A simple, fast, and accurate method of phylogenomic inference

Lightweight taxonomic profiling of long-read metagenomic datasets with Lemur and Magnet

The advent of long-read sequencing of microbiomes necessitates the development of new taxonomic profilers tailored to long-read shotgun metagenomic datasets. Here, we introduce Lemur and Magnet, a pair of tools optimized for lightweight and accurate taxonomic profiling for long-read shotgun metagenomic datasets. Lemur is a marker-gene-based method that leverages an EM algorithm to reduce false positive calls while preserving true positives; Magnet is a whole-genome read-mapping-based method that provides detailed presence and absence calls for bacterial genomes. We demonstrate that Lemur and Magnet can run in minutes to hours on a laptop with 32 GB of RAM, even for large inputs, a crucial feature given the portability of long-read sequencing machines. Furthermore, the marker gene database used by Lemur is only 4 GB and contains information from over 300,000 RefSeq genomes. Lemur and Magnet are open-source and available at https://github.com/treangenlab/lemur and https://github.com/treangenlab/magnet.

Comparative Genomics Revealing the Genomic Characteristics of Klebsiella variicola Clinical Isolates in China

Klebsiella variicola is an opportunistic pathogen often misidentified as Klebsiella pneumoniae, leading to misdiagnoses and inappropriate treatment in clinical settings. The genetic and molecular characteristics of clinically isolated K. variicola remain largely unexplored. We aim to fill this knowledge gap by examining the genomic properties of and evolutionary relationships between clinical isolates of K. variicola. The genomic data of 70 K. variicola strains were analyzed using whole-genome sequencing. A phylogenetic tree was generated based on the gene sequences from these K. variicola strains and public databases. Among the K. variicola strains, the drug resistance genes with the highest carrying rates were beta-lactamase and aminoglycoside. Locally isolated strains had a higher detection rate for virulence genes than those in public databases, with yersiniabactin genes being the most prevalent. The K locus types and MLST subtypes of the strains exhibited a dispersed distribution, with O3/O3a being the predominant subtype within the O category. In total, 28 isolates carried both IncFIB(K)_Kpn3 and IncFII_pKP91 replicons. This study underscores the importance of developing more effective diagnostic tools and therapeutic strategies for K. variicola infections. The continued surveillance and monitoring of K. variicola strains is essential for understanding the epidemiology of infections and informing public health strategies.

Step-by-Step Metagenomics for Food Microbiome Analysis: A Detailed Review

This review article offers a comprehensive overview of the current understanding of using metagenomic tools in food microbiome research. It covers the scientific foundation and practical application of genetic analysis techniques for microbial material from food, including bioinformatic analysis and data interpretation. The method discussed in the article for analyzing microorganisms in food without traditional culture methods is known as food metagenomics. This approach, along with other omics technologies such as nutrigenomics, proteomics, metabolomics, and transcriptomics, collectively forms the field of foodomics. Food metagenomics allows swift and thorough examination of bacteria and potential metabolic pathways by utilizing foodomic databases. Despite its established scientific basis and available bioinformatics resources, the research approach of food metagenomics outlined in the article is not yet widely implemented in industry. The authors believe that the integration of next-generation sequencing (NGS) with rapidly advancing digital technologies such as artificial intelligence (AI), the Internet of Things (IoT), and big data will facilitate the widespread adoption of this research strategy in microbial analysis for the food industry. This adoption is expected to enhance food safety and product quality in the near future.

Discovery of disease-adapted bacterial lineages in inflammatory bowel diseases

Gut bacteria are implicated in inflammatory bowel disease (IBD), but the strains driving these associations are unknown. Large-scale studies of microbiome evolution could reveal the imprint of disease on gut bacteria, thus pinpointing the strains and genes that may underlie inflammation. Here, we use stool metagenomes of thousands of IBD patients and healthy controls to reconstruct 140,000 strain genotypes, revealing hundreds of lineages enriched in IBD. We demonstrate that these strains are ancient, taxonomically diverse, and ubiquitous in humans. Moreover, disease-associated strains outcompete their healthy counterparts during inflammation, implying long-term adaptation to disease. Strain genetic differences map onto known axes of inflammation, including oxidative stress, nutrient biosynthesis, and immune evasion. Lastly, the loss of health-associated strains of Eggerthella lenta was predictive of fecal calprotectin, a biomarker of disease severity. Our work identifies reservoirs of strain diversity that may impact inflammatory disease and can be extended to other microbiome-associated diseases.

Analyzing microbial evolution through gene and genome phylogenies

Microbiome scientists critically need modern tools to explore and analyze microbial evolution. Often this involves studying the evolution of microbial genomes as a whole. However, different genes in a single genome can be subject to different evolutionary pressures, which can result in distinct gene-level evolutionary histories. To address this challenge, we propose to treat estimated gene-level phylogenies as data objects, and present an interactive method for the analysis of a collection of gene phylogenies. We use a local linear approximation of phylogenetic tree space to visualize estimated gene trees as points in low-dimensional Euclidean space, and address important practical limitations of existing related approaches, allowing an intuitive visualization of complex data objects. We demonstrate the utility of our proposed approach through microbial data analyses, including by identifying outlying gene histories in strains of Prevotella, and by contrasting Streptococcus phylogenies estimated using different gene sets. Our method is available as an open-source R package, and assists with estimating, visualizing, and interacting with a collection of bacterial gene phylogenies.

Protein-Coding Gene Families in Prokaryote Genome Comparisons

The identification of orthologous genes is relevant for comparative genomics, phylogenetic analysis, and functional annotation. There are many computational tools for the prediction of orthologous groups as well as web-based resources that offer orthology datasets for download and online analysis. This chapter presents a simple and practical guide to the process of orthologous group prediction, using a dataset of 10 prokaryotic proteomes as example. The orthology methods covered are OrthoMCL, COGtriangles, OrthoFinder2, and OMA. The authors compare the number of orthologous groups predicted by these various methods, and present a brief workflow for the functional annotation and reconstruction of phylogenies from inferred single-copy orthologous genes. The chapter also demonstrates how to explore two orthology databases: eggNOG6 and OrthoDB.

The mitogenomes characterization of two Peltigera species (Peltigera elisabethae and Peltigera polydactylon) and comparative mitogenomic analyses of six Peltigera

In the present study, the mitochondrial genomes of Peltigera elisabethae and P. polydactylon were sequenced and assembled. The two mitogenomes were composed of circular DNA molecules, with sizes of 64,034 bp and 59,208 bp, respectively. Comparative analysis showed that the genome size, GC content, GC skew, and AT skew varied between the two mitochondrial genomes. In codon analysis, phenylalanine (Phe), isoleucine (Ile), and leucine (Leu) were most frequently used in six Peltigera genomes. Evolutionary analysis showed that all 14 protein-coding genes (PCGs) were subject to purifying selection in the six Peltigera species. Regarding gene rearrangement, the PCGs of Peltigera had the same gene sequence and gene content, and a few intron sequences and spacer sequences were rearranged in Peltigera. In the phylogenetic analysis, we used Bayesian and ML methods to construct a phylogenetic tree. Two phylogenetic trees with consistent topology with high support indicate that mitochondrial genes were reliable molecular markers for analyzing the phylogenetic relationships. The present study enriches the mitochondrial genome data of Peltigera and promotes further understanding of the genetics and evolution of the Peltigera genus.

VBCG: 20 validated bacterial core genes for phylogenomic analysis with high fidelity and resolution

BACKGROUND

Phylogenomic analysis has become an inseparable part of studies of bacterial diversity and evolution, and many different bacterial core genes have been collated and used for phylogenomic tree reconstruction. However, these genes have been selected based on their presence and single-copy ratio in all bacterial genomes, leaving out the gene's 'phylogenetic fidelity' unexamined.

RESULTS

From 30,522 complete genomes covering 11,262 species, we examined 148 bacterial core genes that have been previously used for phylogenomic analysis. In addition to the gene presence and single-copy rations, we evaluated the gene's phylogenetic fidelity by comparing each gene's phylogeny with its corresponding 16S rRNA gene tree. Out of the 148 bacterial genes, 20 validated bacterial core genes (VBCG) were selected as the core gene set with the highest bacterial phylogenetic fidelity. Compared to the larger gene set, the 20-gene core set resulted in more species having all genes present and fewer species with missing data, thereby enhancing the accuracy of phylogenomic analysis. Using Escherichia coli strains as examples of prominent bacterial foodborne pathogens, we demonstrated that the 20 VBCG produced phylogenies with higher fidelity and resolution at species and strain levels while 16S rRNA gene tree alone could not.

CONCLUSION

The 20 validated core gene set improves the fidelity and speed of phylogenomic analysis. Among other uses, this tool improves our ability to explore the evolution, typing and tracking of bacterial strains, such as human pathogens. We have developed a Python pipeline and a desktop graphic app (available on GitHub) for users to perform phylogenomic analysis with high fidelity and resolution. Video Abstract.

Bradyrhizobium ottawaense efficiently reduces nitrous oxide through high nosZ gene expression

N2O is an important greenhouse gas influencing global warming, and agricultural land is the predominant (anthropogenic) source of N2O emissions. Here, we report the high N2O-reducing activity of Bradyrhizobium ottawaense, suggesting the potential for efficiently mitigating N2O emission from agricultural lands. Among the 15 B. ottawaense isolates examined, the N2O-reducing activities of most (13) strains were approximately five-fold higher than that of Bradyrhizobium diazoefficiens USDA110T under anaerobic conditions. This robust N2O-reducing activity of B. ottawaense was confirmed by N2O reductase (NosZ) protein levels and by mitigation of N2O emitted by nodule decomposition in laboratory system. While the NosZ of B. ottawaense and B. diazoefficiens showed high homology, nosZ gene expression in B. ottawaense was over 150-fold higher than that in B. diazoefficiens USDA110T, suggesting the high N2O-reducing activity of B. ottawaense is achieved by high nos expression. Furthermore, we examined the nos operon transcription start sites and found that, unlike B. diazoefficiens, B. ottawaense has two transcription start sites under N2O-respiring conditions, which may contribute to the high nosZ expression. Our study indicates the potential of B. ottawaense for effective N2O reduction and unique regulation of nos gene expression towards the high performance of N2O mitigation in the soil.

Metabolic resource overlap impacts competition among phyllosphere bacteria

The phyllosphere is densely colonised by microbial communities, despite sparse and heterogeneously distributed resources. The limitation of resources is expected to drive bacterial competition resulting in exclusion or coexistence based on fitness differences and resource overlap between individual colonisers. We studied the impact of resource competition by determining the effects of different bacterial colonisers on the growth of the model epiphyte Pantoea eucalypti 299R (Pe299R). Resource overlap was predicted based on genome-scale metabolic modelling. By combining results of metabolic modelling and pairwise competitions in the Arabidopsis thaliana phyllosphere and in vitro, we found that ten resources sufficed to explain fitness of Pe299R. An effect of both resource overlap and phylogenetic relationships was found on competition outcomes in vitro as well as in the phyllosphere. However, effects of resource competition were much weaker in the phyllosphere when compared to in vitro experiments. When investigating growth dynamics and reproductive success at the single-cell resolution, resource overlap and phylogenetic relationships are only weakly correlated with epiphytic Pe299R reproductive success, indicating that the leaf's spatial heterogeneity mitigates resource competition. Although the correlation is weak, the presence of competitors led to the development of Pe299R subpopulations that experienced different life histories and cell divisions. In some in planta competitions, Pe299R benefitted from the presence of epiphytes despite high resource overlap to the competitor strain suggesting other factors having stronger effects than resource competition. This study provides fundamental insights into how bacterial communities are shaped in heterogeneous environments and a framework to predict competition outcomes.

Analyzing microbial evolution through gene and genome phylogenies

Microbiome scientists critically need modern tools to explore and analyze microbial evolution. Often this involves studying the evolution of microbial genomes as a whole. However, different genes in a single genome can be subject to different evolutionary pressures, which can result in distinct gene-level evolutionary histories. To address this challenge, we propose to treat estimated gene-level phylogenies as data objects, and present an interactive method for the analysis of a collection of gene phylogenies. We use a local linear approximation of phylogenetic tree space to visualize estimated gene trees as points in low-dimensional Euclidean space, and address important practical limitations of existing related approaches, allowing an intuitive visualization of complex data objects. We demonstrate the utility of our proposed approach through microbial data analyses, including by identifying outlying gene histories in strains of Prevotella, and by contrasting Streptococcus phylogenies estimated using different gene sets. Our method is available as an open-source R package, and assists with estimating, visualizing and interacting with a collection of bacterial gene phylogenies. dimension reduction, microbiome, non-Euclidean, statistical genetics, visualization.

A microcystin synthesis mcyE/ndaF gene assay enables early detection of microcystin production in a tropical wastewater pond

Cyanobacteria can dominate the algal community in wastewater ponds, which can lead to the production of cyanotoxins and their release into the environment. We applied traditional and molecular techniques to identify cyanotoxin hazards and high-risk periods in a tropical wastewater treatment system. Potentially toxic cyanobacteria were identified by microscopy and amplicon sequencing over the course of a year. Toxin gene levels were monitored and compared to toxin production to identify likely toxin producing species and high-risk periods. Cyanobacteria were persistent in the effluent year-round, with Planktothrix and Microcystis the most abundant genera; Microcystis could not be resolved beyond genus using amplicon sequencing, but M. flos-aquae was identified as a dominant species by microscopy. Microcystin toxin was detected for the first time in treated effluent at the beginning of the wet season (December 2018), which correlated with an increase in Microcystis amplicon sequence abundance and elevated microcystin toxin gene (mcyE/ndaF) levels. Concomitantly, microscopy data showed an increase in M. flos-aquae but not M. aeruginosa. These data informed a refined sampling campaign in 2019 and results showed a strong correlation between mcyE/ndaF gene abundance, microcystin toxin levels and Microcystis amplicon sequence abundance. Microscopy data showed that in addition to M. flos-aquae, M. aeruginosa was also abundant in February and March 2019, with highest levels coinciding with toxin detection and toxin gene levels. M. aeruginosa was the most abundant Microcystis species detected in selected treated effluent samples by metagenomics analysis, and elevated levels coincided with toxin production. All microcystin genes in the biosynthesis pathway were detected, but microcystin genes from Planktothrix agardhii were not detected. Gene toxin assays were successfully used to predict microcystin production in this wastewater system. Changes in amplicon sequence relative abundance were a useful indicator of changes in the cyanobacterial community. We found that metagenomics was useful not just for identifying the most abundant Microcystis species, but the detection of microcystin biosynthesis genes helped confirm this genus as the most likely toxin producer in this system. We recommend toxin gene testing for the early detection of potential toxin producing cyanobacteria to manage the risk of toxicity and allow the implementation of risk management strategies.

Ancient Rapid Radiation Explains Most Conflicts Among Gene Trees and Well-Supported Phylogenomic Trees of Nostocalean Cyanobacteria

Prokaryotic genomes are often considered to be mosaics of genes that do not necessarily share the same evolutionary history due to widespread horizontal gene transfers (HGTs). Consequently, representing evolutionary relationships of prokaryotes as bifurcating trees has long been controversial. However, studies reporting conflicts among gene trees derived from phylogenomic data sets have shown that these conflicts can be the result of artifacts or evolutionary processes other than HGT, such as incomplete lineage sorting, low phylogenetic signal, and systematic errors due to substitution model misspecification. Here, we present the results of an extensive exploration of phylogenetic conflicts in the cyanobacterial order Nostocales, for which previous studies have inferred strongly supported conflicting relationships when using different concatenated phylogenomic data sets. We found that most of these conflicts are concentrated in deep clusters of short internodes of the Nostocales phylogeny, where the great majority of individual genes have low resolving power. We then inferred phylogenetic networks to detect HGT events while also accounting for incomplete lineage sorting. Our results indicate that most conflicts among gene trees are likely due to incomplete lineage sorting linked to an ancient rapid radiation, rather than to HGTs. Moreover, the short internodes of this radiation fit the expectations of the anomaly zone, i.e., a region of the tree parameter space where a species tree is discordant with its most likely gene tree. We demonstrated that concatenation of different sets of loci can recover up to 17 distinct and well-supported relationships within the putative anomaly zone of Nostocales, corresponding to the observed conflicts among well-supported trees based on concatenated data sets from previous studies. Our findings highlight the important role of rapid radiations as a potential cause of strongly conflicting phylogenetic relationships when using phylogenomic data sets of bacteria. We propose that polytomies may be the most appropriate phylogenetic representation of these rapid radiations that are part of anomaly zones, especially when all possible genomic markers have been considered to infer these phylogenies. [Anomaly zone; bacteria; horizontal gene transfer; incomplete lineage sorting; Nostocales; phylogenomic conflict; rapid radiation; Rhizonema.].

Hybridization breaks species barriers in long-term coevolution of a cyanobacterial population

Bacterial species often undergo rampant recombination yet maintain cohesive genomic identity. Ecological differences can generate recombination barriers between species and sustain genomic clusters in the short term. But can these forces prevent genomic mixing during long-term coevolution? Cyanobacteria in Yellowstone hot springs comprise several diverse species that have coevolved for hundreds of thousands of years, providing a rare natural experiment. By analyzing more than 300 single-cell genomes, we show that despite each species forming a distinct genomic cluster, much of the diversity within species is the result of hybridization driven by selection, which has mixed their ancestral genotypes. This widespread mixing is contrary to the prevailing view that ecological barriers can maintain cohesive bacterial species and highlights the importance of hybridization as a source of genomic diversity.

Unmasking of the von Willebrand A-domain surface adhesin CglB at bacterial focal adhesions mediates myxobacterial gliding motility

The predatory deltaproteobacterium Myxococcus xanthus uses a helically-trafficked motor at bacterial focal-adhesion (bFA) sites to power gliding motility. Using total internal reflection fluorescence and force microscopies, we identify the von Willebrand A domain-containing outer-membrane (OM) lipoprotein CglB as an essential substratum-coupling adhesin of the gliding transducer (Glt) machinery at bFAs. Biochemical and genetic analyses reveal that CglB localizes to the cell surface independently of the Glt apparatus; once there, it is recruited by the OM module of the gliding machinery, a heteroligomeric complex containing the integral OM β barrels GltA, GltB, and GltH, as well as the OM protein GltC and OM lipoprotein GltK. This Glt OM platform mediates the cell-surface accessibility and retention of CglB by the Glt apparatus. Together, these data suggest that the gliding complex promotes regulated surface exposure of CglB at bFAs, thus explaining the manner by which contractile forces exerted by inner-membrane motors are transduced across the cell envelope to the substratum.

Analysis of multipartite bacterial genomes using alignment free and alignment-based pipelines

Since the discovery of second chromosome in Rhodobacter sphaeroides 2.4.1 in 1989, multipartite genomes have been reported in over three hundred bacterial species under nine different phyla. This has shattered the unipartite (single chromosome) genome dogma in bacteria. Since then, many questions on various aspects of multipartite genomes in bacteria have been addressed. However, our understanding of how multipartite genomes emerge and evolve is still lacking. Importantly, the knowledge of genetic factors underlying the differences in multipartite and single-chromosome genomes is lacking. In this work, we have performed comparative evolutionary and functional genomics analyses to identify molecular factors that discriminate multipartite from unipartite bacteria, with the goal to decipher taxon-specific factors, and those that are prevalent across the taxa, underlying these traits. We assessed the roles of evolutionary mechanisms, specifically gene gain, in driving the divergence of bacteria with single and multiple chromosomes. In addition, we performed functional genomic analysis to garner support for our findings from comparative evolutionary analysis. We found genes such as those encoding conserved hypothetical proteins in Deinococcus radiodurans R1, and putative phage phi-C31 gp36 major capsid like and hypothetical proteins in Rhodobacter sphaeroides 2.4.1, which are located on accessory chromosomes in these bacteria but were not found in the inferred ancestral sequences, and on the primary chromosomes, as well as were not found in their closest relatives with single chromosome within the same clade. Our study shines a new light on the potential roles of the secondary chromosomes in helping bacteria with multipartite genomes to adapt to specialized environments or growth conditions.

Multi-genome metabolic modeling predicts functional inter-dependencies in the Arabidopsis root microbiome

BACKGROUND

From a theoretical ecology point of view, microbiomes are far more complex than expected. Besides competition and competitive exclusion, cooperative microbe-microbe interactions have to be carefully considered. Metabolic dependencies among microbes likely explain co-existence in microbiota.

METHODOLOGY

In this in silico study, we explored genome-scale metabolic models (GEMs) of 193 bacteria isolated from Arabidopsis thaliana roots. We analyzed their predicted producible metabolites under simulated nutritional constraints including "root exudate-mimicking growth media" and assessed the potential of putative metabolic exchanges of by- and end-products to avoid those constraints.

RESULTS

We found that the genome-encoded metabolic potential is quantitatively and qualitatively clustered by phylogeny, highlighting metabolic differentiation between taxonomic groups. Random, synthetic combinations of increasing numbers of strains (SynComs) indicated that the number of producible compounds by GEMs increased with average phylogenetic distance, but that most SynComs were centered around an optimal phylogenetic distance. Moreover, relatively small SynComs could reflect the capacity of the whole community due to metabolic redundancy. Inspection of 30 specific end-product metabolites (i.e., target metabolites: amino acids, vitamins, phytohormones) indicated that the majority of the strains had the genetic potential to produce almost all the targeted compounds. Their production was predicted (1) to depend on external nutritional constraints and (2) to be facilitated by nutritional constraints mimicking root exudates, suggesting nutrient availability and root exudates play a key role in determining the number of producible metabolites. An answer set programming solver enabled the identification of numerous combinations of strains predicted to depend on each other to produce these targeted compounds under severe nutritional constraints thus indicating a putative sub-community level of functional redundancy.

CONCLUSIONS

This study predicts metabolic restrictions caused by available nutrients in the environment. By extension, it highlights the importance of the environment for niche potential, realization, partitioning, and overlap. Our results also suggest that metabolic dependencies and cooperation among root microbiota members compensate for environmental constraints and help maintain co-existence in complex microbial communities. Video Abstract.

Binning Metagenomic Contigs Using Unsupervised Clustering and Reference Databases

Metagenomics can directly extract the genetic material of all microorganisms from the environment, and obtain metagenomic samples with a large number of unknown DNA sequences. Binning of metagenomic contigs is a hot topic in metagenomics research. There are two key challenges for the current unsupervised metagenomic clustering algorithms. First, unsupervised metagenomic clustering methods rarely use reference databases, causing a certain waste of resources. Second, unsupervised metagenomic clustering methods are restricted by the characteristics of the sequences and the clustering algorithms, and the binning effect is limited. Therefore, a new binning method for metagenomic contigs using unsupervised clustering methods and reference databases is proposed to address these challenges, to make full use of the advantages of unsupervised clustering methods and reference databases constructed by scientists to improve the overall binning effect. This method uses the integrated SVM classification model to further bin the unsupervised clustering parts that do not perform well. Our proposed method was tested on simulated datasets and a real dataset and compared with other state-of-the-art metagenomic clustering methods including CONCOCT, Metabin2.0, Autometa, and MetaBAT. The results show that our method can achieve higher precision rate and improve the binning effect.

Genomic analysis and biochemical profiling of an unaxenic strain of Synechococcus sp. isolated from the Peruvian Amazon Basin region

Cyanobacteria are diverse photosynthetic microorganisms able to produce a myriad of bioactive chemicals. To make possible the rational exploitation of these microorganisms, it is fundamental to know their metabolic capabilities and to have genomic resources. In this context, the main objective of this research was to determine the genome features and the biochemical profile of Synechococcus sp. UCP002. The cyanobacterium was isolated from the Peruvian Amazon Basin region and cultured in BG-11 medium. Growth parameters, genome features, and the biochemical profile of the cyanobacterium were determined using standardized methods. Synechococcus sp. UCP002 had a specific growth rate of 0.086 ± 0.008 μ and a doubling time of 8.08 ± 0.78 h. The complete genome of Synechococcus sp. UCP002 had a size of ∼3.53 Mb with a high coverage (∼200x), and its quality parameters were acceptable (completeness = 99.29%, complete and single-copy genes = 97.5%, and contamination = 0.35%). Additionally, the cyanobacterium had six plasmids ranging from 24 to 200 kbp. The annotated genome revealed ∼3,422 genes, ∼ 3,374 protein-coding genes (with ∼41.31% hypothetical protein-coding genes), two CRISPR Cas systems, and 61 non-coding RNAs. Both the genome and plasmids had the genes for prokaryotic defense systems. Additionally, the genome had genes coding the transcription factors of the metalloregulator ArsR/SmtB family, involved in sensing heavy metal pollution. The biochemical profile showed primary nutrients, essential amino acids, some essential fatty acids, pigments (e.g., all-trans-β-carotene, chlorophyll a, and phycocyanin), and phenolic compounds. In conclusion, Synechococcus sp. UCP002 shows biotechnological potential to produce human and animal nutrients and raw materials for biofuels and could be a new source of genes for synthetic biological applications.

Benefits of alignment quality-control processing steps and an Angiosperms353 phylogenomics pipeline applied to the Celastrales

We examined the impact of successive alignment quality-control steps on downstream phylogenomic analyses. We applied a recently published phylogenomics pipeline that was developed for the Angiosperms353 target-sequence-capture probe set to the flowering plant order Celastrales. Our final dataset consists of 158 species, including at least one exemplar from all 109 currently recognized Celastrales genera. We performed nine quality-control steps and compared the inferred resolution, branch support, and topological congruence of the inferred gene and species trees with those generated after each of the first six steps. We describe and justify each of our quality-control steps, including manual masking, in detail so that they may be readily applied to other lineages. We found that highly supported clades could generally be relied upon even if stringent orthology and alignment quality-control measures had not been applied. But separate instances were identified, for both concatenation and coalescence, wherein a clade was highly supported before manual masking but then subsequently contradicted. These results are generally reassuring for broad-scale analyses that use phylogenomics pipelines, but also indicate that we cannot rely exclusively on these analyses to conclude how challenging phylogenetic problems are best resolved.

A revisit to universal single-copy genes in bacterial genomes

Universal single-copy genes (USCGs) are widely used for species classification and taxonomic profiling. Despite many studies on USCGs, our understanding of USCGs in bacterial genomes might be out of date, especially how different the USCGs are in different studies, how well a set of USCGs can distinguish two bacterial species, whether USCGs can separate different strains of a bacterial species, to name a few. To fill the void, we studied USCGs in the most updated complete bacterial genomes. We showed that different USCG sets are quite different while coming from highly similar functional categories. We also found that although USCGs occur once in almost all bacterial genomes, each USCG does occur multiple times in certain genomes. We demonstrated that USCGs are reliable markers to distinguish different species while they cannot distinguish different strains of most bacterial species. Our study sheds new light on the usage and limitations of USCGs, which will facilitate their applications in evolutionary, phylogenomic, and metagenomic studies.

Characterization and genomic analysis of two novel psychrotolerant Acidithiobacillus ferrooxidans strains from polar and subpolar environments

The bioleaching process is carried out by aerobic acidophilic iron-oxidizing bacteria that are mainly mesophilic or moderately thermophilic. However, many mining sites are located in areas where the mean temperature is lower than the optimal growth temperature of these microorganisms. In this work, we report the obtaining and characterization of two psychrotolerant bioleaching bacterial strains from low-temperature sites that included an abandoned mine site in Chilean Patagonia (PG05) and an acid rock drainage in Marian Cove, King George Island in Antarctic (MC2.2). The PG05 and MC2.2 strains showed significant iron-oxidation activity and grew optimally at 20°C. Genome sequence analyses showed chromosomes of 2.76 and 2.84 Mbp for PG05 and MC2.2, respectively, and an average nucleotide identity estimation indicated that both strains clustered with the acidophilic iron-oxidizing bacterium Acidithiobacillus ferrooxidans. The Patagonian PG05 strain had a high content of genes coding for tolerance to metals such as lead, zinc, and copper. Concordantly, electron microscopy revealed the intracellular presence of polyphosphate-like granules, likely involved in tolerance to metals and other stress conditions. The Antarctic MC2.2 strain showed a high dosage of genes for mercury resistance and low temperature adaptation. This report of cold-adapted cultures of the At. ferrooxidans species opens novel perspectives to satisfy the current challenges of the metal bioleaching industry.

TCA cycle enhancement and uptake of monomeric substrates support growth of marine Roseobacter at low temperature

Members of the marine Roseobacter group are ubiquitous in global oceans, but their cold-adaptive strategies have barely been studied. Here, as represented by Loktanella salsilacus strains enriched in polar regions, we firstly characterized the metabolic features of a cold-adapted Roseobacter by multi-omics, enzyme activities, and carbon utilization procedures. Unlike in most cold-adapted microorganisms, the TCA cycle is enhanced by accumulating more enzyme molecules, whereas genes for thiosulfate oxidation, sulfate reduction, nitrate reduction, and urea metabolism are all expressed at lower abundance when L. salsilacus was growing at 5 °C in comparison with higher temperatures. Moreover, a carbon-source competition experiment has evidenced the preferential use of glucose rather than sucrose at low temperature. This selective utilization is likely to be controlled by the carbon source uptake and transformation steps, which also reflects an economic calculation balancing energy production and functional plasticity. These findings provide a mechanistic understanding of how a Roseobacter member and possibly others as well counteract polar constraints.

The metabolic adaptation of Loktanella salsilacus strains to cold involves an increase of enzymes involved in the TCA cycle and preferential use of glucose rather than sucrose at low temperature, providing insights into how Roseobacter adapts in polar regions.

StrainXpress: strain aware metagenome assembly from short reads

Next-generation sequencing–based metagenomics has enabled to identify microorganisms in characteristic habitats without the need for lengthy cultivation. Importantly, clinically relevant phenomena such as resistance to medication, virulence or interactions with the environment can vary already within species. Therefore, a major current challenge is to reconstruct individual genomes from the sequencing reads at the level of strains, and not just the level of species. However, strains of one species can differ only by minor amounts of variants, which makes it difficult to distinguish them. Despite considerable recent progress, related approaches have remained fragmentary so far. Here, we present StrainXpress, as a comprehensive solution to the problem of strain aware metagenome assembly from next-generation sequencing reads. In experiments, StrainXpress reconstructs strain-specific genomes from metagenomes that involve up to >1000 strains and proves to successfully deal with poorly covered strains. The amount of reconstructed strain-specific sequence exceeds that of the current state-of-the-art approaches by on average 26.75% across all data sets (first quartile: 18.51%, median: 26.60%, third quartile: 35.05%).

Phylogenomic Analysis of Metagenome-Assembled Genomes Deciphered Novel Acetogenic Nitrogen-Fixing Bathyarchaeota from Hot Spring Sediments

This study describes the phylogenomic analysis and metabolic insights of metagenome-assembled genomes (MAGs) retrieved from hot spring sediment samples. The metagenome-assembled sequences recovered three near-complete genomes belonging to the archaeal phylum. Analysis of genome-wide core genes and 16S rRNA-based phylogeny placed the ILS200 and ILS300 genomes within the uncultivated and largely understudied bathyarchaeal phylum, whereas ILS100 represented the phylum Thaumarchaeota. The average nucleotide identity (ANI) of the bin ILS100 was 76% with Nitrososphaeria_archaeon_isolate_SpSt-1069. However, the bins ILS200 and ILS300 showed ANI values of 75% and 70% with Candidatus_Bathyarchaeota_archaeon_isolate_DRTY-6_2_bin_115 and Candidatus_Bathyarchaeota_archaeon_BA1_ba1_01, respectively. The genomic potential of Bathyarchaeota bins ILS200 and ILS300 showed genes necessary for the Wood-Ljungdahl pathway, and the gene encoding the methyl coenzyme M reductase (mcr) complex essential for methanogenesis was absent. The metabolic potential of the assembled genomes included genes involved in nitrogen assimilation, including nitrogenase and the genes necessary for the urea cycle. The presence of these genes suggested the metabolic potential of Bathyarchaeota to fix nitrogen under extreme environments. In addition, the ILS200 and ILS300 genomes carried genes involved in the tricarboxylic acid (TCA) cycle, glycolysis, and degradation of organic carbons. Finally, we conclude that the reconstructed Bathyarchaeota bins are autotrophic acetogens and organo-heterotrophs.

IMPORTANCE We describe the Bathyarchaeota bins that are likely to be acetogens with a wide range of metabolic potential. These bins did not exhibit methanogenic machinery, suggesting methane production may not occur by all subgroup lineages of Bathyarchaeota. Phylogenetic analysis support that both ILS200 and ILS300 belonged to the Bathyarchaeota. The discovery of new bathyarchaeotal MAGs provides additional knowledge for understanding global carbon and nitrogen metabolism under extreme conditions.

Comparative Genomics of Synechococcus elongatus Explains the Phenotypic Diversity of the Strains

Strains of the freshwater cyanobacterium Synechococcus elongatus were first isolated approximately 60 years ago, and PCC 7942 is well established as a model for photosynthesis, circadian biology, and biotechnology research. The recent isolation of UTEX 3055 and subsequent discoveries in biofilm and phototaxis phenotypes suggest that lab strains of S. elongatus are highly domesticated. We performed a comprehensive genome comparison among the available genomes of S. elongatus and sequenced two additional laboratory strains to trace the loss of native phenotypes from the standard lab strains and determine the genetic basis of useful phenotypes. The genome comparison analysis provides a pangenome description of S. elongatus, as well as correction of extensive errors in the published sequence for the type strain PCC 6301. The comparison of gene sets and single nucleotide polymorphisms (SNPs) among strains clarifies strain isolation histories and, together with large-scale genome differences, supports a hypothesis of laboratory domestication. Prophage genes in laboratory strains, but not UTEX 3055, affect pigmentation, while unique genes in UTEX 3055 are necessary for phototaxis. The genomic differences identified in this study include previously reported SNPs that are, in reality, sequencing errors, as well as SNPs and genome differences that have phenotypic consequences. One SNP in the circadian response regulator rpaA that has caused confusion is clarified here as belonging to an aberrant clone of PCC 7942, used for the published genome sequence, that has confounded the interpretation of circadian fitness research.

Multidrug resistance from a one health perspective in Ethiopia: A systematic review and meta-analysis of literature (2015–2020)

Purpose

The emergence of antimicrobial resistance is a major global health challenge and becoming an urgent priority for policymakers. There is a paucity of scientific studies presenting the multidrug resistance pattern from one health perspective in Ethiopia. Therefore, a systematic review and meta-analysis aimed to determine the pooled prevalence of multidrug resistance in bacteria from human, animal, food, and environmental sources.

Methods

In this systematic review and meta-analysis, an electronic search was made in PubMed & Google scholar using different keywords. The studies conducted in all areas of Ethiopia, published from 2015 to 2020 in peer-reviewed journals, English full-length papers were included. The meta-analysis was done on STATA version 14. The pooled prevalence of multidrug resistance for each bacterium was analysed using the random-effects model; Cochran Q statistics and the I² statistic was used to analyse heterogeneity and considered significant at p < 0.01.

Results

81 studies were included in the systematic review and meta-analysis; 53 human studies, eight animal studies, and 16 environments/food studies. The meta-analysis included six species from gram-positive bacteria and 13 from gram-negative bacteria. S. aureus 53% (95%CI: 42–64%), Coagulase negative Staphylococci 68%(95%CI:53–82), Pseudomonas spp. 73%(95%CI:48–93%), E. coli 70% (95%CI:61–78%), Citrobacter spp. 71%(95%CI:54–87%), Klebsiella spp. 68% (54–80%), Enterobacter spp. 67% (48–83%) and Salmonella spp. 65% (95%CI:48–81%) were the common multidrug-resistant species of bacteria from two or more sources.

Conclusion

In Ethiopia, the pooled prevalence of MDR is high in most bacterial species from humans, animals, food, and environmental sources. Staphylococcus, most members of the Enterobacteriaceae and Pseudomonas, are the standard MDR bacterial population involving all sources. Therefore, integrated policy and intervention measures should be implemented to reduce the emergence and spread of MDR bacteria for better animal and human health outcomes.

Metagenomic strain detection with SameStr: identification of a persisting core gut microbiota transferable by fecal transplantation

BACKGROUND

The understanding of how microbiomes assemble, function, and evolve requires metagenomic tools that can resolve microbiota compositions at the strain level. However, the identification and tracking of microbial strains in fecal metagenomes is challenging and available tools variably classify subspecies lineages, which affects their applicability to infer microbial persistence and transfer.

RESULTS

We introduce SameStr, a bioinformatic tool that identifies shared strains in metagenomes by determining single-nucleotide variants (SNV) in species-specific marker genes, which are compared based on a maximum variant profile similarity. We validated SameStr on mock strain populations, available human fecal metagenomes from healthy individuals and newly generated data from recurrent Clostridioides difficile infection (rCDI) patients treated with fecal microbiota transplantation (FMT). SameStr demonstrated enhanced sensitivity to detect shared dominant and subdominant strains in related samples (where strain persistence or transfer would be expected) when compared to other tools, while being robust against false-positive shared strain calls between unrelated samples (where neither strain persistence nor transfer would be expected). We applied SameStr to identify strains that are stably maintained in fecal microbiomes of healthy adults over time (strain persistence) and that successfully engraft in rCDI patients after FMT (strain engraftment). Taxonomy-dependent strain persistence and engraftment frequencies were positively correlated, indicating that a specific core microbiota of intestinal species is adapted to be competitive both in healthy microbiomes and during post-FMT microbiome assembly. We explored other use cases for strain-level microbiota profiling, as a metagenomics quality control measure and to identify individuals based on the persisting core gut microbiota.

CONCLUSION

SameStr provides for a robust identification of shared strains in metagenomic sequence data with sufficient specificity and sensitivity to examine strain persistence, transfer, and engraftment in human fecal microbiomes. Our findings identify a persisting healthy adult core gut microbiota, which should be further studied to shed light on microbiota contributions to chronic diseases. Video abstract.

Comparative Genome Analysis of ‘Candidatus Phytoplasma luffae’ Reveals the Influential Roles of Potential Mobile Units in Phytoplasma Evolution

Phytoplasmas are insect-transmitted plant pathogens that cause substantial losses in agriculture. In addition to economic impact, phytoplasmas induce distinct disease symptoms in infected plants, thus attracting attention for research on molecular plant-microbe interactions and plant developmental processes. Due to the difficulty of establishing an axenic culture of these bacteria, culture-independent genome characterization is a crucial tool for phytoplasma research. However, phytoplasma genomes have strong nucleotide composition biases and are repetitive, which make it challenging to produce complete assemblies. In this study, we utilized Illumina and Oxford Nanopore sequencing technologies to obtain the complete genome sequence of ‘Candidatus Phytoplasma luffae’ strain NCHU2019 that is associated with witches’ broom disease of loofah (Luffa aegyptiaca) in Taiwan. The fully assembled circular chromosome is 769 kb in size and is the first representative genome sequence of group 16SrVIII phytoplasmas. Comparative analysis with other phytoplasmas revealed that NCHU2019 has a remarkably repetitive genome, possessing a pair of 75 kb repeats and at least 13 potential mobile units (PMUs) that account for ∼25% of its chromosome. This level of genome repetitiveness is exceptional for bacteria, particularly among obligate pathogens with reduced genomes. Our genus-level analysis of PMUs demonstrated that these phytoplasma-specific mobile genetic elements can be classified into three major types that differ in gene organization and phylogenetic distribution. Notably, PMU abundance explains nearly 80% of the variance in phytoplasma genome sizes, a finding that provides a quantitative estimate for the importance of PMUs in phytoplasma genome variability. Finally, our investigation found that in addition to horizontal gene transfer, PMUs also contribute to intra-genomic duplications of effector genes, which may provide redundancy for subfunctionalization or neofunctionalization. Taken together, this work improves the taxon sampling for phytoplasma genome research and provides novel information regarding the roles of mobile genetic elements in phytoplasma evolution.

Computational analyses of bacterial strains from shotgun reads

Shotgun sequencing is routinely employed to study bacteria in microbial communities. With the vast amount of shotgun sequencing reads generated in a metagenomic project, it is crucial to determine the microbial composition at the strain level. This study investigated 20 computational tools that attempt to infer bacterial strain genomes from shotgun reads. For the first time, we discussed the methodology behind these tools. We also systematically evaluated six novel-strain-targeting tools on the same datasets and found that BHap, mixtureS and StrainFinder performed better than other tools. Because the performance of the best tools is still suboptimal, we discussed future directions that may address the limitations.

MetaCRS: unsupervised clustering of contigs with the recursive strategy of reducing metagenomic dataset's complexity

Background

Metagenomics technology can directly extract microbial genetic material from the environmental samples to obtain their sequencing reads, which can be further assembled into contigs through assembly tools. Clustering methods of contigs are subsequently applied to recover complete genomes from environmental samples. The main problems with current clustering methods are that they cannot recover more high-quality genes from complex environments. Firstly, there are multiple strains under the same species, resulting in assembly of chimeras. Secondly, different strains under the same species are difficult to be classified. Thirdly, it is difficult to determine the number of strains during the clustering process.

Results

In view of the shortcomings of current clustering methods, we propose an unsupervised clustering method which can improve the ability to recover genes from complex environments and a new method for selecting the number of sample’s strains in clustering process. The sequence composition characteristics (tetranucleotide frequency) and co-abundance are combined to train the probability model for clustering. A new recursive method that can continuously reduce the complexity of the samples is proposed to improve the ability to recover genes from complex environments. The new clustering method was tested on both simulated and real metagenomic datasets, and compared with five state-of-the-art methods including CONCOCT, Maxbin2.0, MetaBAT, MyCC and COCACOLA. In terms of the number and quality of recovered genes from metagenomic datasets, the results show that our proposed method is more effective.

Conclusions

A new contigs clustering method is proposed, which can recover more high-quality genes from complex environmental samples.

Investigation of fiber utilization in the rumen of dairy cows based on metagenome-assembled genomes and single-cell RNA sequencing

BACKGROUND

Dairy cows utilize human-inedible, low-value plant biomass to produce milk, a low-cost product with rich nutrients and high proteins. This process largely relies on rumen microbes that ferment lignocellulose and cellulose to produce volatile fatty acids (VFAs). The VFAs are absorbed and partly metabolized by the stratified squamous rumen epithelium, which is mediated by diverse cell types. Here, we applied a metagenomic binning approach to explore the individual microbes involved in fiber digestion and performed single-cell RNA sequencing on rumen epithelial cells to investigate the cell subtypes contributing to VFA absorption and metabolism.

RESULTS

The 52 mid-lactating dairy cows in our study (parity = 2.62 ± 0.91) had milk yield of 33.10 ± 6.72 kg. We determined the fiber digestion and fermentation capacities of 186 bacterial genomes using metagenomic binning and identified specific bacterial genomes with strong cellulose/xylan/pectin degradation capabilities that were highly associated with the biosynthesis of VFAs. Furthermore, we constructed a rumen epithelial single-cell map consisting of 18 rumen epithelial cell subtypes based on the transcriptome of 20,728 individual epithelial cells. A systematic survey of the expression profiles of genes encoding candidates for VFA transporters revealed that IGFBP5+ cg-like spinous cells uniquely highly expressed SLC16A1 and SLC4A9, suggesting that this cell type may play important roles in VFA absorption. Potential cross-talk between the microbiome and host cells and their roles in modulating the expression of key genes in the key rumen epithelial cell subtypes were also identified.

CONCLUSIONS

We discovered the key individual microbial genomes and epithelial cell subtypes involved in fiber digestion, VFA uptake and metabolism, respectively, in the rumen. The integration of these data enables us to link microbial genomes and epithelial single cells to the trophic system. Video abstract.

Shared features and reciprocal complementation of the Chlamydomonas and Arabidopsis microbiota

Microscopic algae release organic compounds to the region immediately surrounding their cells, known as the phycosphere, constituting a niche for colonization by heterotrophic bacteria. These bacteria take up algal photoassimilates and provide beneficial functions to their host, in a process that resembles the establishment of microbial communities associated with the roots and rhizospheres of land plants. Here, we characterize the microbiota of the model alga Chlamydomonas reinhardtii and reveal extensive taxonomic and functional overlap with the root microbiota of land plants. Using synthetic communities derived from C. reinhardtii and Arabidopsis thaliana, we show that phycosphere and root bacteria assemble into taxonomically similar communities on either host. We show that provision of diffusible metabolites is not sufficient for phycosphere community establishment, which additionally requires physical proximity to the host. Our data suggest the existence of shared ecological principles driving the assembly of the A. thaliana root and C. reinhardtii phycosphere microbiota, despite the vast evolutionary distance between these two photosynthetic organisms.

Phylogeny and potential virulence of cryptic clade Escherichia coli species complex isolates derived from an arable field trial

Analysis of Escherichia coli taxonomy has expanded into a species-complex with the identification of divergent cryptic clades. A key question is the evolutionary trajectory of these clades and their relationship to isolates of clinical or veterinary importance. Since they have some environmental association, we screened a collection of E. coli isolated from a long-term spring barley field trial for their presence. While most isolates clustered into the enteric-clade, four of them clustered into Clade-V, and one in Clade-IV. The Clade -V isolates shared >96% intra-clade average nucleotide sequence identity but <91% with other clades. Although pan-genomics analysis confirmed their taxonomy as Clade -V (E. marmotae), retrospective phylogroup PCR did not discriminate them correctly. Differences in metabolic and adherence gene alleles occurred in the Clade -V isolates compared to E. coli sensu scricto. They also encoded the bacteriophage phage-associated cyto-lethal distending toxin (CDT) and antimicrobial resistance (AMR) genes, including an ESBL, blaOXA-453. Thus, the isolate collection encompassed a genetic diversity, and included cryptic clade isolates that encode potential virulence factors. The analysis has determined the phylogenetic relationship of cryptic clade isolates with E. coli sensu scricto and indicates a potential for horizontal transfer of virulence factors.

Phylogenetic Signal, Congruence, and Uncertainty across Bacteria and Archaea

Reconstruction of the Tree of Life is a central goal in biology. Although numerous novel phyla of bacteria and archaea have recently been discovered, inconsistent phylogenetic relationships are routinely reported, and many inter-phylum and inter-domain evolutionary relationships remain unclear. Here, we benchmark different marker genes often used in constructing multidomain phylogenetic trees of bacteria and archaea and present a set of marker genes that perform best for multidomain trees constructed from concatenated alignments. We use recently-developed Tree Certainty metrics to assess the confidence of our results and to obviate the complications of traditional bootstrap-based metrics. Given the vastly disparate number of genomes available for different phyla of bacteria and archaea, we also assessed the impact of taxon sampling on multidomain tree construction. Our results demonstrate that biases between the representation of different taxonomic groups can dramatically impact the topology of resulting trees. Inspection of our highest-quality tree supports the division of most bacteria into Terrabacteria and Gracilicutes, with Thermatogota and Synergistota branching earlier from these superphyla. This tree also supports the inclusion of the Patescibacteria within the Terrabacteria as a sister group to the Chloroflexota instead of as a basal-branching lineage. For the Archaea, our tree supports three monophyletic lineages (DPANN, Euryarchaeota, and TACK/Asgard), although we note the basal placement of the DPANN may still represent an artifact caused by biased sequence composition. Our findings provide a robust and standardized framework for multidomain phylogenetic reconstruction that can be used to evaluate inter-phylum relationships and assess uncertainty in conflicting topologies of the Tree of Life.

Genomic insights into the biosynthesis and physiology of the cyanobacterial neurotoxin 2,4-diaminobutanoic acid (2,4-DAB)

Cyanobacteria are an ancient clade of photosynthetic prokaryotes, whose worldwide occurrence, especially in water, presents health hazards to humans and animals due to the production of a range of toxins (cyanotoxins). These include the sometimes co-occurring, non-encoded diaminoacid neurotoxins 2,4-diaminobutanoic acid (2,4-DAB) and its structural analogue β-N-methylaminoalanine (BMAA). Knowledge of the biosynthetic pathway for 2,4-DAB, and its role in cyanobacteria, is lacking. The aspartate 4-phosphate pathway is a known route of 2,4-DAB biosynthesis in other bacteria and in some plant species. Another pathway to 2,4-DAB has been described in Lathyrus species. Here, we use bioinformatics analyses to investigate hypotheses concerning 2,4-DAB biosynthesis in cyanobacteria. We assessed the presence or absence of each enzyme in candidate biosynthesis routes, the aspartate 4-phosphate pathway and a pathway to 2,4-DAB derived from S-adenosyl-L-methionine (SAM), in 130 cyanobacterial genomes using sequence alignment, profile hidden Markov models, substrate specificity/active site identification and the reconstruction of gene phylogenies. In the aspartate 4-phosphate pathway, for the 18 species encoding diaminobutanoate-2-oxo-glutarate transaminase, the co-localisation of genes encoding the transaminase with the downstream decarboxylase or ectoine synthase - often within hybrid non-ribosomal peptide synthetase (NRPS)-polyketide synthases (PKS) clusters, NRPS-independent siderophore (NIS) clusters and incomplete ectoine clusters - is compatible with the hypothesis that some cyanobacteria use the aspartate 4-phosphate pathway for 2,4-DAB production. Through this route, in cyanobacteria, 2,4-DAB may be functionally associated with environmental iron-scavenging, via the production of siderophores of the schizokinen/synechobactin type and of some polyamines. In the pathway to 2,4-DAB derived from SAM, eight cyanobacterial species encode homologs of SAM-dependent 3-amino-3-carboxypropyl transferases. Other enzymes in this pathway have not yet been purified or sequenced. Ultimately, the biosynthesis of 2,4-DAB appears to be either restricted to some cyanobacterial species, or there may be multiple and additional routes, and roles, for the synthesis of this neurotoxin.

Gut microbiome drives individual memory variation in bumblebees

The potential of the gut microbiome as a driver of individual cognitive differences in natural populations of animals remains unexplored. Here, using metagenomic sequencing of individual bumblebee hindguts, we find a positive correlation between the abundance of Lactobacillus Firm-5 cluster and memory retention on a visual discrimination task. Supplementation with the Firm-5 species Lactobacillus apis, but not other non-Firm-5 bacterial species, enhances bees' memory. Untargeted metabolomics after L. apis supplementation show increased LPA (14:0) glycerophospholipid in the haemolymph. Oral administration of the LPA increases long-term memory significantly. Based on our findings and metagenomic/metabolomic analyses, we propose a molecular pathway for this gut-brain interaction. Our results provide insights into proximate and ultimate causes of cognitive differences in natural bumblebee populations.

Algibacter onchidii sp. nov., a symbiotic bacterium isolated from a marine invertebrate

A novel symbiotic bacterium, designated strain XY-114^T, was isolated from the cerata of an Onchidium marine invertebrate species collected in the South China Sea. Strain XY-114^T was an aerobic, Gram-stain-negative, non-motile and short rod-shaped bacterium (0.5-0.8 µm wide and 1.0-1.5 µm long) without flagellum. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain XY-114^T belonged to the genus Algibacter with the highest similarity of 97.2 % to the closest phylogenetic relative Algibacter aestuarii KYW371^T. Cells grew at 15-37 °C (optimum, 30 °C), at pH 5.5-9.0 (optimum 7.0-8.0) and at NaCl concentrations of 0.5-5.0 % (w/v; optimum 1.5-3.0 %). The major fatty acids (>10 %) were summed feature 3 (comprising C_16 : 1  ω7c and/or C_16 : 1  ω6c), iso-C_15 : 0, iso-C_15 : 1 G and iso-C_17 : 0 3-OH. The predominant polar lipid was phosphatidylethanolamine. The predominant respiratory quinone was MK-6. Flexirubin-type pigments were absent. The genome size of strain XY-114^T was 3.4 Mbp, with 34.9 mol% of DNA G+C content. The average nucleotide identity, digital DNA-DNA hybridization and amino acid identity values between strain XY-114^T and A. aestuarii KYW371^T were 74.5 %, 17.0±1.8 % and 73.9 %. Characterization based on phylogenetic, phenotypic, chemotaxonomic and genomic evidence demonstrated that strain XY-114^T represents a novel species of the genus Algibacter, for which the name Algibacter onchidii sp. nov. is proposed. The type strain is XY-114^T (=KCTC 72217^T=MCCC 1K03606^T).

Prokaryotic Genome Annotation

In the last decade, the high-throughput and relatively low cost of short-read sequencing technologies have revolutionized prokaryotic genomics. This has led to an exponential increase in the number of bacterial and archaeal genome sequences available, as well as corresponding increase of genome assembly and annotation tools developed. Together, these hardware and software technologies have given scientists unprecedented options to study their chosen microbial systems without the need for large teams of bioinformaticists or supercomputing facilities. While these analysis tools largely fall into only a few categories, each may have different requirements, caveats and file formats, and some may be rarely updated or even abandoned. And so, despite the apparent ease in sequencing and analyzing a prokaryotic genome, it is no wonder that the budding genomicist may quickly find oneself overwhelmed. Here, we aim to provide the reader with an overview of genome annotation and its most important considerations, as well as an easy-to-follow protocol to get started with annotating a prokaryotic genome.

Draft genome and description of Waterburya agarophytonicola gen. nov. sp. nov. (Pleurocapsales, Cyanobacteria): a seaweed symbiont

This work introduces Waterburya agarophytonicola Bonthond and Shalygin gen. nov., sp. nov, a baeocyte producing cyanobacterium that was isolated from the rhodophyte Agarophyton vermiculophyllum (Ohmi) Gurgel et al., an invasive seaweed that has spread across the northern hemisphere. The new species genome reveals a diverse repertoire of chemotaxis and adhesion related genes, including genes coding for type IV pili assembly proteins and a high number of genes coding for filamentous hemagglutinin family (FHA) proteins. Among a genetic basis for the synthesis of siderophores, carotenoids and numerous vitamins, W. agarophytonicola is potentially capable of producing cobalamin (vitamin B₁₂), for which A. vermiculophyllum is an auxotroph. With a taxonomic description of the genus and species and a draft genome, this study provides as a basis for future research, to uncover the nature of this geographically independent association between seaweed and cyanobiont.

Recovery of strain-resolved genomes from human microbiome through an integration framework of single-cell genomics and metagenomics

BACKGROUND

Obtaining high-quality (HQ) reference genomes from microbial communities is crucial for understanding the phylogeny and function of uncultured microbes in complex microbial ecosystems. Despite improvements in bioinformatic approaches to generate curated metagenome-assembled genomes (MAGs), existing metagenome binners obtain population consensus genomes but they are nowhere comparable to genomes sequenced from isolates in terms of strain level resolution. Here, we present a framework for the integration of single-cell genomics and metagenomics, referred to as single-cell (sc) metagenomics, to reconstruct strain-resolved genomes from microbial communities at once.

RESULTS

Our sc-metagenomics integration framework, termed SMAGLinker, uses single-cell amplified genomes (SAGs) generated using microfluidic technology as binning guides and integrates them with metagenome-assembled genomes (MAGs) to recover improved draft genomes. We compared sc-metagenomics with the metagenomics-alone approach using conventional metagenome binners. The sc-metagenomics approach showed precise contig binning and higher recovery rates (>97%) of rRNA and plasmids than conventional metagenomics in genome reconstruction from the cell mock community. In human microbiota samples, sc-metagenomics recovered the largest number of genomes with a total of 103 gut microbial genomes (21 HQ, with 65 showing >90% completeness) and 45 skin microbial genomes (10 HQ, with 40 showing >90% completeness), respectively. Conventional metagenomics recovered one Staphylococcus hominis genome, whereas sc-metagenomics recovered two S. hominis genomes from identical skin microbiota sample. Single-cell sequencing revealed that these S. hominis genomes were derived from two distinct strains harboring specifically different plasmids. We found that all conventional S. hominis MAGs had a substantial lack or excess of genome sequences and contamination from other Staphylococcus species (S. epidermidis).

CONCLUSIONS

SMAGLinker enabled us to obtain strain-resolved genomes in the mock community and human microbiota samples by assigning metagenomic sequences correctly and covering both highly conserved genes such as rRNA genes and unique extrachromosomal elements, including plasmids. SMAGLinker will provide HQ genomes that are difficult to obtain using metagenomics alone and will facilitate the understanding of microbial ecosystems by elucidating detailed metabolic pathways and horizontal gene transfer networks. SMAGLinker is available at https://github.com/kojiari/smaglinker . Video abstract.

Phylogenetic systematics of Butyrivibrio and Pseudobutyrivibrio genomes illustrate vast taxonomic diversity, open genomes and an abundance of carbohydrate-active enzyme family isoforms

Butyrivibrio and Pseudobutyrivibrio dominate in anaerobic gastrointestinal microbiomes, particularly the rumen, where they play a key role in harvesting dietary energy. Within these genera, five rumen species have been classified (Butyrivibrio fibrisolvens, Butyrivibrio hungatei, Butyrivibrio proteoclasticus, Pseudobutyrivibrio ruminis and Pseudobutyrivibrio xylanivorans) and more recently an additional Butyrivibrio sp. group was added. Given the recent increase in available genomes, we re-investigated the phylogenetic systematics and evolution of Butyrivibrio and Pseudobutyrivibrio. Across 71 genomes, we show using 16S rDNA and 40 gene marker phylogenetic trees that the current six species designations (P. ruminis, P. xylanivorans, B. fibrisolvens, Butyrivibrio sp., B. hungatei and B. proteclasticus) are found. However, pangenome analysis showed vast genomic variation and a high abundance of accessory genes (91.50–99.34 %), compared with core genes (0.66–8.50 %), within these six taxonomic groups, suggesting incorrectly assigned taxonomy. Subsequent pangenome accessory genomes under varying core gene cut-offs (%) and average nucleotide identity (ANI) analysis suggest the existence of 42 species within 32 genera. Pangenome analysis of those that still group within B. fibrisolvens, B. hungatei and P. ruminis, based on revised ANI phylogeny, also showed possession of very open genomes, illustrating the diversity that exists even within these groups. All strains of both Butyrivibrio and Pseudobutyrivibrio also shared a broad range of clusters of orthologous genes (COGs) (870), indicating recent evolution from a common ancestor. We also demonstrate that the carbohydrate-active enzymes (CAZymes) predominantly belong to glycosyl hydrolase (GH)2, 3, 5, 13 and 43, with numerous within family isoforms apparent, likely facilitating metabolic plasticity and resilience under dietary perturbations. This study provides a major advancement in our functional and evolutionary understanding of these important anaerobic bacteria.

Muricauda onchidii sp. nov., isolated from a marine invertebrate from South China Sea, and transfers of Flagellimonas algicola, Flagellimonas pacifica and Flagellimonas maritima to Muricauda algicola comb. nov., Muricauda parva nom. nov. and Muricauda aurantiaca nom. nov., respectively, and emended description of the genus Muricauda

An aerobic, Gram-stain-negative, rod-shaped and non-motile strain (XY-359^T) was isolated from the mouth of a marine invertebrate Onchidium species from the South China Sea. It grew at pH 6.0-8.5 (optimum, pH 7.5), at 15-37 °C (optimum, 30 °C) and in the presence of 0.5-4.5 % (w/v) NaCl (optimum, 2.5 %). It could not hydrolyse Tweens 20, 40, 60 or 80 and no flexirubin-type pigments were produced. The major polar lipids were phosphatidylethanolamine, one unidentified aminolipid, six unidentified phospholipids and two unidentified polar lipids. The major fatty acids were iso-C_17:0 3-OH, iso-C_15:1 G and iso-C_15:0 3-OH. The respiratory quinone was MK-6. Strain XY-359^T showed the greatest degree of 16S rRNA sequence similarity to Flagellimonas algicola AsT0115^T (96.54 %), followed by Muricauda flava DSM 22638^T (96.27 %). Phylogenetic analysis based on 16S rRNA gene sequences and 31 core genes indicated that strain XY-359^T belongs to the genus Muricauda. The genome size of strain XY-359^T was 4 207 872 bp, with 39.1 mol% of DNA G+C content. The average nucleotide identity and digital DNA-DNA hybridization values between strain XY-359^T and F. algicola AsT0115^T were 74.58 % and 18.5 %, respectively, and those between strain XY-359^T and M. flava DSM 22638^T were 74.2 % and 18.3 %. The combined phenotypic, chemotaxonomic and phylogenetic data suggest that strain XY-359^T represents a novel species of the genus Muricauda, for which the name Muricauda onchidii sp. nov. is proposed. The type strain is XY-359^T (=MCCC 1K03658^T =KCTC 72218^T). Moreover, based on the proposal of nesting Spongiibacterium and Flagellimonas within Muricauda by García (Validation List No. 193) and the analyses of phylogenetic trees and average amino acid identities in this study, the transfers of F. algicola, F. pacifica and F. maritima to the genus Muricauda as Muricauda algicola comb. nov., Muricauda parva nom. nov. and M. aurantiaca nom. nov., respectively, are proposed, with an emended description of the genus Muricauda.

Dynamic Colonization of Microbes and Their Functions after Fecal Microbiota Transplantation for Inflammatory Bowel Disease

For fecal microbiota transplantation (FMT) to be successful in immune diseases like inflammatory bowel disease, it is assumed that therapeutic microbes and their beneficial functions and immune interactions must colonize a recipient patient and persist in sufficient quantity and for a sufficient period of time to produce a clinical benefit. Few studies, however, have comprehensively profiled the colonization and persistence of transferred microbes along with the transfer of their microbial functions and interactions with the host immune system. Using 16S, metagenomic, and immunoglobulin A (IgA) sequencing, we analyzed hundreds of longitudinal microbiome samples from a randomized controlled trial of 12 patients with ulcerative colitis who received fecal transplant or placebo for 12 weeks. We uncovered diverse competitive dynamics among donor and patient strains, showing that persistence of transferred microbes is far from static. Indeed, one patient experienced a dramatic loss of donor bacteria 10 weeks into the trial, coinciding with a bloom of pathogenic bacteria and worsening symptoms. We evaluated the transfer of microbial functions, including desired ones, such as butyrate production, and unintended ones, such as antibiotic resistance. By profiling bacteria coated with IgA, we identified bacteria associated with inflammation and found that microbial interactions with the host immune system can be transferred across people, which could play a role in gut microbiome therapeutics for immune-related diseases. Our findings shed light on the colonization dynamics of gut microbes and their functions in the context of FMT to treat a complex disease-information that may provide a foundation for developing more-targeted therapeutics. IMPORTANCE Fecal microbiota transplantation (FMT)-transferring fecal microbes from a healthy donor to a sick patient-has shown promise for gut diseases such as inflammatory bowel disease. Unlike pharmaceuticals, however, fecal transplants are complex mixtures of living organisms, which must then interact with the microbes and immune system of the recipient. We sought to understand these interactions by tracking the microbes of 12 inflammatory bowel disease patients who received fecal transplants for 12 weeks. We uncovered a range of dynamics. For example, one patient experienced successful transfer of donor bacteria, only to lose them after 10 weeks. We similarly evaluated transfer of microbial functions, including how they interacted with the recipient's immune system. Our findings shed light on the colonization dynamics of gut microbes, as well as their functions in the context of FMT-information that may provide a critical foundation for the development of more-targeted therapeutics.

Endozoicomonadaceae symbiont in gills of Acesta clam encodes genes for essential nutrients and polysaccharide degradation

Gammaproteobacteria from the family Endozoicomonadaceae have emerged as widespread associates of dense marine animal communities. Their abundance in coral reefs involves symbiotic relationships and possibly host nutrition. We explored functions encoded in the genome of an uncultured Endozoicomonadaceae 'Candidatus Acestibacter aggregatus' that lives inside gill cells of large Acesta excavata clams in deep-water coral reefs off mid-Norway. The dominance and deep branching lineage of this symbiont was confirmed using 16S rRNA gene sequencing and phylogenomic analysis from shotgun sequencing data. The 4.5 Mb genome binned in this study has a low GC content of 35% and is enriched in transposon and chaperone gene annotations indicating ongoing adaptation. Genes encoding functions potentially involved with the symbiosis include ankyrins, repeat in toxins, secretion and nutritional systems. Complete pathways were identified for the synthesis of eleven amino acids and six B-vitamins. A minimal chitinolytic machinery was indicated from a glycosyl hydrolase GH18 and a lytic polysaccharide monooxygenase LPMO10. Expression of the latter was confirmed using proteomics. Signal peptides for secretion were identified for six polysaccharide degrading enzymes, ten proteases and three lipases. Our results suggest a nutritional symbiosis fuelled by enzymatic products from extracellular degradation processes.

Prokaryotic taxonomy and nomenclature in the age of big sequence data

The classification of life forms into a hierarchical system (taxonomy) and the application of names to this hierarchy (nomenclature) is at a turning point in microbiology. The unprecedented availability of genome sequences means that a taxonomy can be built upon a comprehensive evolutionary framework, a longstanding goal of taxonomists. However, there is resistance to adopting a single framework to preserve taxonomic freedom, and ever increasing numbers of genomes derived from uncultured prokaryotes threaten to overwhelm current nomenclatural practices, which are based on characterised isolates. The challenge ahead then is to reach a consensus on the taxonomic framework and to adapt and scale the existing nomenclatural code, or create a new code, to systematically incorporate uncultured taxa into the chosen framework.

Tobacco Root Endophytic Arthrobacter Harbors Genomic Features Enabling the Catabolism of Host-Specific Plant Specialized Metabolites

Plant roots constitute the primary interface between plants and soilborne microorganisms and harbor microbial communities called the root microbiota. Recent studies have demonstrated a significant contribution of plant specialized metabolites (PSMs) to the assembly of root microbiota. However, the mechanistic and evolutionary details underlying the PSM-mediated microbiota assembly and its contribution to host specificity remain elusive. Here, we show that the bacterial genus Arthrobacter is predominant specifically in the tobacco endosphere and that its enrichment in the tobacco endosphere is partially mediated by a combination of two unrelated classes of tobacco-specific PSMs, santhopine and nicotine. We isolated and sequenced Arthrobacter strains from tobacco roots as well as soils treated with these PSMs and identified genomic features, including but not limited to genes for santhopine and nicotine catabolism, that are associated with the ability to colonize tobacco roots. Phylogenomic and comparative analyses suggest that these genes were gained in multiple independent acquisition events, each of which was possibly triggered by adaptation to particular soil environments. Taken together, our findings illustrate a cooperative role of a combination of PSMs in mediating plant species-specific root bacterial microbiota assembly and suggest that the observed interaction between tobacco and Arthrobacter may be a consequence of an ecological fitting process. IMPORTANCE Host secondary metabolites have a crucial effect on the taxonomic composition of its associated microbiota. It is estimated that a single plant species produces hundreds of secondary metabolites; however, whether different classes of metabolites have distinctive or common roles in the microbiota assembly remains unclear. Here, we show that two unrelated classes of secondary metabolites in tobacco play a cooperative role in the formation of tobacco-specific compositions of the root bacterial microbiota, which has been established as a consequence of independent evolutionary events in plants and bacteria triggered by different ecological effects. Our findings illustrate mechanistic and evolutionary aspects of the microbiota assembly that are mediated by an arsenal of plant secondary metabolites.

Degradation of diclofenac by new bacterial strains and its influence on the physiological status of cells

Diclofenac (DCF) is one of the most commonly utilized non-steroidal anti-inflammatory drugs (NSAIDs), which is known to pose an ecotoxicological threat. In this study, from activated sludge and contaminated soil, we isolated four new bacterial strains able to degrade DCF under mono-substrate and co-metabolic conditions with glucose supplementation. We found that the effectiveness of DCF removal is strictly strain-specific and the addition of the primary substrate is not always beneficial. To assess the multidirectional influence of DCF on bacterial cells we evaluated the alterations of increasing concentrations of this drug on membrane structure. A significant increase was observed in the content of 17:0 cyclo fatty acid, which is responsible for reduced fluidity and profound changes in membrane rigidity. The cell injury and oxidative stress were assessed with biomarkers used as endpoints of toxicity, i.e. catalase (CAT), superoxide dismutase (SOD), lipids peroxidation (LPX), and both intra- and extracellular alkaline and acid phosphatase activity. Results indicated that DCF induced oxidative stress, frequently intensified by the addition of glucose. However, the response of the microbial cells to the presence of DCF should not be generalized, since the overall picture of the particular alterations greatly varied for each of the examined strains.