Long-read powered viral metagenomics in the oligotrophic Sargasso Sea.

Dominant microorganisms of the Sargasso Sea are key drivers of the global carbon cycle. However, associated viruses that shape microbial community structure and function are not well characterised. Here, we combined short and long read sequencing to survey Sargasso Sea phage communities in virus- and cellular fractions at viral maximum (80 m) and mesopelagic (200 m) depths. We identified 2,301 Sargasso Sea phage populations from 186 genera. Over half of the phage populations identified here lacked representation in global ocean viral metagenomes, whilst 177 of the 186 identified genera lacked representation in genomic databases of phage isolates. Viral fraction and cell-associated viral communities were decoupled, indicating viral turnover occurred across periods longer than the sampling period of three days. Inclusion of long-read data was critical for capturing the breadth of viral diversity. Phage isolates that infect the dominant bacterial taxa Prochlorococcus and Pelagibacter, usually regarded as cosmopolitan and abundant, were poorly represented.

Novel pelagiphage isolate Polarivirus skadi is a polar specialist that dominates SAR11-associated bacteriophage communities at high latitudes.

The SAR11 clade are the most abundant members of surface marine bacterioplankton and a critical component of global biogeochemical cycles. Similarly, pelagiphages that infect SAR11 are ubiquitous and highly abundant in the oceans. Pelagiphages are predicted to shape SAR11 community structures and increase carbon turnover throughout the oceans. Yet, ecological drivers of host and niche specificity of pelagiphage populations are poorly understood. Here we report the global distribution of a novel pelagiphage called "Polarivirus skadi", which is the sole representative of a novel genus. P. skadi was isolated from the Western English Channel using a cold-water ecotype of SAR11 as bait. P. skadi is closely related to the globally dominant pelagiphage HTVC010P. Along with other HTVC010P-type viruses, P. skadi belongs to a distinct viral family within the order Caudovirales, for which we propose the name Ubiqueviridae. Metagenomic read recruitment identified P. skadi as one of the most abundant pelagiphages on Earth. P. skadi is a polar specialist, replacing HTVC010P at high latitudes. Experimental evaluation of P. skadi host range against cold- and warm-water SAR11 ecotypes supported cold-water specialism. Relative abundance of P. skadi in marine metagenomes correlated negatively with temperature, and positively with nutrients, available oxygen, and chlorophyll concentrations. In contrast, relative abundance of HTVC010P correlated negatively with oxygen and positively with salinity, with no significant correlation to temperature. The majority of other pelagiphages were scarce in most marine provinces, with a few representatives constrained to discrete ecological niches. Our results suggest that pelagiphage populations persist within a global viral seed bank, with environmental parameters and host availability selecting for a few ecotypes that dominate ocean viromes.

Predicting outcomes following short-term ventricular assist device implant with the MELD-XI score.

BACKGROUND: Short-term continuous flow (STCF) ventricular assist devices (VADs) are utilized in adults with cardiogenic shock; however, mortality remains high. Previous studies have found that high pre-operative MELD-XI scores in durable VAD patients are associated with mortality. The use of the MELD-XI score to predict outcomes in STCF-VAD patients has not been explored. We sought to determine the relationship between MELD-XI and outcomes in adults with STCF-VADs. METHODS: This was a retrospective review of adults implanted with STCF-VADs between 2009 and 2019. Receiver operating characteristic (ROC) analysis was performed to predict outcomes and Kaplan-Meier analysis was done to assess survival. RESULTS: Seventy-nine patients were included with a median MELD-XI score of 21.2 (IQR 13.5, 27.0). Patients with an unsuccessful wean from support (p < 0.001) or major post-operative bleeding (p = 0.03) had significantly higher pre-implant MELD-XI scores. The optimal MELD-XI cut-point for mortality was 24.9 with 27.8 for major bleeding. Survival was worse among patients in the high-risk MELD-XI group, however, not statistically significant (p = 0.09). Prior ECMO support, but not MELD-XI, was an independent predictor of unsuccessful wean (p = 0.03). CONCLUSIONS: Pre-operative MELD-XI score was a moderate predictor of unsuccessful wean with limited utility in predicting bleeding in patients on STCF-VAD support. This scoring system may be useful in the clinical setting for pre-implant risk stratification and counseling among patients and outcomes.

Prospective examination of HLA sensitization after VAD implantation in children and adults.

BACKGROUND: Ventricular assist devices (VADs) have improved survival to heart transplantation (HTx). However, VADs have been associated with development of antibodies against human leukocyte antigen (HLA-Ab) which may limit the donor pool and decrease survival post-HTx. Since HLA-Ab development after VAD insertion is poorly understood, the purpose of this prospective single-center study was to quantify the incidence of and evaluate risk factors for HLA-Ab development across the age spectrum following VAD implantation. METHODS: Adult and pediatric patients undergoing VAD placement as bridge to transplant or transplant candidacy between 5/2016 and 7/2020 were enrolled. HLA-Ab were assessed pre-VAD and at 1-, 3-, and 12-months post-implant. Factors associated with HLA-Ab development post-VAD implant were explored using univariate and multivariate logistic regression. RESULTS: 15/41 (37%) adults and 7/17 (41%) children developed new HLA-Ab post-VAD. The majority of patients (19/22) developed HLA-Ab within two months of implant. New class I HLA-Ab were more common (87% adult, 86% pediatric). Prior pregnancy was strongly associated with HLA-Ab development in adults post-VAD (HR 16.7, 95% CI 1.8-158, p = 0.01). Of the patients who developed new HLA-Ab post-VAD, in 45% (10/22) the HLA-Ab resolved while in 55% (12/22) the HLA-Ab persisted. CONCLUSION: More than one-third of adult and pediatric VAD patients developed new HLA-Ab early after VAD implant with the majority having class I antibodies. Prior pregnancy was strongly associated with post-VAD HLA-Ab development. Further studies are needed to predict regression or persistence of HLA-Ab developed post-VAD, to understand modulation of individuals' immune responses to sensitizing events, and to determine whether transiently detected HLA-Ab post-VAD recur and have long-term clinical impact post-heart transplantation.

Left ventricular assist device inflow obstruction.

Inflow cannula obstruction is a rare complication of left ventricular assist device implantation. In this report, we present a case of inflow obstruction that was successfully treated with left ventricle myectomy and mitral valvectomy. Transesophageal echocardiogram was essential in diagnosing this condition.

Initial multicenter experience with ventricular assist devices in children and young adults with muscular dystrophy: An ACTION registry analysis.

PURPOSE: Cardiac disease results in significant morbidity and mortality in patients with muscular dystrophy (MD). Single centers have reported their ventricular assist device (VAD) experience in specific MDs and in limited numbers. This study sought to describe the outcomes associated with VAD therapy in an unselected population across multiple centers. METHODS: We examined outcomes of patients with MD and dilated cardiomyopathy implanted with a VAD at Advanced Cardiac Therapies Improving Outcomes Network (ACTION) centers from 9/2012 to 9/2020. RESULTS: A total of 19 VADs were implanted in 18 patients across 12 sites. The majority of patients had dystrophinopathy (66%) and the median age at implant was 17.2 years (range 11.7-29.5). Eleven patients were non-ambulatory (61%) and 6 (33%) were on respiratory support pre-VAD. Five (28%) patients were implanted as a bridge to transplant, 4 of whom survived to transplant. Of 13 patients implanted as bridge to decision or destination therapy, 77% were alive at 1 year and 69% at 2 years. The overall frequencies of positive outcome (transplanted or alive on device) at 1 year and 2 years were 84% and 78%, respectively. Two patients suffered a stroke, 2 developed sepsis, 1 required tracheostomy, and 1 experienced severe right heart failure requiring right-sided VAD. CONCLUSIONS: This study demonstrates the potential utility of VAD therapies in patients with muscular dystrophy. Further research is needed to further improve outcomes and better determine which patients may benefit most from VAD therapy in terms of survival and quality of life.

Cost-effectiveness of bivalirudin in pediatric ventricular assist devices.

BACKGROUND: Despite recent data suggesting improved outcomes with bivalirudin vs heparin in pediatric Ventricular assist devices (VAD), higher costs remain a barrier. This study quantified trends in bivalirudin use and compared outcomes, resource utilization, and cost-effectiveness associated with bivalirudin vs heparin. METHODS: Children age 0 to 6 year who received VAD from 2009 to 2021 were identified in Pediatric Health Information System. Bivalirudin use was evaluated using trend analysis and outcomes were compared using Fine-Gray subdistrubtion hazard ratios (SHR). Daily-level hospital costs were compared due to differences in length of stay. Cost-effectiveness was evaluated using incremental cost-effectiveness ratio (ICER). RESULTS: Of 691 pediatric VAD recipients (median age 1 year, IQR 0-2), 304 (44%) received bivalirudin with 90% receiving bivalirudin in 2021 (trend p-value <0.01). Bivalirudin had lower hospital mortality (26% vs 32%; adjusted SHR 0.57, 95% CI 0.40-0.83) driven by lower VAD mortality (20% vs 27%; adjusted SHR 0.46, 95% CI 0.32-0.77) after adjusting for year, age, diagnosis, and center VAD volume. Post-VAD length of stay was longer for bivalirudin than heparin (median 91 vs 64 days, respectively, p < 0.001). Median daily-level costs were lower among bivalirudin (cost ratio 0.87, 95% CI 0.79-0.96) with higher pharmacy costs offset by lower imaging, laboratory, supply, and room/board costs. Estimated ICER for bivalirudin vs heparin was $61,192 per quality-adjusted life year gained with a range of $27,673 to $131,243. CONCLUSIONS: Bivalirudin use significantly increased over the past decade and is now used in 90% young pediatric VAD recipients. Bivalirudin was associated with significantly lower hospital mortality and an ICER <$65,000, making it a cost-effective therapy for pediatric VAD recipients.

Ventricular assist device support following pediatric heart transplantation.

BACKGROUND: VAD support for early graft failure after HTx is a rare event in pediatrics. METHODS: We retrospectively describe our single-center experience with post-HTx VAD support in a cohort of patients transplanted between 01/05 and 12/20. RESULTS: Nine patients underwent VAD insertion in the early post-HTx period [median age 6.1 years (Range 0.3-20.3), median weight 17.6 kg (Range 3.5-65.0), and congenital heart disease (67%)]. Of the nine patients with early graft failure, almost half (44%) were implanted after 2015 and all of these patients had a pre-HTx plan for possible post-transplant VAD insertion. Time to VAD implant was a median of 0 day (Range 0-11). Total time on VAD support was a median of 12 days (Range 3.0-478.0). Two-thirds (n = 6; 67%) of the patients were weaned from support, retransplanted (11%) and two patients died (22%). In all of the patients where post-HTx VAD was anticipated there was 100% survival. CONCLUSIONS: In this small patient series, post-HTx VAD was a useful measure in selected patients especially with pre-HTx planning. However, more shared experiences to verify these findings are needed.

Decreasing driveline infections in patients supported on ventricular assist devices: a care pathway approach.

BACKGROUND: Driveline infections (DLIs) are a common adverse event in patients on ventricular assist devices (VADs) with incidence ranging from 14% to 59%. DLIs have an impact on patients and the healthcare system with efforts to prevent DLIs being essential. Prior to our intervention, our program had no standard driveline management presurgery and postsurgery. The purpose of this Quality Improvement (QI) initiative was to reduce DLIs and related admissions among patients with VAD within the first year post implant. METHODS: In anticipation of the QI project, we undertook a review of the programs' current driveline management procedures and completed a survey with patients with VAD to identify current barriers to proper driveline management. Retrospective data were collected for a pre-QI intervention baseline comparison group, which included adult patients implanted with a durable VAD between 1 January 2017 and 31 July 2018. A three-pronged care pathway (CP) was initiated among patients implanted during August 2018 to July 2019. The CP included standardised intraoperative, postoperative and predischarge teaching initiatives and tracking. Using statistical process control methods, DLIs and readmissions in the first year post implant were compared between patients in the CP group and non-CP patients. P-charts were used to detect special cause variation. RESULTS: A higher proportion of CP group patients developed a DLI in the first year after implant (52% vs 32%). None developed a DLI during the index admission, which differed from the non-CP group and met criteria for special cause variation. There was a downward trend in cumulative DLI-related readmissions among CP group patients (55% vs 67%). There was no association between CP compliance and development of DLIs within 1 year post implant. CONCLUSION: The CP did not lead to a reduction in the incidence of DLIs but there was a decrease in the proportion of patients with DLIs during their index admission and those readmitted for DLIs within 1 year post implant. This suggests that the CP played a role in decreasing the impact of DLIs in this patient population. However, given the short time period of follow-up longer follow-up will be required to look for sustained effects.

A Novel and Ubiquitous Marine Methylophage Provides Insights into Viral-Host Coevolution and Possible Host-Range Expansion in Streamlined Marine Heterotrophic Bacteria.

The methylotrophic OM43 clade are Gammaproteobacteria that comprise some of the smallest free-living cells known and have highly streamlined genomes. OM43 represents an important microbial link between marine primary production and remineralization of carbon back to the atmosphere. Bacteriophages shape microbial communities and are major drivers of mortality and global marine biogeochemistry. Recent cultivation efforts have brought the first viruses infecting members of the OM43 clade into culture. Here, we characterize a novel myophage infecting OM43 called Melnitz. Melnitz was isolated independently from water samples from a subtropical ocean gyre (Sargasso Sea) and temperate coastal (Western English Channel) systems. Metagenomic recruitment from global ocean viromes confirmed that Melnitz is globally ubiquitous, congruent with patterns of host abundance. Bacteria with streamlined genomes such as OM43 and the globally dominant SAR11 clade use riboswitches as an efficient method to regulate metabolism. Melnitz encodes a two-piece tmRNA (ssrA), controlled by a glutamine riboswitch, providing evidence that riboswitch use also occurs for regulation during phage infection of streamlined heterotrophs. Virally encoded tRNAs and ssrA found in Melnitz were phylogenetically more closely related to those found within the alphaproteobacterial SAR11 clade and their associated myophages than those within their gammaproteobacterial hosts. This suggests the possibility of an ancestral host transition event between SAR11 and OM43. Melnitz and a related myophage that infects SAR11 were unable to infect hosts of the SAR11 and OM43, respectively, suggesting host transition rather than a broadening of host range. IMPORTANCE Isolation and cultivation of viruses are the foundations on which the mechanistic understanding of virus-host interactions and parameterization of bioinformatic tools for viral ecology are based. This study isolated and characterized the first myophage known to infect the OM43 clade, expanding our knowledge of this understudied group of microbes. The nearly identical genomes of four strains of Melnitz isolated from different marine provinces and the global abundance estimations from metagenomic data suggest that this viral population is globally ubiquitous. Genome analysis revealed several unusual features in Melnitz and related genomes recovered from viromes, such as a curli operon and virally encoded tmRNA controlled by a glutamine riboswitch, neither of which are found in the host. Further phylogenetic analysis of shared genes indicates that this group of viruses infecting the gammaproteobacterial OM43 shares a recent common ancestor with viruses infecting the abundant alphaproteobacterial SAR11 clade. Host ranges are affected by compatible cell surface receptors, successful circumvention of superinfection exclusion systems, and the presence of required accessory proteins, which typically limits phages to singular narrow groups of closely related bacterial hosts. This study provides intriguing evidence that for streamlined heterotrophic bacteria, virus-host transitioning may not be necessarily restricted to phylogenetically related hosts but is a function of shared physical and biochemical properties of the cell.

Ventricular Assist Device Use in Patients With Single-Ventricle Circulation.

Ventricular assist devices (VADs) are being increasingly used to support patients with congenital heart disease and single-ventricle physiology. Because of their unique anatomy and physiology, special consideration must be used to provide effective mechanical circulatory support for each individual patient. This can include alternative cannulation techniques, strategies to balance cardiac output to the systemic and pulmonary circulations from a single ventricle, or the use of continuous vs pulsatile VADs for better ventricular offloading. In this article we review the etiology of single-ventricle failure, VAD options for support, cannulation strategies, post-VAD management considerations, and outcomes at each of the 3 stages of palliation.

Paracorporeal Support in Pediatric Patients: The Role of the Patient-Device Interaction.

BACKGROUND: Ventricular assist devices are important in the treatment of pediatric heart failure. Although paracorporeal pulsatile (PP) devices have historically been used, there has been increased use of paracorporeal continuous (PC) devices. We sought to compare the outcomes of children supported with a PP or PC, or combination of devices. METHODS: A retrospective review (2005 to 2019) was made of patients less than 19 years of age from a single center who received a PC, PP, or combination of devices. Patient characteristics were compared between device strategies, and Kaplan-Meier survival analysis was performed. RESULTS: Sixty-six patients were included: 62% male; 62% non-congenital heart disease; median age 0.9 years (interquartile range, 0.2 to 4.9); and median weight 8.5 kg (interquartile range, 4.3 to 17.7 kg). The PC devices were used in 45% of patients, PP in 35%, and a combination in 20%. Patients on PC devices had a lower median weight (P = .02) and a higher proportion of congenital heart disease (P = .02), and more patients required pre-ventricular assist device dialysis (P = .01). There was no difference in pre-ventricular assist device extracorporeal membrane oxygenation use (P = .15). There was a difference in survival among the three device strategies (P = .02). CONCLUSIONS: Differences in survival were evident, with patients on PC support having worse outcomes. Transition from PC to a PP devices was associated with a survival advantage. These findings may be driven by differences in patient characteristics across device strategies. Further studies are required to confirm these findings and to better understand the interaction between patient characteristics and device options.

Video Capsule Endoscopy in a Pediatric Patient With Hematemesis While on Ventricular Assist Device Support.

We report the first case of video capsule endoscopy usage to diagnose gastrointestinal bleeding in a pediatric patient on a ventricular assist device. The outcomes of this case are consistent with the findings of reports in adult patients, showing no patient complications, no pacemaker or ventricular assist device interactions, and successful identification of a gastrointestinal source of bleeding. Use of video capsule endoscopy in this patient changed the management plan and eliminated the need for further invasive investigations highlighting the potential utility of this diagnostic method in this patient population.

Human Leukocyte Antigen Antibody Sampling in Ventricular Assist Device Recipients: Are We Talking?

BACKGROUND: Ventricular assist devices (VADs) are commonly used as a bridge to transplantation but may yield HLA sensitization. We evaluated the prevalence of HLA antibody (Ab) sampling pre- and post-VAD placement in pediatric and adult patients and notification of VAD status to the HLA laboratory. METHODS: All pediatric and adult patients who received a first-time VAD between 2005 and 2013 were included in this single-center retrospective review. Data were collected from the University of Alberta Hospital histocompatibility laboratory's information system and a local VAD database. RESULTS: In total, 106 patients were included (40 pediatric, median 3.0 years [interquartile range, 0.3-10.7]; 66 adult, 55.0 years [46.8-61.2]). HLA Ab sampling within 1-month pre-VAD occurred in 70% of pediatric and 79% of adult recipients (P = .215). Testing within 1 month of VAD placement occurred in 89% of pediatric and 67% of adult recipients (P = .012). For those with HLA Ab sampling within 30 days postimplant, notification to the HLA laboratory of VAD status occurred in 19 of 27 (70%) pediatric and 24 of 33 (73%) adult patients (P = .533). Of patients transplanted post VAD with HLA Ab samples collected, 12 of 28 (43%) and 13 of 38 (34%) adult recipients did not have notification of VAD status to the HLA laboratory (P = .322). CONCLUSIONS: There were inconsistencies in HLA Ab sampling and communication to the HLA laboratory surrounding VAD placement. Standardization of both HLA Ab assessment frequency after VAD implantation and communication regarding changes in clinical status and the occurrence of key sensitizing events such as VAD placement are imperative as patients await transplantation.

Pediatric ventricular assist device registries: update and perspectives in the era of miniaturized continuous-flow pumps.

The success of ventricular assist devices (VADs) in the treatment of end-stage heart failure in the adult population has led to industrial innovation in VAD design, focusing on miniaturization and the reduction of complications. A byproduct of these innovations was that newer generation devices could have clinical applications in the pediatric population. Over the last decade, VAD usage in the pediatric population has increased dramatically, and the newer generation continuous flow (CF) devices have begun to supplant the older, pulsatile flow (PF) devices, formerly the sole option for ventricular assist in the pediatric population. However, despite the increase in VAD implants in the pediatric population, patient numbers remain low, and the need to share data between pediatric VAD centers has become that much more important for the continued growth of VAD programs worldwide. The creation of pediatric VAD registries, such as the Pediatric Registry for Mechanical Circulatory Support (PediMACS), the European Registry for Patients with Mechanical Circulatory Support (EUROMACS) and the Advanced Cardiac Therapies Improving Outcomes Network (ACTION) has enabled the collection of aggregate data from VAD centers worldwide, and provides a valuable resource for clinicians and programs, as more and more pediatric heart failure patients are considered candidates for VAD therapy.

Berlin Heart EXCOR and ACTION post-approval surveillance study report.

BACKGROUND: The Berlin Heart EXCOR Pediatric (EXCOR) ventricular assist device (VAD) was introduced in North America nearly 2 decades ago. The EXCOR was approved under Humanitarian Device Exemption status in 2011 and received post-market approval (PMA) in 2017 from Food and Drug Administration. Since the initial approval, the field of pediatric mechanical circulatory support has changed, specifically with regard to available devices, anticoagulation strategies, and the types of patients supported. This report summarizes the outcomes of patients supported with EXCOR from the Advanced Cardiac Therapies Improving Outcomes Network (ACTION) registry. These data were part of the PMA surveillance study (PSS) required by the Food and Drug Administration. METHODS: ACTION is a learning collaborative of over 40 pediatric heart failure programs worldwide, which collects data for all VAD implantations as one of its initiatives. All patients in North America with EXCOR implants reported to ACTION from 2018 to 2020 (n = 72) who had met an outcome were included in the EXCOR PSS group. This was compared with a historical, previously reported Berlin Heart EXCOR study group (Berlin Heart study [BHS] group, n = 320, 2007‒2014). RESULTS: Patients in the PSS group were younger, were smaller in weight/body surface area, were more likely to have congenital heart disease, and were less likely to receive a bi-VAD than those in the BHS group. Patients in the PSS group were less likely to be in Interagency Registry for Mechanically Assisted Circulatory Support Profile 1 and were supported for a longer duration. The primary anticoagulation therapy for 92% of patients in the PSS group was bivalirudin. Success, defined as being transplanted, being weaned for recovery, or being alive on a device at 180 days after implantation, was 86% in the PSS group compared with 76% in the BHS group. Incidence of stroke was reduced by 44% and the frequency of pump exchange by 40% in the PSS group compared with those in the BHS group. Similarly, all other adverse events, including major bleeding, were reduced in the PSS group. CONCLUSIONS: The PSS data, collected through ACTION, highlight the improvement in outcomes for patients supported with EXCOR compared with the outcomes in a historical cohort. These findings may be the result of changes in patient care practices over time and collaborative learning.

Draft Genome Sequences of Pelagimyophage Mosig EXVC030M and Pelagipodophage Lederberg EXVC029P, Isolated from Devil's Hole, Bermuda.

We present the genomes of two isolated bacteriophages infecting Pelagibacter ubique HTCC1062. Pelagibacter phage Mosig EXVC030M (Myoviridae) and Pelagibacter phage Lederberg EXVC029P (Podoviridae) were isolated by dilution-to-extinction culturing from the oxygen minimum zone at Devil's Hole (Harrington Sound, Bermuda).

Efficient dilution-to-extinction isolation of novel virus-host model systems for fastidious heterotrophic bacteria.

Microbes and their associated viruses are key drivers of biogeochemical processes in marine and soil biomes. While viruses of phototrophic cyanobacteria are well-represented in model systems, challenges of isolating marine microbial heterotrophs and their viruses have hampered experimental approaches to quantify the importance of viruses in nutrient recycling. A resurgence in cultivation efforts has improved the availability of fastidious bacteria for hypothesis testing, but this has not been matched by similar efforts to cultivate their associated bacteriophages. Here, we describe a high-throughput method for isolating important virus-host systems for fastidious heterotrophic bacteria that couples advances in culturing of hosts with sequential enrichment and isolation of associated phages. Applied to six monthly samples from the Western English Channel, we first isolated one new member of the globally dominant bacterial SAR11 clade and three new members of the methylotrophic bacterial clade OM43. We used these as bait to isolate 117 new phages, including the first known siphophage-infecting SAR11, and the first isolated phage for OM43. Genomic analyses of 13 novel viruses revealed representatives of three new viral genera, and infection assays showed that the viruses infecting SAR11 have ecotype-specific host ranges. Similar to the abundant human-associated phage ɸCrAss001, infection dynamics within the majority of isolates suggested either prevalent lysogeny or chronic infection, despite a lack of associated genes, or host phenotypic bistability with lysis putatively maintained within a susceptible subpopulation. Broader representation of important virus-host systems in culture collections and genomic databases will improve both our understanding of virus-host interactions, and accuracy of computational approaches to evaluate ecological patterns from metagenomic data.