Critical Assessment of Metagenome Interpretation: the second round of challenges.

Evaluating metagenomic software is key for optimizing metagenome interpretation and focus of the Initiative for the Critical Assessment of Metagenome Interpretation (CAMI). The CAMI II challenge engaged the community to assess methods on realistic and complex datasets with long- and short-read sequences, created computationally from around 1,700 new and known genomes, as well as 600 new plasmids and viruses. Here we analyze 5,002 results by 76 program versions. Substantial improvements were seen in assembly, some due to long-read data. Related strains still were challenging for assembly and genome recovery through binning, as was assembly quality for the latter. Profilers markedly matured, with taxon profilers and binners excelling at higher bacterial ranks, but underperforming for viruses and Archaea. Clinical pathogen detection results revealed a need to improve reproducibility. Runtime and memory usage analyses identified efficient programs, including top performers with other metrics. The results identify challenges and guide researchers in selecting methods for analyses.

Non-target analysis of Danish wastewater treatment plant effluent: Statistical analysis of chemical fingerprinting as a step toward a future monitoring tool.

In an attempt to discover and characterize the plethora of xenobiotic substances, this study investigates chemical compounds released into the environment with wastewater effluents. A novel non-targeted screening methodology based on ultra-high resolution Orbitrap mass spectrometry and nanoflow ultra-high performance liquid chromatography together with a newly optimized data-processing pipeline were applied to effluent samples from two state-of-the-art and one small wastewater treatment facility. In total, 785 molecular structures were obtained, of which 38 were identified as single compounds, while 480 structures were identified at a putative level. Most of these substances were therapeutics and drugs, present as parent compounds and metabolites. Using R packages Phyloseq and MetacodeR, originally developed for bioinformatics, significant differences in xenobiotic presence in the wastewater effluents between the three sites were demonstrated.

Cessation of grazing causes biodiversity loss and homogenization of soil food webs.

There is widespread concern that cessation of grazing in historically grazed ecosystems is causing biotic homogenization and biodiversity loss. We used 12 montane grassland sites along an 800 km north-south gradient across the UK, to test whether cessation of grazing affects local α- and ß-diversity of below-ground food webs. We show cessation of grazing leads to strongly decreased α-diversity of most groups of soil microbes and fauna, particularly of relatively rare taxa. By contrast, the ß-diversity varied between groups of soil organisms. While most soil microbial communities exhibited increased homogenization after cessation of grazing, we observed decreased homogenization for soil fauna after cessation of grazing. Overall, our results indicate that exclusion of domesticated herbivores from historically grazed montane grasslands has far-ranging negative consequences for diversity of below-ground food webs. This underscores the importance of grazers for maintaining the diversity of below-ground communities, which play a central role in ecosystem functioning.

Detection of nucleotide modifications in bacteria and bacteriophages: Strengths and limitations of current technologies and software.

RNA and DNA modifications occur in eukaryotes and prokaryotes, as well as in their viruses, and serve a wide range of functions, from gene regulation to nucleic acid protection. Although the first nucleotide modification was discovered almost 100 years ago, new and unusual modifications are still being described. Nucleotide modifications have also received more attention lately because of their increased significance, but also because new sequencing approaches have eased their detection. Chiefly, third generation sequencing platforms PacBio and Nanopore offer direct detection of modified bases by measuring deviations of the signals. These unusual modifications are especially prevalent in bacteriophage genomes, the viruses of bacteria, where they mostly appear to protect DNA against degradation from host nucleases. In this Opinion article, we highlight and discuss current approaches to detect nucleotide modifications, including hardwares and softwares, and look onward to future applications, especially for studying unusual, rare, or complex genome modifications in bacteriophages. The ability to distinguish between several types of nucleotide modifications may even shed new light on metagenomic studies.

Three novel Erwinia billingiae phages isolated from organic waste represent three new genera.

Despite the ecological significance of viral communities, phages remain insufficiently studied. Current genomic databases lack high-quality phage genome sequences linked to specific bacteria. Bacteria of the genus Erwinia are known to colonize the phyllosphere of plants, both as commensals and as pathogens. We isolated three Erwinia billingiae phages-Zoomie, Pecta, and Snitter-from organic household waste. Based on sequence similarity to their closest relatives, we propose that they represent three new genera: "Pectavirus" within the family Zobellviridae, "Snittervirus" in the subfamily Tempevirinae, family Drexlerviridae, and "Zoomievirus" within the family Autographiviridae, which, together with the genus Limelightvirus, may constitute a new subfamily.

Four novel Curtobacterium phages isolated from environmental samples.

Despite Curtobacterium spp. often being associated with the plant phyllosphere, i.e., the areal region of different plant species, only one phage targeting a member of the genus Curtobacterium has been isolated so far. In this study, we isolated four novel plaque-forming Curtobacterium phages, Reje, Penoan, Parvaparticeps, and Pize, with two novel Curtobacterium strains as propagation hosts. Based on the low nucleotide intergenomic similarity (<32.4%) between these four phages and any phage with a genome sequence in the NCBI database, we propose the establishment of the four genera, "Rejevirus", "Pizevirus", "Penoanvirus", and "Parvaparticepsvirus", all in the class of Caudoviricetes.

Salmonella phage akira, infecting selected Salmonella enterica Enteritidis and Typhimurium strains, represents a new lineage of bacteriophages.

Some serovars of Salmonella can cause life-threatening diarrhoeal diseases and bacteriemia. The emergence of multidrug-resistant strains has led to a need for alternative treatments such as phage therapy, which requires available, well-described, diverse, and suitable phages. Phage akira was found to lyse 19 out of 32 Salmonella enterica serovars and farm isolates tested, although plaque formation was observed with only two S. Enteritidis and one S. Typhimurium strain. Phage akira encodes anti-defence genes against type 1 R-M systems, is distinct (<65% nucleotide sequence identity) from related phages and has siphovirus morphology. We propose that akira represents a new genus in the class Caudoviricetes.

An improved direct metamobilome approach increases the detection of larger-sized circular elements across kingdoms.

Mobile genetic elements (MGEs) are instrumental in natural prokaryotic genome editing, permitting genome plasticity and allowing microbes to accumulate genetic diversity. MGEs serve as a vast communal gene pool and include DNA elements such as plasmids and bacteriophages (phages) among others. These mobile DNA elements represent a human health risk as they can introduce new traits, such as antibiotic resistance or virulence, to a bacterial strain. Sequencing libraries targeting environmental circular MGEs, referred to as metamobilomes, may broaden our current understanding of the mechanisms behind the mobility, prevalence and content of these elements. However, metamobilomics is affected by a severe bias towards small circular elements, introduced by multiple displacement amplification (MDA). MDA is typically used to overcome limiting DNA quantities after the removal of non-circular DNA during library preparations. By examining the relationship between sequencing coverage and the size of circular MGEs in paired metamobilome datasets with and without MDA, we show that larger circular elements are lost when using MDA. This study is the first to systematically demonstrate that MDA is detrimental to detecting larger-sized plasmids if small plasmids are present. It is also the first to show that MDA can be omitted when using enzyme-based DNA fragmentation and PCR in library preparation kits such as Nextera XT® from Illumina.

The effect of faecal microbiota transplantation on abdominal pain, stool frequency, and stool form in patients with moderate-to-severe irritable bowel syndrome: results from a randomised, double-blind, placebo-controlled study.

BACKGROUND: Irritable bowel syndrome (IBS) is associated with intestinal dysbiosis. Therefore, faecal microbiota transplantation (FMT) has been hypothesised to have a positive effect in patients with IBS. In this study, we analysed previously unexamined data from our randomised, double-blind, placebo-controlled study (trial registration number NCT02788071). The objective was to evaluate the effect of FMT on abdominal pain, stool frequency, and stool form. METHOD: The study included 52 adult patients with moderate-to-severe IBS assigned randomly to treatment with FMT capsules or placebo capsules (1:1) for 12 days. The patients were followed for a total of six months, during which they kept a daily symptom diary tracking their abdominal pain on a scale from 0-10 and their bowel movements using the Bristol Stool Form Scale (BSFS). Diary data were not collected before treatment start. RESULTS: A statistically significant improvement in stool frequency was found in the FMT group from during treatment to post-treatment and 1 month. No statistically significant differences were found between groups at any time during the study for any of abdominal pain, stool frequency, and stool form (as measured by weighted stool score). CONCLUSION: In this analysis of results from a randomised, double-blind, placebo-controlled study, we found no clinically beneficial effect of FMT on abdominal pain, stool frequency, or stool form. However, since the current literature on the potential role of FMT in treating IBS shows conflicting results, further studies are required. To assess treatment efficacy, we recommend future studies to include daily symptom diaries both before and after treatment intervention.

Enterococcus phage Nonaheksakonda infecting clinical isolates of Enterococcus faecalis represents a new lineage in the family Siphoviridae.

Enterococcus phage Nonaheksakonda was isolated from wastewater, using a vancomycin-resistant strain of the opportunistic pathogen Enterococcus faecalis (VRE) as a host. Nonaheksakonda is a lytic phage infecting E. faecalis V583 and clinical isolates with at least four different multi-locus sequence types (MLSTs). The genome is a 41.9-kb double-stranded DNA molecule (34.6% GC) with 74 coding sequences. Comparative analysis revealed only one close relative, Enterococcus phage heks. All other phages had low protein similarity and shared less than 54% nucleotide sequence identity with phage Nonaheksakonda. The most similar phages were all classified and unclassified efquatroviruses. We propose that the phages Nonaheksakonda and heks represent a novel genus within the family Siphoviridae, order Caudovirales, for which we propose the name "Nonaheksakondavirus".

Faecal virome transplantation decreases symptoms of type 2 diabetes and obesity in a murine model.

OBJECTIVE: Development of obesity and type 2 diabetes (T2D) are associated with gut microbiota (GM) changes. The gut viral community is predominated by bacteriophages (phages), which are viruses that attack bacteria in a host-specific manner. The antagonistic behaviour of phages has the potential to alter the GM. As a proof-of-concept, we demonstrate the efficacy of faecal virome transplantation (FVT) from lean donors for shifting the phenotype of obese mice into closer resemblance of lean mice. DESIGN: The FVT consisted of viromes with distinct profiles extracted from the caecal content of mice from different vendors that were fed a low-fat (LF) diet for 14 weeks. Male C57BL/6NTac mice were divided into five groups: LF (as diet control), high-fat (HF) diet, HF+ampicillin (Amp), HF+Amp+FVT and HF+FVT. At weeks 6 and 7 of the study, the HF+FVT and HF+Amp+FVT mice were treated with FVT by oral gavage. The Amp groups were treated with Amp 24 hours prior to first FVT treatment. RESULTS: Six weeks after first FVT, the HF+FVT mice showed a significant decrease in weight gain compared with the HF group. Further, glucose tolerance was comparable between the LF and HF+FVT mice, while the other HF groups all had impaired glucose tolerance. These observations were supported by significant shifts in GM composition, blood plasma metabolome and expression levels of genes associated with obesity and T2D development. CONCLUSIONS: Transfer of caecal viral communities from mice with a lean phenotype into mice with an obese phenotype led to reduced weight gain and normalised blood glucose parameters relative to lean mice. We hypothesise that this effect is mediated via FVT-induced GM changes.

Unravelling plasmidome distribution and interaction with its hosting microbiome.

Horizontal gene transfer via plasmids plays a pivotal role in microbial evolution. The forces that shape plasmidomes functionality and distribution in natural environments are insufficiently understood. Here, we present a comparative study of plasmidomes across adjacent microbial environments present in different individual rumen microbiomes. Our findings show that the rumen plasmidome displays enormous unknown functional potential currently unannotated in available databases. Nevertheless, this unknown functionality is conserved and shared with published rat gut plasmidome data. Moreover, the rumen plasmidome is highly diverse compared with the microbiome that hosts these plasmids, across both similar and different rumen habitats. Our analysis demonstrates that its structure is shaped more by stochasticity than selection. Nevertheless, the plasmidome is an active partner in its intricate relationship with the host microbiome with both interacting with and responding to their environment.

Critical Assessment of Metagenome Interpretation-a benchmark of metagenomics software.

Methods for assembly, taxonomic profiling and binning are key to interpreting metagenome data, but a lack of consensus about benchmarking complicates performance assessment. The Critical Assessment of Metagenome Interpretation (CAMI) challenge has engaged the global developer community to benchmark their programs on highly complex and realistic data sets, generated from ∼700 newly sequenced microorganisms and ∼600 novel viruses and plasmids and representing common experimental setups. Assembly and genome binning programs performed well for species represented by individual genomes but were substantially affected by the presence of related strains. Taxonomic profiling and binning programs were proficient at high taxonomic ranks, with a notable performance decrease below family level. Parameter settings markedly affected performance, underscoring their importance for program reproducibility. The CAMI results highlight current challenges but also provide a roadmap for software selection to answer specific research questions.

Faecal microbiota transplantation alters gut microbiota in patients with irritable bowel syndrome: results from a randomised, double-blind placebo-controlled study.

OBJECTIVE: IBS is associated with an intestinal dysbiosis and faecal microbiota transplantation (FMT) has been hypothesised to have a positive effect in patients with IBS. We performed a randomised, double-blind placebo-controlled trial to investigate if FMT resulted in an altered gut microbiota and improvement in clinical outcome in patients with IBS. DESIGN: We performed this study in 52 adult patients with moderate-to-severe IBS. At the screening visit, clinical history and symptoms were assessed and faecal samples were collected. Patients were randomised to FMT or placebo capsules for 12 days and followed for 6 months. Study visits were performed at baseline, 1, 3 and 6 months, where patients were asked to register their symptoms using the IBS-severity scoring system (IBS-SSS) and IBS-specific quality of life (IBS-QoL). Prior to each visit, faecal samples were collected. RESULTS: A significant difference in improvement in IBS-SSS score was observed 3 months after treatment (p=0.012) favouring placebo. This was similar for IBS-QoL data after 3 months (p=0.003) favouring placebo. Patients receiving FMT capsules had an increase in faecal microbial biodiversity while placebos did not. CONCLUSION: In this randomised double-blinded placebo-controlled study, we found that FMT changed gut microbiota in patients with IBS. But patients in the placebo group experienced greater symptom relief compared with the FMT group after 3 months. Altering the gut microbiota is not enough to obtain clinical improvement in IBS. However, different study designs and larger studies are required to examine the role of FMT in IBS. TRIAL REGISTRATION NUMBER: NCT02788071.

Groundwater contamination with 2,6-dichlorobenzamide (BAM) and perspectives for its microbial removal.

The pesticide metabolite 2,6-dichlorobenzamide (BAM) is very persistent in both soil and groundwater and has become one of the most frequently detected groundwater micropollutants. BAM is not removed by the physico-chemical treatment techniques currently used in drinking water treatment plants (DWTP); therefore, if concentrations exceed the legal threshold limit, it represents a sizeable problem for the stability and quality of drinking water production, especially in places that depend on groundwater for drinking water. Bioremediation is suggested as a valuable strategy for removing BAM from groundwater by deploying dedicated BAM-degrading bacteria in DWTP sand filters. Only a few bacterial strains with the capability to degrade BAM have been isolated, and of these, only three isolates belonging to the Aminobacter genus are able to mineralise BAM. Considerable effort has been made to elucidate degradation pathways, kinetics and degrader genes, and research has recently been presented on the application of strain Aminobacter sp. MSH1 for the purification of BAM-contaminated water. The aim of the present review was to provide insight into the issue of BAM contamination and to report on the current status and knowledge with regard to the application of microorganisms for purification of BAM-contaminated water resources. This paper discusses the prospects and challenges for bioaugmentation of DWTP sand filters with specific BAM-degrading bacteria and identifies relevant perspectives for future research.

Use of WGS data for investigation of a long-term NDM-1-producing Citrobacter freundii outbreak and secondary in vivo spread of blaNDM-1 to Escherichia coli, Klebsiella pneumoniae and Klebsiella oxytoca.

OBJECTIVES: An outbreak of NDM-1-producing Citrobacter freundii and possible secondary in vivo spread of blaNDM-1 to other Enterobacteriaceae were investigated. METHODS: From October 2012 to March 2015, meropenem-resistant Enterobacteriaceae were detected in 45 samples from seven patients at Aalborg University Hospital, Aalborg, Denmark. In silico resistance genes, Inc plasmid types and STs (MLST) were obtained from WGS data from 24 meropenem-resistant isolates (13 C. freundii, 6 Klebsiella pneumoniae, 4 Escherichia coli and 1 Klebsiella oxytoca) and 1 meropenem-susceptible K. oxytoca. The sequences of the meropenem-resistant C. freundii isolates were compared by phylogenetic analyses. In vitro susceptibility to 21 antimicrobial agents was tested. Furthermore, in vitro conjugation and plasmid characterization was performed. RESULTS: From the seven patients, 13 highly clonal ST18 NDM-1-producing C. freundii were isolated. The ST18 NDM-1-producing C. freundii isolates were only susceptible to tetracycline, tigecycline, colistin and fosfomycin (except for the C. freundii isolates from Patient 2 and Patient 7, which were additionally resistant to tetracycline). The E. coli and K. pneumoniae from different patients belonged to different STs, indicating in vivo transfer of blaNDM-1 in the individual patients. This was further supported by in vitro conjugation and detection of a 154 kb IncA/C2 plasmid with blaNDM-1. Patient screenings failed to reveal any additional cases. None of the patients had a history of recent travel abroad and the source of the blaNDM-1 plasmid was unknown. CONCLUSIONS: To our knowledge, this is the first report of an NDM-1-producing C. freundii outbreak and secondary in vivo spread of an IncA/C2 plasmid with blaNDM-1 to other Enterobacteriaceae.

Establishment of Bacterial Herbicide Degraders in a Rapid Sand Filter for Bioremediation of Phenoxypropionate-Polluted Groundwater.

In this study, we investigated the establishment of natural bacterial degraders in a sand filter treating groundwater contaminated with the phenoxypropionate herbicides (RS)-2-(4-chloro-2-methylphenoxy)propanoic acid (MCPP) and (RS)-2-(2,4-dichlorophenoxy)propanoic acid (DCPP) and the associated impurity/catabolite 4-chlorophenoxypropanoic acid (4-CPP). A pilot facility was set up in a contaminated landfill site. Anaerobic groundwater was pumped up and passed through an aeration basin and subsequently through a rapid sand filter, which is characterized by a short residence time of the water in the filter. For 3 months, the degradation of DCPP, MCPP, and 4-CPP in the sand filter increased to 15 to 30% of the inlet concentration. A significant selection for natural bacterial herbicide degraders also occurred in the sand filter. Using a most-probable-number (MPN) method, we found a steady increase in the number of culturable phenoxypropionate degraders, reaching approximately 5 × 10(5) degraders per g sand by the end of the study. Using a quantitative PCR targeting the two phenoxypropionate degradation genes, rdpA and sdpA, encoding stereospecific dioxygenases, a parallel increase was observed, but with the gene copy numbers being about 2 to 3 log units higher than the MPN. In general, the sdpA gene was more abundant than the rdpA gene, and the establishment of a significant population of bacteria harboring sdpA occurred faster than the establishment of an rdpA gene-carrying population. The identities of the specific herbicide degraders in the sand filter were assessed by Illumina MiSeq sequencing of 16S rRNA genes from sand filter samples and from selected MPN plate wells. We propose a list of potential degrader bacteria involved in herbicide degradation, including representatives belonging to the Comamonadaceae and Sphingomonadales.

Discrimination between native and Tn6010-associated oqxAB in Klebsiella spp., Raoultella spp., and other Enterobacteriaceae by using a two-step strategy.

We developed a two-step PCR-based strategy to detect genes encoding OqxAB, allowing a specific assignment of Tn6010-associated oqxAB in Enterobacteriaceae. Chromosomal location in this setup was confirmed by hybridization with I-CeuI-restricted genomes. This approach led us to find that Klebsiella sp. and Raoultella sp. reference strains chromosomally carried oqxAB.

High-resolution melt analysis for rapid comparison of bacterial community compositions.

In the study of bacterial community composition, 16S rRNA gene amplicon sequencing is today among the preferred methods of analysis. The cost of nucleotide sequence analysis, including requisite computational and bioinformatic steps, however, takes up a large part of many research budgets. High-resolution melt (HRM) analysis is the study of the melt behavior of specific PCR products. Here we describe a novel high-throughput approach in which we used HRM analysis targeting the 16S rRNA gene to rapidly screen multiple complex samples for differences in bacterial community composition. We hypothesized that HRM analysis of amplified 16S rRNA genes from a soil ecosystem could be used as a screening tool to identify changes in bacterial community structure. This hypothesis was tested using a soil microcosm setup exposed to a total of six treatments representing different combinations of pesticide and fertilization treatments. The HRM analysis identified a shift in the bacterial community composition in two of the treatments, both including the soil fumigant Basamid GR. These results were confirmed with both denaturing gradient gel electrophoresis (DGGE) analysis and 454-based 16S rRNA gene amplicon sequencing. HRM analysis was shown to be a fast, high-throughput technique that can serve as an effective alternative to gel-based screening methods to monitor microbial community composition.

Insights into the circular: The cryptic plasmidome and its derived antibiotic resistome in the urban water systems.

Plasmids have been a concern in the dissemination and evolution of antibiotic resistance in the environment. In this study, we investigated the total pool of plasmids (plasmidome) and its derived antibiotic resistance genes (ARGs) in different compartments of urban water systems (UWSs) in three European countries representing different antibiotic usage regimes. We applied a direct plasmidome approach using wet-lab methods to enrich circular DNA in the samples, followed by shotgun sequencing and in silico contig circularisation. We identified 9538 novel sequences in a total of 10,942 recovered circular plasmids. Of these, 66 were identified as conjugative, 1896 mobilisable and 8970 non-mobilisable plasmids. The UWSs' plasmidome was dominated by small plasmids (≤10 Kbp) representing a broad diversity of mobility (MOB) types and incompatibility (Inc) groups. A shared collection of plasmids from different countries was detected in all treatment compartments, and plasmids could be source-tracked in the UWSs. More than half of the ARGs-encoding plasmids carried mobility genes for mobilisation/conjugation. The richness and abundance of ARGs-encoding plasmids generally decreased with the flow, while we observed that non-mobilisable ARGs-harbouring plasmids maintained their abundance in the Spanish wastewater treatment plant. Overall, our work unravels that the UWS plasmidome is dominated by cryptic (i.e., non-mobilisable, non-typeable and previously unknown) plasmids. Considering that some of these plasmids carried ARGs, were prevalent across three countries and could persist throughout the UWSs compartments, these results should alarm and call for attention.