited the RNA-targeting type VI CRISPR system by means of CRISPR RNA (crRNA) degradation. By probing viral sequence databases, we detected abundant orphan cas genes located within putative anti-defence gene clusters. Among them, we verified the activity of a particularly broad-spectrum cas3 homologue that inhibits type I-B, II-A and VI-A CRISPR immunity. Our observations provide direct evidence of Acr evolution by cas gene co-option, and new genes with potential for broad-spectrum control of genome editing technologies.

Methanotrophic Methanoperedens archaea host diverse and interacting extrachromosomal elements

Methane emissions are mitigated by anaerobic methane-oxidizing archaea, including Methanoperedens. Some Methanoperedens host huge extrachromosomal genetic elements (ECEs) called Borgs that may modulate their activity, yet the broader diversity of Methanoperedens ECEs is understudied. Here we report small enigmatic linear ECEs, circular viruses and unclassified ECEs that are predicted to replicate within Methanoperedens. Linear ECEs have inverted terminal repeats, tandem repeats and coding patterns that are strongly reminiscent of Borgs, but they are only 52-145 kb in length. As they share proteins with Borgs and Methanoperedens, we refer to them as mini-Borgs. Mini-Borgs are genetically diverse and can be assigned to at least five family-level groups. We identify eight families of Methanoperedens viruses, some of which encode multi-haem cytochromes, and circular ECEs encoding transposon-associated TnpB genes with proximal population-heterogeneous CRISPR arrays. These ECEs exchange genetic information with each other and with Methanoperedens, probably impacting their archaeal host activity and evolution.

Global marine microbial diversity and its potential in bioprospecting

The past two decades has witnessed a remarkable increase in the number of microbial genomes retrieved from marine systems1,2. However, it has remained challenging to translate this marine genomic diversity into biotechnological and biomedical applications3,4. Here we recovered 43,191 bacterial and archaeal genomes from publicly available marine metagenomes, encompassing a wide range of diversity with 138 distinct phyla, redefining the upper limit of marine bacterial genome size and revealing complex trade-offs between the occurrence of CRISPR-Cas systems and antibiotic resistance genes. In silico bioprospecting of these marine genomes led to the discovery of a novel CRISPR-Cas9 system, ten antimicrobial peptides, and three enzymes that degrade polyethylene terephthalate. In vitro experiments confirmed their effectiveness and efficacy. This work provides evidence that global-scale sequencing initiatives advance our understanding of how microbial diversity has evolved in the oceans and is maintained, and demonstrates how such initiatives can be sustainably exploited to advance biotechnology and biomedicine.

Metagenome-assembled microbial genomes from Parkinson's disease fecal samples

The human gut microbiome composition has been linked to Parkinson's disease (PD). However, knowledge of the gut microbiota on the genome level is still limited. Here we performed deep metagenomic sequencing and binning to build metagenome-assembled genomes (MAGs) from 136 human fecal microbiomes (68 PD samples and 68 control samples). We constructed 952 non-redundant high-quality MAGs and compared them between PD and control groups. Among these MAGs, there were 22 different genomes of Collinsella and Prevotella, indicating high variability of those genera in the human gut environment. Microdiversity analysis indicated that Ruminococcus bromii was statistically significantly (p < 0.002) more diverse on the strain level in the control samples compared to the PD samples. In addition, by clustering all genes and performing presence-absence analysis between groups, we identified several control-specific (p < 0.05) related genes, such as speF and Fe-S oxidoreductase. We also report detailed annotation of MAGs, including Clusters of Orthologous Genes (COG), Cas operon type, antiviral gene, prophage, and secondary metabolites biosynthetic gene clusters, which can be useful for providing a reference for future studies.

Unveiling the microbial realm with VEBA 2.0: a modular bioinformatics suite for end-to-end genome-resolved prokaryotic, (micro)eukaryotic and viral multi-omics from either short- or long-read sequencing

The microbiome is a complex community of microorganisms, encompassing prokaryotic (bacterial and archaeal), eukaryotic, and viral entities. This microbial ensemble plays a pivotal role in influencing the health and productivity of diverse ecosystems while shaping the web of life. However, many software suites developed to study microbiomes analyze only the prokaryotic community and provide limited to no support for viruses and microeukaryotes. Previously, we introduced the Viral Eukaryotic Bacterial Archaeal (VEBA) open-source software suite to address this critical gap in microbiome research by extending genome-resolved analysis beyond prokaryotes to encompass the understudied realms of eukaryotes and viruses. Here we present VEBA 2.0 with key updates including a comprehensive clustered microeukaryotic protein database, rapid genome/protein-level clustering, bioprospecting, non-coding/organelle gene modeling, genome-resolved taxonomic/pathway profiling, long-read support, and containerization. We demonstrate VEBA's versatile application through the analysis of diverse case studies including marine water, Siberian permafrost, and white-tailed deer lung tissues with the latter showcasing how to identify integrated viruses. VEBA represents a crucial advancement in microbiome research, offering a powerful and accessible software suite that bridges the gap between genomics and biotechnological solutions.

Pathogen dynamics and discovery of novel viruses and enzymes by deep nucleic acid sequencing of wastewater

Wastewater contains an extensive reservoir of genetic information, yet largely unexplored. Here, we analyzed by high-throughput sequencing total nucleic acids extracted from wastewater samples collected during a 17 month-period in Berlin, Germany. By integrating global wastewater datasets and applying a novel computational approach to accurately identify viral strains within sewage RNA-sequencing data, we demonstrated the emergence and global dissemination of a specific astrovirus strain. Astrovirus abundance and sequence variation mirrored temporal and spatial patterns of infection, potentially serving as footprints of specific timeframes and geographical locations. Additionally, we revealed more than 100,000 sequence contigs likely originating from novel viral species, exhibiting distinct profiles in total RNA and DNA datasets and including undescribed bunyaviruses and parvoviruses. Finally, we identified thousands of new CRISPR-associated protein sequences, including Transposase B (TnpB), a class of compact, RNA-guided DNA editing enzymes. Collectively, our findings underscore the potential of high-throughput sequencing of total nucleic acids derived from wastewater for a broad range of applications.

Characterization of Ligilactobacillus salivarius CRISPR-Cas systems

Ligilactobacillus is a diverse genus among lactobacilli with phenotypes that reflect adaptation to various hosts. CRISPR-Cas systems are highly prevalent within lactobacilli, and Ligilactobacillus salivarius, the most abundant species of Ligilactobacillus, possesses both DNA- and RNA-targeting CRISPR-Cas systems. In this study, we explore the presence and functional properties of I-B, I-C, I-E, II-A, and III-A CRISPR-Cas systems in over 500 Ligilactobacillus genomes, emphasizing systems found in L. salivarius. We examined the I-E, II-A, and III-A CRISPR-Cas systems of two L. salivarius strains and observed occurrences of split cas genes and differences in CRISPR RNA maturation in native hosts. This prompted testing of the single Cas9 and multiprotein Cascade and Csm CRISPR-Cas effector complexes in a cell-free context to demonstrate the functionality of these systems. We also predicted self-targeting spacers within L. salivarius CRISPR-Cas systems and found that nearly a third of L. salivarius genomes possess unique self-targeting spacers that generally target elements other than prophages. With these two L. salivarius strains, we performed prophage induction coupled with RNA sequencing and discovered that the prophages residing within these strains are inducible and likely active elements, despite targeting by CRISPR-Cas systems. These findings deepen our comprehension of CRISPR-Cas systems in L. salivarius, further elucidating their relationship with associated prophages and providing a functional basis for the repurposing of these Cas effectors for bacterial manipulation.

IMPORTANCE

Ligilactobacillus salivarius is a diverse bacterial species widely used in the food and dietary supplement industries. In this study, we investigate the occurrence and diversity of their adaptive immune systems, CRISPR-Cas, in over 500 genomes. We establish their function and provide insights into their role in the interplay between the bacterial host and the predatory phages that infect them. Such findings expand our knowledge about these important CRISPR-Cas immune systems widespread across the bacterial tree of life and also provide a technical basis for the repurposing of these molecular machines for the development of molecular biology tools and the manipulation and engineering of bacteria and other life forms.

Viral and Bacterial Community Dynamics in Food Waste and Digestate from Full-Scale Biogas Plants

Anaerobic digestion (AD) is commonly used in food waste treatment. Prokaryotic microbial communities in AD of food waste have been comprehensively studied. The role of viruses, known to affect microbial dynamics and metabolism, remains largely unexplored. This study employed metagenomic analysis and recovered 967 high-quality viral bins within food waste and digestate derived from 8 full-scale biogas plants. The diversity of viral communities was higher in digestate. In silico predictions linked 20.8% of viruses to microbial host populations, highlighting possible virus predators of key functional microbes. Lineage-specific virus-host ratio varied, indicating that viral infection dynamics might differentially affect microbial responses to the varying process parameters. Evidence for virus-mediated gene transfer was identified, emphasizing the potential role of viruses in controlling the microbiome. AD altered the specific process parameters, potentially promoting a shift in viral lifestyle from lysogenic to lytic. Viruses encoding auxiliary metabolic genes (AMGs) were involved in microbial carbon and nutrient cycling, and most AMGs were transcriptionally expressed in digestate, meaning that viruses with active functional states were likely actively involved in AD. These findings provided a comprehensive profile of viral and bacterial communities and expanded knowledge of the interactions between viruses and hosts in food waste and digestate.

Bioinformatic analysis of type III CRISPR systems reveals key properties and new effector families

Recognition of RNA from invading mobile genetic elements (MGE) prompts type III CRISPR systems to activate an HD nuclease domain and/or a nucleotide cyclase domain in the Cas10 subunit, eliciting an immune response. The cyclase domain can generate a range of nucleotide second messengers, which in turn activate a diverse family of ancillary effector proteins. These provide immunity by non-specific degradation of host and MGE nucleic acids or proteins, perturbation of membrane potentials, transcriptional responses, or the arrest of translation. The wide range of nucleotide activators and downstream effectors generates a complex picture that is gradually being resolved. Here, we carry out a global bioinformatic analysis of type III CRISPR loci in prokaryotic genomes, defining the relationships of Cas10 proteins and their ancillary effectors. Our study reveals that cyclic tetra-adenylate is by far the most common signalling molecule used and that many loci have multiple effectors. These typically share the same activator and may work synergistically to combat MGE. We propose four new candidate effector protein families and confirm experimentally that the Csm6-2 protein, a highly diverged, fused Csm6 effector, is a ribonuclease activated by cyclic hexa-adenylate.

An ecological-evolutionary perspective on the genomic diversity and habitat preferences of the Acidobacteriota

Members of the phylum Acidobacteriota inhabit a wide range of ecosystems including soils. We analyzed the global patterns of distribution and habitat preferences of various Acidobacteriota lineages across major ecosystems (soil, engineered, host-associated, marine, non-marine saline and alkaline, and terrestrial non-soil ecosystem) in 248,559 publicly available metagenomic datasets. Classes Terriglobia, Vicinamibacteria, Blastocatellia, and Thermoanaerobaculia were highly ubiquitous and showed clear preference to soil over non-soil habitats, class Polarisedimenticolia showed comparable ubiquity and preference between soil and non-soil habitats, while classes Aminicenantia and Holophagae showed preferences to non-soil habitats. However, while specific preferences were observed, most Acidobacteriota lineages were habitat generalists rather than specialists, with genomic and/or metagenomic fragments recovered from soil and non-soil habitats at various levels of taxonomic resolution. Comparative analysis of 1930 genomes strongly indicates that phylogenetic affiliation plays a more important role than the habitat from which the genome was recovered in shaping the genomic characteristics and metabolic capacities of the Acidobacteriota. The observed lack of strong habitat specialization and habitat transition driven lineage evolution in the Acidobacteriota suggest ready cross colonization between soil and non-soil habitats. We posit that such capacity is key to the successful establishment of Acidobacteriota as a major component in soil microbiomes post ecosystem disturbance events or during pedogenesis.

RNA-guided RNA silencing by an Asgard archaeal Argonaute

Argonaute proteins are the central effectors of RNA-guided RNA silencing pathways in eukaryotes, playing crucial roles in gene repression and defense against viruses and transposons. Eukaryotic Argonautes are subdivided into two clades: AGOs generally facilitate miRNA- or siRNA-mediated silencing, while PIWIs generally facilitate piRNA-mediated silencing. It is currently unclear when and how Argonaute-based RNA silencing mechanisms arose and diverged during the emergence and early evolution of eukaryotes. Here, we show that in Asgard archaea, the closest prokaryotic relatives of eukaryotes, an evolutionary expansion of Argonaute proteins took place. In particular, a deep-branching PIWI protein (HrAgo1) encoded by the genome of the Lokiarchaeon 'Candidatus Harpocratesius repetitus' shares a common origin with eukaryotic PIWI proteins. Contrasting known prokaryotic Argonautes that use single-stranded DNA as guides and/or targets, HrAgo1 mediates RNA-guided RNA cleavage, and facilitates gene silencing when expressed in human cells and supplied with miRNA precursors. A cryo-EM structure of HrAgo1, combined with quantitative single-molecule experiments, reveals that the protein displays structural features and target-binding modes that are a mix of those of eukaryotic AGO and PIWI proteins. Thus, this deep-branching archaeal PIWI may have retained an ancestral molecular architecture that preceded the functional and mechanistic divergence of eukaryotic AGOs and PIWIs.

Characteristics and immune functions of the endogenous CRISPR-Cas systems in myxobacteria

The clustered regularly interspaced short palindromic repeats and their associated proteins (CRISPR-Cas) system widely occurs in prokaryotic organisms to recognize and destruct genetic invaders. Systematic collation and characterization of endogenous CRISPR-Cas systems are conducive to our understanding and potential utilization of this natural genetic machinery. In this study, we screened 39 complete and 692 incomplete genomes of myxobacteria using a combined strategy to dispose of the abridged genome information and revealed at least 19 CRISPR-Cas subtypes, which were distributed with a taxonomic difference and often lost stochastically in intraspecies strains. The cas genes in each subtype were evolutionarily clustered but deeply separated, while most of the CRISPRs were divided into four types based on the motif characteristics of repeat sequences. The spacers recorded in myxobacterial CRISPRs were in high G+C content, matching lots of phages, tiny amounts of plasmids, and, surprisingly, massive organismic genomes. We experimentally demonstrated the immune and self-target immune activities of three endogenous systems in Myxococcus xanthus DK1622 against artificial genetic invaders and revealed the microhomology-mediated end-joining mechanism for the immunity-induced DNA repair but not homology-directed repair. The panoramic view and immune activities imply potential omnipotent immune functions and applications of the endogenous CRISPR-Cas machinery.

IMPORTANCE

Serving as an adaptive immune system, clustered regularly interspaced short palindromic repeats and their associated proteins (CRISPR-Cas) empower prokaryotes to fend off the intrusion of external genetic materials. Myxobacteria are a collective of swarming Gram-stain-negative predatory bacteria distinguished by intricate multicellular social behavior. An in-depth analysis of their intrinsic CRISPR-Cas systems is beneficial for our understanding of the survival strategies employed by host cells within their environmental niches. Moreover, the experimental findings presented in this study not only suggest the robust immune functions of CRISPR-Cas in myxobacteria but also their potential applications.

Type IV-A3 CRISPR-Cas systems drive inter-plasmid conflicts by acquiring spacers in trans

Plasmid-encoded type IV-A CRISPR-Cas systems lack an acquisition module, feature a DinG helicase instead of a nuclease, and form ribonucleoprotein complexes of unknown biological functions. Type IV-A3 systems are carried by conjugative plasmids that often harbor antibiotic-resistance genes and their CRISPR array contents suggest a role in mediating inter-plasmid conflicts, but this function remains unexplored. Here, we demonstrate that a plasmid-encoded type IV-A3 system co-opts the type I-E adaptation machinery from its host, Klebsiella pneumoniae (K. pneumoniae), to update its CRISPR array. Furthermore, we reveal that robust interference of conjugative plasmids and phages is elicited through CRISPR RNA-dependent transcriptional repression. By silencing plasmid core functions, type IV-A3 impacts the horizontal transfer and stability of targeted plasmids, supporting its role in plasmid competition. Our findings shed light on the mechanisms and ecological function of type IV-A3 systems and demonstrate their practical efficacy for countering antibiotic resistance in clinically relevant strains.

A panoramic view of the virosphere in three wastewater treatment plants by integrating viral-like particle-concentrated and traditional non-concentrated metagenomic approaches

Wastewater biotreatment systems harbor a rich diversity of microorganisms, and the effectiveness of biotreatment systems largely depends on the activity of these microorganisms. Specifically, viruses play a crucial role in altering microbial behavior and metabolic processes throughout their infection phases, an aspect that has recently attracted considerable interest. Two metagenomic approaches, viral-like particle-concentrated (VPC, representing free viral-like particles) and non-concentrated (NC, representing the cellular fraction), were employed to assess their efficacy in revealing virome characteristics, including taxonomy, diversity, host interactions, lifestyle, dynamics, and functional genes across processing units of three wastewater treatment plants (WWTPs). Our findings indicate that each approach offers unique insights into the viral community and functional composition. Their combined use proved effective in elucidating WWTP viromes. We identified nearly 50,000 viral contigs, with Cressdnaviricota and Uroviricota being the predominant phyla in the VPC and NC fractions, respectively. Notably, two pathogenic viral families, Asfarviridae and Adenoviridae, were commonly found in these WWTPs. We also observed significant differences in the viromes of WWTPs processing different types of wastewater. Additionally, various phage-derived auxiliary metabolic genes (AMGs) were active at the RNA level, contributing to the metabolism of the microbial community, particularly in carbon, sulfur, and phosphorus cycling. Moreover, we identified 29 virus-carried antibiotic resistance genes (ARGs) with potential for host transfer, highlighting the role of viruses in spreading ARGs in the environment. Overall, this study provides a detailed and integrated view of the virosphere in three WWTPs through the application of VPC and NC metagenomic approaches. Our findings enhance the understanding of viral communities, offering valuable insights for optimizing the operation and regulation of wastewater treatment systems.

Discarded diversity: Novel megaphages, auxiliary metabolic genes, and virally encoded CRISPR-Cas systems in landfills

Background

Viruses are the most abundant microbial entity on the planet, impacting microbial community structure and ecosystem services. Despite outnumbering Bacteria and Archaea by an order of magnitude, viruses have been comparatively underrepresented in reference databases. Metagenomic examinations have illustrated that viruses of Bacteria and Archaea have been specifically understudied in engineered environments. Here we employed metagenomic and computational biology methods to examine the diversity, host interactions, and genetic systems of viruses predicted from 27 samples taken from three municipal landfills across North America.

Results

We identified numerous viruses that are not represented in reference databases, including the third largest bacteriophage genome identified to date (~678 kbp), and note a cosmopolitan diversity of viruses in landfills that are distinct from viromes in other systems. Host-virus interactions were examined via host CRISPR spacer to viral protospacer mapping which captured hyper-targeted viral populations and six viral populations predicted to infect across multiple phyla. Virally-encoded auxiliary metabolic genes (AMGs) were identified with the potential to augment hosts' methane, sulfur, and contaminant degradation metabolisms, including AMGs not previously reported in literature. CRISPR arrays and CRISPR-Cas systems were identified from predicted viral genomes, including the two largest bacteriophage genomes to contain these genetic features. Some virally encoded Cas effector proteins appear distinct relative to previously reported Cas systems and are interesting targets for potential genome editing tools.

Conclusions

Our observations indicate landfills, as heterogeneous contaminated sites with unique selective pressures, are key locations for diverse viruses and atypical virus-host dynamics.

Exploring the Frozen Armory: Antiphage Defense Systems in Cold-Adapted Bacteria with a Focus on CRISPR-Cas Systems

Our understanding of the antiphage defense system arsenal in bacteria is rapidly expanding, but little is known about its occurrence in cold-adapted bacteria. In this study, we aim to shed light on the prevalence and distribution of antiphage defense systems in cold-adapted bacteria, with a focus on CRISPR-Cas systems. Using bioinformatics tools, Prokaryotic Antiviral Defense LOCator (PADLOC) and CRISPRCasTyper, we mapped the presence and diversity of antiphage defense systems in 938 available genomes of cold-adapted bacteria from diverse habitats. We confirmed that CRISPR-Cas systems are less frequent in cold-adapted bacteria, compared to mesophilic and thermophilic species. In contrast, several antiphage defense systems, such as dXTPases and DRTs, appear to be more frequently compared to temperate bacteria. Additionally, our study provides Cas endonuclease candidates with a potential for further development into cold-active CRISPR-Cas genome editing tools. These candidates could have broad applications in research on cold-adapted organisms. Our study provides a first-time map of antiphage defense systems in cold-adapted bacteria and a detailed overview of CRISPR-Cas diversity.

Specificities and commonalities of the Planctomycetes plasmidome

Plasmids, despite their critical role in antibiotic resistance and modern biotechnology, are understood in only a few bacterial groups in terms of their natural ecological dynamics. The bacterial phylum Planctomycetes, known for its unique molecular and cellular biology, has a largely unexplored plasmidome. This study offers a thorough exploration of the diversity of natural plasmids within Planctomycetes, which could serve as a foundation for developing various genetic research tools for this phylum. Planctomycetes plasmids encode a broad range of biological functions and appear to have coevolved significantly with their host chromosomes, sharing many homologues. Recent transfer events of insertion sequences between cohabiting chromosomes and plasmids were also observed. Interestingly, 64% of plasmid genes are distantly related to either chromosomally encoded genes or have homologues in plasmids from other bacterial groups. The planctomycetal plasmidome is composed of 36% exclusive proteins. Most planctomycetal plasmids encode a replication initiation protein from the Replication Protein A family near a putative iteron-containing replication origin, as well as active type I partition systems. The identification of one conjugative and three mobilizable plasmids suggests the occurrence of horizontal gene transfer via conjugation within this phylum. This comprehensive description enhances our understanding of the plasmidome of Planctomycetes and its potential implications in antibiotic resistance and biotechnology.

CoCas9 is a compact nuclease from the human microbiome for efficient and precise genome editing

The expansion of the CRISPR-Cas toolbox is highly needed to accelerate the development of therapies for genetic diseases. Here, through the interrogation of a massively expanded repository of metagenome-assembled genomes, mostly from human microbiomes, we uncover a large variety (n = 17,173) of type II CRISPR-Cas loci. Among these we identify CoCas9, a strongly active and high-fidelity nuclease with reduced molecular size (1004 amino acids) isolated from an uncultivated Collinsella species. CoCas9 is efficiently co-delivered with its sgRNA through adeno associated viral (AAV) vectors, obtaining efficient in vivo editing in the mouse retina. With this study we uncover a collection of previously uncharacterized Cas9 nucleases, including CoCas9, which enriches the genome editing toolbox.

Diverse and abundant phages exploit conjugative plasmids

Phages exert profound evolutionary pressure on bacteria by interacting with receptors on the cell surface to initiate infection. While the majority of phages use chromosomally encoded cell surface structures as receptors, plasmid-dependent phages exploit plasmid-encoded conjugation proteins, making their host range dependent on horizontal transfer of the plasmid. Despite their unique biology and biotechnological significance, only a small number of plasmid-dependent phages have been characterized. Here we systematically search for new plasmid-dependent phages targeting IncP and IncF plasmids using a targeted discovery platform, and find that they are common and abundant in wastewater, and largely unexplored in terms of their genetic diversity. Plasmid-dependent phages are enriched in non-canonical types of phages, and all but one of the 65 phages we isolated were non-tailed, and members of the lipid-containing tectiviruses, ssDNA filamentous phages or ssRNA phages. We show that plasmid-dependent tectiviruses exhibit profound differences in their host range which is associated with variation in the phage holin protein. Despite their relatively high abundance in wastewater, plasmid-dependent tectiviruses are missed by metaviromic analyses, underscoring the continued importance of culture-based phage discovery. Finally, we identify a tailed phage dependent on the IncF plasmid, and find related structural genes in phages that use the orthogonal type 4 pilus as a receptor, highlighting the evolutionarily promiscuous use of these distinct contractile structures by multiple groups of phages. Taken together, these results indicate plasmid-dependent phages play an under-appreciated evolutionary role in constraining horizontal gene transfer via conjugative plasmids.

Diverse Class 2 CRISPR Effectors as Active Nucleases with Expanded Targeting Capabilities

CRISPR-Cas systems have proven effective in a variety of applications due to their ease of use and relatively high editing efficiency. Yet, any individual CRISPR-Cas system has inherent limitations, necessitating a diversity of RNA-guided nucleases to suit applications with distinct needs. We searched through metagenomic sequences to identify RNA-guided nucleases and found enzymes from diverse CRISPR-Cas types and subtypes, the most promising of which we developed into gene-editing platforms. Based on prior annotations of the metagenomic sequences, we establish the likely taxa and sampling locations where Class 2 CRISPR-Cas systems active in eukaryotes may be found. The newly discovered systems show robust capabilities as gene editors and base editors.

Discovery and engineering of AiEvo2, a novel Cas12a nuclease for human gene editing applications

The precision of gene editing technology is critical to creating safe and effective therapies for treating human disease. While the programmability of CRISPR-Cas systems has allowed for rapid innovation of new gene editing techniques, the off-target activity of these enzymes has hampered clinical development for novel therapeutics. Here, we report the identification and characterization of a novel CRISPR-Cas12a enzyme from Acinetobacter indicus (AiCas12a). We engineer the nuclease (termed AiEvo2) for increased specificity, protospacer adjacent motif recognition, and efficacy on a variety of human clinical targets. AiEvo2 is highly precise and able to efficiently discriminate between normal and disease-causing alleles in Huntington's patient-derived cells by taking advantage of a single nucleotide polymorphism on the disease-associated allele. AiEvo2 efficiently edits several liver-associated target genes including PCSK9 and TTR when delivered to primary hepatocytes as mRNA encapsulated in a lipid nanoparticle. The enzyme also engineers an effective CD19 chimeric antigen receptor-T-cell therapy from primary human T cells using multiplexed simultaneous editing and chimeric antigen receptor insertion. To further ensure precise editing, we engineered an anti-CRISPR protein to selectively inhibit off-target gene editing while retaining therapeutic on-target editing. The engineered AiEvo2 nuclease coupled with a novel engineered anti-CRISPR protein represents a new way to control the fidelity of editing and improve the safety and efficacy of gene editing therapies.

Pangenome analysis of Shewanella xiamenensis revealed important genetic traits concerning genetic diversity, pathogenicity and antibiotic resistance

BACKGROUND

Shewanella xiamenensis, widely distributed in natural environments, has long been considered as opportunistic pathogen. Recently, significant changes in the resistance spectrum have been observed in S. xiamenensis, due to acquired antibiotic resistance genes. Therefore, a pan-genome analysis was conducted to illuminate the genomic changes in S. xiamenensis.

RESULTS

Phylogenetic analysis revealed three major clusters and three singletons, among which close relationship between several strains was discovered, regardless of their host and niches. The "open" genomes with diversity of accessory and strain-specific genomes took advantage towards diversity environments. The purifying selection pressure was the main force on genome evolution, especially in conservative genes. Only 53 gene families were under positive selection pressure. Phenotypic resistance analysis revealed 21 strains were classified as multi-drug resistance (MDR). Ten types of antibiotic resistance genes and two heavy metal resistance operons were discovered in S. xiamenensis. Mobile genetic elements and horizontal gene transfer increased genome diversity and were closely related to MDR strains. S. xiamenensis carried a variety of virulence genes and macromolecular secretion systems, indicating their important roles in pathogenicity and adaptability. Type IV secretion system was discovered in 15 genomes with various sequence structures, indicating it was originated from different donors through horizontal gene transfer.

CONCLUSIONS

This study provided with a detailed insight into the changes in the pan-genome of S. xiamenensis, highlighting its capability to acquire new mobile genetic elements and resistance genes for its adaptation to environment and pathogenicity to human and animals.

Increased mutations in lipopolysaccharide biosynthetic genes cause time-dependent development of phage resistance in Salmonella

Understanding how bacteria evolve resistance to phages has implications for phage-based therapies and microbial evolution. In this study, the susceptibility of 335 Salmonella isolates to the wide host range Salmonella phage BPSELC-1 was tested. Potentially significant gene sets that could confer resistance were identified using bioinformatics approaches based on phage susceptibility phenotypes; more than 90 potential antiphage defense gene sets, including those involved in lipopolysaccharide (LPS) biosynthesis, DNA replication, secretion systems, and respiratory chain, were found. The evolutionary dynamics of Salmonella resistance to phage were assessed through laboratory evolution experiments, which showed that phage-resistant mutants rapidly developed and exhibited genetic heterogeneity. Most representative Salmonella hosts (58.1% of 62) rapidly developed phage resistance within 24 h. All phage-resistant mutant clones exhibited genetic heterogeneity and observed mutations in LPS-related genes (rfaJ and rfaK) as well as other genes such as cellular respiration, transport, and cell replication-related genes. The study also identified potential trade-offs, indicating that bacteria tend to escape fitness trade-offs through multi-site mutations, all tested mutants increased sensitivity to polymyxin B, but this does not always affect their relative fitness or biofilm-forming capacity. Furthermore, complementing the rfaJ mutant gene could partially restore the phage sensitivity of phage-resistant mutants. These results provide insight into the phage resistance mechanisms of Salmonella and the complexity of bacterial evolution resulting from phage predation, which can inform future strategies for phage-based therapies and microbial evolution.

Comparative evaluation of bioinformatic tools for virus-host prediction and their application to a highly diverse community in the Cuatro Ciénegas Basin, Mexico

Due to the enormous diversity of non-culturable viruses, new viruses must be characterized using culture-independent techniques. The associated host is an important phenotypic feature that can be inferred from metagenomic viral contigs thanks to the development of several bioinformatic tools. Here, we compare the performance of recently developed virus-host prediction tools on a dataset of 1,046 virus-host pairs and then apply the best-performing tools to a metagenomic dataset derived from a highly diverse transiently hypersaline site known as the Archaean Domes (AD) within the Cuatro Ciénegas Basin, Coahuila, Mexico. Among host-dependent methods, alignment-based approaches had a precision of 66.07% and a sensitivity of 24.76%, while alignment-free methods had an average precision of 75.7% and a sensitivity of 57.5%. RaFAH, a virus-dependent alignment-based tool, had the best overall performance (F1_score = 95.7%). However, when predicting the host of AD viruses, methods based on public reference databases (such as RaFAH) showed lower inter-method agreement than host-dependent methods run against custom databases constructed from prokaryotes inhabiting AD. Methods based on custom databases also showed the greatest agreement between the source environment and the predicted host taxonomy, habitat, lifestyle, or metabolism. This highlights the value of including custom data when predicting hosts on a highly diverse metagenomic dataset, and suggests that using a combination of methods and qualitative validations related to the source environment and predicted host biology can increase the number of correct predictions. Finally, these predictions suggest that AD viruses infect halophilic archaea as well as a variety of bacteria that may be halophilic, halotolerant, alkaliphilic, thermophilic, oligotrophic, sulfate-reducing, or marine, which is consistent with the specific environment and the known geological and biological evolution of the Cuatro Ciénegas Basin and its microorganisms.