BioTechniques

Quantitative polymerase chain reaction (qPCR) is limited in measuring absolute nucleic acid copy numbers due to the inherent variability of calibrators. Here, we introduce the Quantal PCR (quPCR), a novel method that eliminates the need for calibrators by defining an intrinsic quantal unit derived from the thermodynamic and kinetic properties of the replication system. This approach first determines amplification efficiency at high template concentrations, which is then used as the replication probability to construct quantification cycle (Cq) distribution profiles. These profiles are compared with those from limiting dilution PCR to derive the Cq value for the minimal quantal-replication unit ("quCq"), enabling calculation of the sample copy number. Validation using a dual-target DNA template showed near-identical copy numbers using two distinct target-specific replication systems. Thus, quPCR represents a new method for absolute nucleic acid quantification at the single-molecule level, offering a calibrator-free alternative for absolute quantification.

Precision-cut lung slices (PCLS) have emerged as a powerful tool for studying the biology of viable human lung tissue. However, the presence of agarose impurities compromises RNA yield and integrity during the extraction process. We tested whether using an alternative Plant kit RNA extraction method to wash agarose impurities or pre-dissolving agarose from PCLS implementing a dissolving buffer for routine RNA isolation in gel-electrophoresis would improve RNA quantity, quality, and integrity. Our results show that RNA quantity and integrity are highly compromised when using a conventional method of RNA extraction. The plant kit and dissolution of agarose increased the RNA quantity to 0.42{+/-}0.11 and 0.65{+/-}0.17 {micro}g/PCLS (measured by the Qubit) and integrity number to 6.60{+/-}0.59 and 9.13{+/-}0.39 (measured by the Bioanalyzer), respectively. The presence of impurities in conventional and Plant kit extractions misled to an overestimation of the RNA quantity and quality using the NanoDrop. The Plant kit and agarose dissolution showed a significant transcript integrity increase in GUSB (p<0.0001) and COL1A1 (p<0.05) expression, validating these methods over conventional extraction. We encourage laboratories applying PCLS experimentation to implement alternative methods to remove agarose impurities during RNA extraction, as well as to rely on sensitive quantitative techniques, such as the Qubit and Bioanalyzer, for RNA quantification and integrity measurements.

BackgroundDNA polymerase activity assays are required for enzyme quality control in biotechnology and diagnostics, but standard methods rely on specialist reagents, radioactivity and other hazardous materials, or real-time PCR instruments that are not widely accessible in resource-limited settings. This constrains local production of high quality, validated reagents and increases dependence on imported enzymes. MethodsBased on experiences derived from partnerships with scientists in several low and middle-income countries (LMICs) and stakeholder consultations, we adapted a commercial EvaGreen-based fluorometric DNA polymerase activity assay for isothermal operation using minimal equipment. Assay conditions were optimized using Design of Experiments (DOE) methodology, varying temperature, reaction volume, and MgCl2 concentration. To address reagent cost and supply-chain constraints, we developed detailed protocols for in-house synthesis of the off-patent AOAO-12 DNA dye (sold commercially as EvaGreen) and generation of single-stranded DNA templates via asymmetric PCR. ResultsOptimized isothermal assay conditions (40{degrees}C, 7.75 mM MgCl2) reliably quantified activity across multiple DNA polymerase families. In-house synthesized AOAO-12 dye exhibited comparable DNA-binding performance to commercial alternatives (R{superscript 2} = 0.95), reducing costs by more than an order of magnitude when normalized to working concentrations, enabling assay costs of approximately {pound}0.001 per reaction. The assay is effective across multiple polymerases (Bst-LF, OpenVent, Taq, Q5) and is compatible with both plate readers and qByte, a low-cost, open-source fluorometric device. ConclusionsThis stakeholder-informed assay provides an accessible, cost-effective solution for DNA polymerase quality control in resource-limited settings. The combination of optimized commercial protocols and in-house reagent synthesis offers flexibility for different resource contexts, potentially improving access to molecular biology tools globally.

Fluorescent in situ hybridization (FISH) enables highly sensitive, high-resolution detection of gene transcripts. Moreover, by employing multiple probes, this technique allows for multiplexed, simultaneous detection of distinct gene expression patterns spatiotemporally, making it a valuable spatial transcriptomics approach. Owing to these advantages, FISH techniques are rapidly being adopted across diverse areas of basic biology. However, conventional protocols often rely on volatile, toxic reagents such as formalin or methanol, posing potential health risks to researchers. Here, we present a safer protocol that replaces these chemicals with low-toxicity alternatives, without compromising the high detection sensitivity of FISH. We validated this protocol using both in situ hybridization chain reaction (HCR) and signal amplification by exchange reaction (SABER)-FISH in frozen sections of various model organisms, including mouse (Mus musculus), amphibians (Xenopus laevis and Pleurodeles waltl), and medaka (Oryzias latipes). Our results demonstrate successful multiplexed detection of morphogenetic and cell-type marker genes in these model animals using this safer protocol. The protocol has the additional advantage of requiring no proteolytic enzyme treatment, thus preserving tissue integrity. Furthermore, we show that this protocol is fully compatible with EGFP immunostaining, allowing for the simultaneous detection of mRNAs and reporter proteins in transgenic animals. This protocol retains the benefits of highly sensitive, multiplexed, and multimodal detection afforded by integrating in situ HCR and SABER-FISH with immunohistochemistry, while providing a safer option for researchers, thereby offering a valuable tool for basic biology.

Multiplexing samples in long-read sequencing with Oxford Nanopore Next Generation Sequencing Technology (ONT) by ligating specific native barcodes to individual DNA samples enables significant increases of high throughput sequencing combined with a significant reduction of sequencing costs. However, this advantage carries the risk of barcode misassignment / crosstalk. Employing ONT multiplex sequencing with samples, we observed misassigned barcodes so called barcode crosstalk, after ONT library preparation according to the standard protocol, particularly in samples with low input DNA concentrations. We assumed that these barcode misassignments are largely due to misligation of remaining native barcodes during subsequent the subsequent sequencing adapter ligation. To systematically investigate and quantify barcode crosstalk, genomic DNA (gDNA) from four bacterial type strains with different DNA input concentrations was prepared using three protocols for library preparation: the Nanopore standard protocol (protocol A: version valid until July 2, 2025) the new Nanopore protocol (protocol B: version from July 2, 2025), and an in house protocol with pooling of the barcoded samples only after the sequencing adapter ligation step (protocol C: in house). All samples were sequenced on a Nanopore PromethIon device. The results clearly showed that the use of protocol A resulted in a pronounced barcode crosstalk especially detectable in samples with low DNA input concentrations (up to 2.4% misassigned reads). The ONT adjustment in protocol B (altered washing buffer vs. protocol A) significantly alleviated the barcode crosstalk to below 0.01%, whereas protocol C eliminated barcode crosstalk virtually completely. These observations emphasize that sequencing results obtained with older ONT native barcoding protocol variants should be critically reviewed. The newer ONT barcoding protocol is preferable for sequencing, but it does not completely eliminate the barcode crosstalk effect. In conclusion, for low DNA input and high accuracy sequencing, protocol C is recommended.

Brain banks provide small tissue samples fixed in neutral-buffered-formalin (NBF), but human anatomy teaching laboratories could provide full brains fixed with solutions that are more appropriate for gross anatomy such as a saturated salt solution (SSS) or an alcohol-formaldehyde solution (AFS). Advanced aging and prolonged exposure to aldehydes are known to enhance brain tissue autofluorescence (AF), limiting the efficacy of immunofluorescence (IF) procedures. We have previously shown by IF staining the antigenicity preservation in mouse brains fixed with the three solutions. We now aimed to compare the quality of IF staining in human brains fixed with SSS, AFS and NBF. In addition, we compared the efficiency of AF quenching methods, namely the application of SudanBlackB (SBB) and the treatment of sections with sodium borohydride (NaBH4). Blocks of neocortex were extracted from 18 brains (NBF=6, SSS=6, AFS=6) and cut into 40{micro}m sections. Neurons (anti-NeuN, AlexaFluor-488) and astrocytes (anti-GFAP, AlexaFluor-555) were revealed with IF after an antigen retrieval protocol, while two treatments (SBB or NaBH4) were used to quench AF. We then assessed the degree of AF (criteria: background or cell AF) and the immunostaining quality with excitation wavelengths of 488nm, 555nm and 647nm. Brains fixed with all three solutions showed well-labeled astrocytes, whereas neurons werent always stained, but this was not associated to the fixative solution. The overall AF intensity was similar in sections from brains fixed with all three solutions. Finally, the SBB treatment was the most effective at reducing AF in all specimens. Given the similarity in AF and antigenicity assessment across the three solutions, we conclude that brains fixed with SSS and AFS could be good alternatives for NBF-fixed specimens in the context of IF experiments processed with a SBB protocol. Highlights- Immunofluorescence staining is feasible in brains fixed with anatomy labs solutions - GFAP is less affected by fixation than NeuN - Autofluorescence can be reduced by Sudan Black treatment

Winnie mice are a widely used in vivo model of inflammatory bowel disease carrying a missense mutation in the Muc2 gene. Here, we present a protocol for genotyping Winnie mice using TaqMan allelic discrimination quantitative PCR. We describe tissue collection, rapid crude DNA extraction, probe-based amplification with dual-labeled fluorophores, and fluorescence-based genotype calling in a single reaction. This protocol enables qualitative SNP genotyping without post-amplification processing and can be readily adapted to other defined point mutations. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=165 SRC="FIGDIR/small/704640v1_ufig1.gif" ALT="Figure 1"> View larger version (48K): org.highwire.dtl.DTLVardef@1f5d985org.highwire.dtl.DTLVardef@19bbd34org.highwire.dtl.DTLVardef@1a2d2fcorg.highwire.dtl.DTLVardef@c9baed_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LIAllelic discrimination qPCR protocol for genotyping the Muc2 p.Cys52Tyr mutation using dual-labeled hydrolysis probes C_LIO_LIEnables rapid discrimination of wild-type, heterozygous, and mutant alleles in a single reaction C_LIO_LICompatible with standard real-time PCR instruments and requires no post-PCR processing C_LIO_LISupports high-throughput genotyping from crude DNA with minimal hands-on time C_LI

Recent technological advances have made many "non-model" organisms accessible for experimental studies. However, reference inbred strains were not necessarily available, especially in marine invertebrates, and genetic background of organisms used for experiments are often non-uniform. This situation potentially affects experimental reproducibility. Although ascidians, Ciona intestinalis (type A, or C. robusta), are a widely used marine animal for many areas of experimental biology including developmental studies, no reference strains have been obtained despite extensive efforts. As an alternative way to improve reproducibility, we have established and maintained ascidian colonies through intra-population breeding every year from 2016 to 2020, and monitored genomic variants of these colonies. This method does not reduce genetic variations but instead manages and monitors genetic variations in the colonies, providing an easy and cost-effective way of increasing experimental reproducibility. Furthermore, we recently upgraded these genetically isolated, closed colonies that were re-established every year, and have maintained them for more than three years only through intra-population breeding and occasional back-cross using cryopreserved sperm. Genetic variants that we revealed using 3.7 tera-bases of sequence data will help to design future experiments in this species. Our data also show that two wild-populations, which were used to establish the colonies, have maintained distinct genetic backgrounds, although their habitats are directly linked to the Pacific Ocean and only 170 km apart. More importantly, genetic information regarding these colonies will undoubtedly improve experimental reproducibility and traceability, and our method will provide a realistic solution for performing reproducible experiments using non-model organisms.

Traditional nucleic acid extraction methods are costly, lengthy, and highly variable depending on the complexity of the sample matrix or the organism of interest. Workflows may exceed twenty steps, require separate kits for RNA and DNA, and demand expensive instrumentation, creating barriers to both speed and scalability. The AutolabTM HBH system addresses these limitations by using hyperbaric heating (HBH) to achieve temperatures above 100 {degrees}C in a sealed, pressurized environment through induction heating, enabling rapid lysis of diverse organisms and neutralization of macromolecular PCR inhibitors within minutes. The combination of extreme heat and HBH-optimized lyophilized reagents rapidly inactivates nucleases while preserving free nucleic acids. The workflow is streamlined to two steps: heating up to 1 mL of sample in the proprietary HBH bullet, followed by a brief centrifugation to pellet additives. The resulting supernatant is immediately compatible with real-time reverse transcription polymerase chain reaction (RT-PCR) and other downstream molecular assays. Here, we evaluate the systems broad compatibility with diverse sample buffers, matrices, and organisms. Comparative testing was conducted alongside Qiagen extraction methods to benchmark performance.

MOTIVATIONLongitudinal molecular studies of the mouse brain are limited by the need for terminal tissue collection. This prevents analysis of preexisting molecular states and their evolution within the same individual. We developed a stereotactic microbiopsy technique that enables minimally invasive sampling of defined brain regions in vivo. The method preserves survival while yielding material suitable for RNA and nuclei isolation. It provides a practical solution for linking baseline molecular states to subsequent behavioural, pharmacological, or disease-related outcomes. SUMMARYThis study presents a stereotactic microbiopsy technique for sampling defined brain regions in living mice, enabling transcriptomic and epigenomic analyses without sacrificing the animal. The method will allow pre-intervention tissue collection, making it possible to separate preexisting molecular differences from experience- or treatment-induced changes. We show that microbiopsies yield sufficient, high-quality RNA and chromatin for sequencing, with minimal tissue damage that largely resolves over time. The procedure uses standard stereotactic equipment and achieves reproducible spatial precision when the syringe is stabilised. This approach provides a practical framework for within-subject molecular comparisons, reducing animal use and enabling longitudinal profiling of the living mouse brain. It establishes a foundation for investigating how baseline molecular states influence later physiological or behavioural outcomes.

Fusion transcripts are composed of hybrid RNA consisting of transcripts from two distinct genes and can arise from physical linking of genes at the DNA level, splicing or read-through transcription. In addition, there are also fusion transcripts that can occur between a protein coding gene and long non-coding RNAs. Systemic detection of all fusion transcripts at the RNA-level is important in the identification of potential therapeutic drug targets as well as biomarkers for detection, classification, and subtyping of cancer. We used long-read third-generation sequencing of RNA, Iso Sequencing to identify fusion transcripts in Mantle Cell Lymphoma (MCL) cell lines. Our results revealed widespread transcript diversity in MCL. The majority of the long-read transcripts were novel. Some of the thousands of novel transcripts we identified were fusion transcripts. These fusion transcripts had some of the longest transcripts in the MCL transcriptome. We identified the fusion junction of several select fusion transcripts involving protein coding genes including the well-known and widely expressed CTBS::GNG5 and validated their presence using other techniques. Furthermore, we also identified and validated a novel fusion transcript between the multifunctional, m6A methylation writer, RBM15, and LAMTOR5:AS, a long noncoding RNA. Use of the chemical compound, JT-607, an inhibitor of CPSF73/CPSF3 which affects both alternative polyadenylation and read-through transcription resulted in increased expression of the RBM15::LAMTOR5:AS fusion transcript. Our analysis suggests that RBM15::LAMTOR5:AS and many fusion transcripts we identified are intrachromosomal. Since the origin, significance and impact of many fusion transcripts remain unknown, our results support using an unbiased approach to identify fusion transcripts. This will help us to fully comprehend the complexity of the human transcriptome in normal biology and in disease.

The oral microbiome is a complex community of bacteria, fungi, and viruses that inhabit the oral cavity. Microbes of the oral microbiome are implicated in health and disease. We collected 220 unstimulated saliva samples from patients with periodontal disease and varying degrees of dental caries, as well as from subjects with no signs of oral disease. Metagenomic analysis of saliva revealed significantly higher abundance of periodontal pathogens in people with gum disease, and significantly higher abundance of cariogenic species in people with dental caries. We also found that salivary microbiome diversity was significantly higher in people with periodontal disease, but not in those with only caries. Furthermore, oral microbiome diversity is affected by oral hygiene habits such as flossing frequency, but not brushing frequency. Clustering and differential analysis allowed us to identify specific commensal species, such as Prevotella pallens and Veillonella atypica, which are significantly higher in patients without oral disease. Clustering further suggested that oral microbiome diversity may contribute to disease risk. These results suggest that oral hygiene behaviors influence the oral microbiome, and modulation of the oral microbiome could prevent or reduce the incidence and severity of oral disease.

Accurate quantification of fungi is important for a myriad of applications but remains challenging. Previously, we demonstrated that an approach called the adenine-HPLC method can quantify bacteria, including those with aggregating properties that are difficult to quantify using conventional methods, by measuring cellular adenine derived from DNA and converting the adenine amount to genome copy number, without being influenced by cell morphology. However, in this study, when this adenine-HPLC method was applied to the quantification of budding yeast as a model fungus, accurate measurement proved impossible. This limitation was attributed to adenine release from other adenine-containing biomolecules, such as RNA and ATP, and we therefore developed a method that suppresses adenine release from these molecules. This method involves reducing the temperature of the acid treatment and prewashing the cells before acid treatment. In addition, we incorporated a process that corrects for the naturally occurring free adenine level as background during total adenine measurement. The improved adenine-HPLC method based on these modifications enables accurate quantification of budding yeast using genomic DNA content in whole cells as the quantification unit.

The expansion of short tandem repeats is a feature of over 60 different human diseases. Ongoing somatic instability throughout a patients lifetime can influence disease progression and has emerged as a therapeutic target. Understanding its mechanism is essential for the identification of both drug targets and therapeutic interventions. A major obstacle towards this translational goal has been to measure changes in repeat size distribution in a timely manner. To address this, here we present Single Clone-based Instability Assay (SCIA), a streamlined experimental design that saves weeks in assessing the effect of a gene knockout on repeat instability. The approach avoids bulk cultures and does not require a reporter cell line. It uses targeted long-read sequencing as a readout for repeat instability. We have validated the approach using FAN1, PMS1, and MLH1 knockouts in HEK293-derived cells. We provide a visualization software that generates delta plots, extracts the instability frequency, the bias towards expansion or contraction, and the average size of the changes. Using SCIA, we find that although FAN1 knockout clones showed increased frequency of expansions, the size of the expansions were smaller. This highlights the wealth of information that can be extracted and the potential for novel insights into the mechanism of repeat instability.

ObjectiveThis study utilizes small-sample periodontitis data to exploratively investigate causal relationships between the oral microbiome and periodontitis in East Asian populations. We aimed to identify specific oral microbial taxa that may drive disease pathogenesis. Given the exploratory nature of the dataset, findings should be interpreted as hypothesis-generating. MethodsWe performed a two-sample Mendelian randomization (MR) analysis using genome-wide association study (GWAS) summary statistics for tongue dorsum and salivary microbiomes alongside periodontitis data in East Asian populations. Primary causal estimates were derived using the inverse-variance weighted (IVW) method, supplemented by MR-Egger, weighted median, weighted mode, and simple mode methods. To ensure robustness, we assessed heterogeneity using Cochrans Q test, evaluated horizontal pleiotropy via the MR-Egger intercept and MR-PRESSO tests, and applied Steiger filtering to rule out reverse causality. ResultsWe identified 60 species-level microbial taxa causally associated with periodontitis, comprising 29 negative and 31 positive associations. These taxa were predominantly enriched within the genera Campylobacter, Pauljensenia, Solobacterium, and Streptococcus. ConclusionThis study provides tentative evidence for causal links between specific species-level oral microbial taxa and periodontitis, highlighting potential targets for prevention and therapeutic intervention.

ObjectiveGeneration and testing of IGF1 reference materials (RM), suitable for the harmonization of immunoassay (IA) and LC-MS/MS methods for the IGF1 determination in blood. In addition, establishment of age related reference intervals for men and women. MethodsIn a split sample study of 42 patients, and 30 healthy volunteers we tested the commutability of four RMs for IGF1, using four commercial IAs and an LC-MS/MS method. A new set of age dependent reference intervals was established using Lifelines biobank samples, based on the IGF1 LC-MS/MS method. ResultsThe four RMs were found to be commutable, except the RM with the lowest concentration measured with the Siemens Immulite method. The value assignment of the RMs was based on the IGF1 LC-MS/MS method, which was calibrated against WHO international standard 02/254. LC-MS/MS results were on average about 0 to 60% lower than those of the immunoassays. Combining the recalculated IGF1 results in patient samples from a former study with the data from healthy volunteers in this study, showed a reduction in the variation of the data points (standard error of estimate) of 42% and 62% respectively. ConclusionCommutable RMs for IGF1 can be made from serum of healthy blood donors. However, it remains necessary to test the commutability of these RMs in IAs that were not included in this study. By harmonizing methods using the four RMs, the same age-related reference intervals can be used.

BackgroundConventional clinical indicators of periodontitis progression detect disease after irreversible tissue destruction has occurred. Molecular biomarkers in gingival crevicular fluid (GCF) offer potential for earlier detection, but existing analytical approaches rely on cross-sectional snapshots that fail to capture the temporal dynamics of disease evolution. AimTo develop and validate a temporal deep learning framework leveraging longitudinal GCF protein profiles for (1) regression-based prediction of clinical attachment level (CAL) and probing depth (PD) changes, (2) current-visit classification of periodontitis progression, (3) next-visit prediction of progression with a 2-month clinical lead time, and (4) identification of the most informative biomarkers through systematic multi-method feature importance analysis. Materials and MethodsThis study utilized longitudinal GCF data from a prospective cohort of 413 participants (501 periodontal sites, 3,792 time-series observations) with 64 protein biomarkers measured at 2-month intervals over 12 months. A compact encoder-gated recurrent unit (GRU)-decoder architecture was developed through systematic experimentation across four phases, benchmarking temporal deep learning against cross-sectional machine learning baselines. Task-specific decoders addressed continuous regression (CAL and PD prediction) and binary classification (progression detection). Model development and reporting followed the TRIPOD+AI guidelines. ResultsThe temporal GRU achieved 47.7% CAL mean absolute error (MAE) reduction (1.139 to 0.596 mm) and 41.0% PD MAE reduction (0.902 to 0.532 mm) over linear regression baselines through the systematic model development progression. For binary classification, the model achieved AUC-ROC of 0.886 for current-visit classification and 0.867 for next-visit prediction with a 2-month lead time. Per-visit analysis revealed progressive improvement in both regression and classification accuracy as longitudinal data accumulated. Cross-method feature importance analysis identified Periostin, VEGF, MMP-2, IL-1RA, and MCP-4 as core predictive biomarkers, with divergent profiles between diagnostic and prognostic tasks suggesting distinct molecular signatures for concurrent versus incipient progression. ConclusionsTemporal deep learning applied to longitudinal GCF protein profiles enables both accurate regression prediction of clinical parameters and reliable classification of progression status, including 2-month-ahead forecasting suitable for clinical intervention planning. The compact architecture and non-invasive sampling approach make this framework suitable for integration into point-of-care periodontal monitoring workflows. Clinical RelevanceConventional clinical indicators of periodontitis progression, including probing depth changes, attachment loss, and radiographic bone loss, inherently detect disease after irreversible damage has occurred. This study shows that a compact deep learning model analyzing temporal GCF protein profiles can first accurately predict continuous changes in pocket depth and attachment loss, then classify progression status 2 months in advance, enabling proactive intervention before clinical manifestation of tissue destruction.

Accurate detection of RNA splice variants is often hindered when transcripts lack large distinguishable exonic regions, making conventional PCR strategies challenging. We developed a simple melting temperature (Tm)-guided exon-exon junction (EEJ) RT-PCR method to enable variant-specific detection under these conditions. Uni-directional primers spanning exon-exon junctions were designed so that approximately each half anneals to adjacent exons. The Tm of each half-site was set >7{degrees}C below the annealing temperature, preventing stable binding to individual exons and enforcing junction-dependent amplification. The method was evaluated using HTRA1-AS1 long noncoding RNA variants that share overlapping exon sequences but differ in splice connectivity. HTRA1-AS1 comprises five variants, only one with a large distinguishable exon. Tm-guided EEJ primers robustly discriminated the remaining four variants. After optimization, amplification yielded sharp, single bands with minimal cross-reactivity. Compared with conventional designs, this approach reduced heteroduplex and heteroquadruplex formation, improving band clarity. Sanger sequencing confirmed junction specificity, and the method performed well in multiplex settings. Overall, Tm-guided EEJ RT-PCR is a cost-effective, high-resolution approach for detecting RNA variants lacking easily distinguishable exonic regions, readily compatible with standard RT-PCR and qPCR workflows.

The purpose of this study was to evaluate the use of carrier DNA (i.e., exogenous DNA spike-in) for shotgun metagenome sequencing of ultra-low levels (less than 50 picograms) of metagenomic DNA. We hypothesized that carrier DNA would improve the robustness of library preparation for samples with DNA concentrations below detection by providing a tangible amount of known DNA thereby bringing total DNA concentrations closer to recommended input ranges for metagenomic library kits. We employed adaptive PCR cycling using an iconPCR instrument (N6tec) to allow dynamic thermocycling until sufficient library for sequencing was amplified, regardless of input DNA concentration. Libraries were sequenced and mapped to reference genomes of lambda and mock community organisms, and outcome measures included total reads, on-target reads, evenness of coverage across 10 organisms within each mock community, and PCR duplication rate. We demonstrate that libraries can be prepared down to 50 femtograms of input DNA, but that there is a strong correlation between input DNA concentration and PCR duplication rate. The utility of spiking in carrier DNA is equivocal as it mildly negatively impacts the observed distribution of mock communities and serves as a loss of sequencing output. Although the loss of sequencing capacity due to carrier DNA can be partially offset by reduced loss of data from PCR duplication, carrier DNA spike-in is not recommended for routine library preparation of ultra-low input samples. Adaptive cycling allows for appropriate cycling conditions when input DNA concentrations are below detection.

Here we evaluated the performance of a previously published tiling PCR primer scheme by Ringlander et al. (2022) for whole-genome amplification of Hepatitis B virus (HBV) in combination with Oxford Nanopore sequencing. The primer set originally developed for Ion Torrent sequencing was adapted by removing platform-specific adapters and tested using clinical serum or plasma samples submitted for routine HBV genotyping and resistance testing. Two multiplexing strategies were compared: a single PCR pool containing all primers and a two-pool strategy with non-overlapping amplicons. Sequencing reads were processed using a Nanopore analysis pipeline, and genome coverage and amplicon performance were compared across samples spanning a wide Ct range and representing HBV genotypes A-E. Across all samples, the median genome coverage was approximately 50%, although recovery varied widely, ranging from complete failure to nearly full genomes. Combining all primers into a single PCR reaction, or separating overlapping amplicons into different reactions, had little overall impact on genome recovery, and no consistent differences between the two pooling strategies were observed. In contrast, amplification efficiency differed markedly between individual amplicons. Amplicons 1-5 generally produced higher sequencing depth, whereas amplicons 6-10 frequently showed low coverage and contributed to incomplete genome recovery. Genome coverage was strongly associated with Ct values, with higher coverage observed in samples with lower Ct values, while coverage was broadly similar across genotypes. These results demonstrate that the Ringlander et al. primer scheme can be adapted for multiplex PCR and Nanopore sequencing of HBV, but uneven amplicon performance limits consistent full-genome recovery and highlights the need for further optimization of HBV tiling PCR designs.