Influence of 16S rDNA primer sequence mismatches on the spectrum of bacterial genera detected in prostate tissue by universal eubacterial PCR

Identification of human gene research articles with wrongly identified nucleotide sequences

Nucleotide sequence reagents underpin molecular techniques that have been applied across hundreds of thousands of publications. We have previously reported wrongly identified nucleotide sequence reagents in human research publications and described a semi-automated screening tool Seek & Blastn to fact-check their claimed status. We applied Seek & Blastn to screen >11,700 publications across five literature corpora, including all original publications in Gene from 2007 to 2018 and all original open-access publications in Oncology Reports from 2014 to 2018. After manually checking Seek & Blastn outputs for >3,400 human research articles, we identified 712 articles across 78 journals that described at least one wrongly identified nucleotide sequence. Verifying the claimed identities of >13,700 sequences highlighted 1,535 wrongly identified sequences, most of which were claimed targeting reagents for the analysis of 365 human protein-coding genes and 120 non-coding RNAs. The 712 problematic articles have received >17,000 citations, including citations by human clinical trials. Given our estimate that approximately one-quarter of problematic articles may misinform the future development of human therapies, urgent measures are required to address unreliable gene research articles.

The thin ret(raction) line: biomedical journal responses to incorrect non-targeting nucleotide sequence reagents in human gene knockdown publications

The capacity of the scientific literature to self-correct is of vital importance, but few studies have compared post-publication journal responses to specific error types. We have compared journal responses to a specific reagent error in 31 human gene knockdown publications, namely a non-targeting or negative control nucleotide sequence that is instead predicted to target a human gene. The 31 papers published by 13 biomedical journals generated 26 published responses (14 retractions, 5 expressions of concern, 7 author corrections which included one resolved expression of concern) as well as 6 stated decisions to take no action. Variations in published responses were noted both between journals and by 4 journals that published different responses to at least 2 papers. A subset of published responses revealed conflicting explanations for the wrongly identified control reagent, despite 30/31 papers obtaining their gene knockdown reagents from the same external supplier. Viewed collectively, different journal responses to human gene knockdown publications with a common reagent error type suggest that editorial staff require more support to interpret post-publication notifications of incorrect nucleotide sequence reagents. We propose a draft template to facilitate the communication, interpretation and investigation of published errors, including errors affecting research reagents.

CoMA - an intuitive and user-friendly pipeline for amplicon-sequencing data analysis

In recent years, there has been a veritable boost in next-generation sequencing (NGS) of gene amplicons in biological and medical studies. Huge amounts of data are produced and need to be analyzed adequately. Various online and offline analysis tools are available; however, most of them require extensive expertise in computer science or bioinformatics, and often a Linux-based operating system. Here, we introduce "CoMA-Comparative Microbiome Analysis" as a free and intuitive analysis pipeline for amplicon-sequencing data, compatible with any common operating system. Moreover, the tool offers various useful services including data pre-processing, quality checking, clustering to operational taxonomic units (OTUs), taxonomic assignment, data post-processing, data visualization, and statistical appraisal. The workflow results in highly esthetic and publication-ready graphics, as well as output files in standardized formats (e.g. tab-delimited OTU-table, BIOM, NEWICK tree) that can be used for more sophisticated analyses. The CoMA output was validated by a benchmark test, using three mock communities with different sample characteristics (primer set, amplicon length, diversity). The performance was compared with that of Mothur, QIIME and QIIME2-DADA2, popular packages for NGS data analysis. Furthermore, the functionality of CoMA is demonstrated on a practical example, investigating microbial communities from three different soils (grassland, forest, swamp). All tools performed well in the benchmark test and were able to reveal the majority of all genera in the mock communities. Also for the soil samples, the results of CoMA were congruent to those of the other pipelines, in particular when looking at the key microbial players.

Characterisation of microbial communities within aggressive prostate cancer tissues

Background

An infectious aetiology for prostate cancer has been conjectured for decades but the evidence gained from questionnaire-based and sero-epidemiological studies is weak and inconsistent, and a causal association with any infectious agent is not established. We describe and evaluate the application of new technology to detect bacterial and viral agents in high-grade prostate cancer tissues. The potential of targeted 16S rRNA gene sequencing and total RNA sequencing was evaluated in terms of its utility to characterise microbial communities within high-grade prostate tumours.

Methods

Two different Massively Parallel Sequencing (MPS) approaches were applied. First, to capture and enrich for possible bacterial species, targeted-MPS of the V2-V3 hypervariable regions of the 16S rRNA gene was performed on DNA extracted from 20 snap-frozen prostate tissue cores from ten “aggressive” prostate cancer cases. Second, total RNA extracted from the same prostate tissue samples was also sequenced to capture the sequence profile of both bacterial and viral transcripts present.

Results

Overall, 16S rRNA sequencing identified Enterobacteriaceae species common to all samples and P. acnes in 95% of analyzed samples. Total RNA sequencing detected endogenous retroviruses providing proof of concept but there was no evidence of bacterial or viral transcripts suggesting active infection, although it does not rule out a previous ‘hit and run’ scenario.

Conclusions

As these new investigative methods and protocols become more refined, MPS approaches may be found to have significant utility in identifying potential pathogens involved in disease aetiology. Further studies, specifically designed to detect associations between the disease phenotype and aetiological agents, are required.

Electronic supplementary material

The online version of this article (doi:10.1186/s13027-016-0112-7) contains supplementary material, which is available to authorized users.

Effect of hypertension on bacteria composition of prostate biopsy in patients with benign prostatic hyperplasia and prostate cancer in PSA grey-zone

Diagnostic prostate cancer (PC) is difficult to diagnose by prostate biopsy, even in patients with markedly elevated PSA levels. Therefore, we aimed to identify a new, better technique to detect PC in a more consistent manner. A variety of steps were employed to validate this proposed method, including DNA extraction, polymerase chain reaction (PCR) amplification, denaturing gradient gel electrophoresis (DGGE) and DGGE band sequencing. Four transperineal prostate biopsy specimens were obtained from male patients. The patients were under the age of 65 and PSA levels were 4-10 ng/ml. We also investigated the bacteria composition of transperineal prostate biopsy in patients with benign prostatic hyperplasia (BPH) and PC by PCR-DGGE profiling. Sequences from selected bands 2 and 4 both matched with Sphingomonas, which is present in lower amounts in PC without hypertension as compared to PC with hypertension, while there were no particular differences in the BPH group. Specific bacteria from the prostate biopsy tissues provide further confidence in PC diagnosis based on a PCR approach as a diagnostic tool, while hypertension was found to be a disturbing factor that can affect the diagnosis of BPH and PC in grey-zone.

Multi-template polymerase chain reaction

PCR is a formidable and potent technology that serves as an indispensable tool in a wide range of biological disciplines. However, due to the ease of use and often lack of rigorous standards many PCR applications can lead to highly variable, inaccurate, and ultimately meaningless results. Thus, rigorous method validation must precede its broad adoption to any new application. Multi-template samples possess particular features, which make their PCR analysis prone to artifacts and biases: multiple homologous templates present in copy numbers that vary within several orders of magnitude. Such conditions are a breeding ground for chimeras and heteroduplexes. Differences in template amplification efficiencies and template competition for reaction compounds undermine correct preservation of the original template ratio. In addition, the presence of inhibitors aggravates all of the above-mentioned problems. Inhibitors might also have ambivalent effects on the different templates within the same sample. Yet, no standard approaches exist for monitoring inhibitory effects in multitemplate PCR, which is crucial for establishing compatibility between samples.

External and semi-internal controls for PCR amplification of homologous sequences in mixed templates

In a mixed template, the presence of homologous target DNA sequences creates environments that almost inevitably give rise to artifacts and biases during PCR. Heteroduplexes, chimeras, and skewed template-to-product ratios are the exclusive attributes of mixed template PCR and never occur in a single template assay. Yet, multi-template PCR has been used without appropriate attention to quality control and assay validation, in spite of the fact that such practice diminishes the reliability of results. External and internal amplification controls became obligatory elements of good laboratory practice in different PCR assays. We propose the inclusion of an analogous approach as a quality control system for multi-template PCR applications. The amplification controls must take into account the characteristics of multi-template PCR and be able to effectively monitor particular assay performance. This study demonstrated the efficiency of a model mixed template as an adequate external amplification control for a particular PCR application. The conditions of multi-template PCR do not allow implementation of a classic internal control; therefore we developed a convenient semi-internal control as an acceptable alternative. In order to evaluate the effects of inhibitors, a model multi-template mix was amplified in a mixture with DNAse-treated sample. Semi-internal control allowed establishment of intervals for robust PCR performance for different samples, thus enabling correct comparison of the samples. The complexity of the external and semi-internal amplification controls must be comparable with the assumed complexity of the samples. We also emphasize that amplification controls should be applied in multi-template PCR regardless of the post-assay method used to analyze products.