UNCROSS: Filtering of high-frequency cross-talk in 16S amplicon reads

Next-generation amplicon sequencing is widely used for surveying biological diversity in applications such as microbial metagenomics, immune system repertoire analysis and targeted tumor sequencing of cancer-associated genes. In such studies, assignment of reads to incorrect samples (cross-talk) is a well-documented problem that is rarely considered in practice. By considering unexpected OTUs in artificial (mock) samples, I estimate that cross-talk occurred for ~2% of the reads in one Illumina GAIIx run and eleven Illumina MiSeq runs targeting 16S ribosomal RNA. I also describe UNCROSS, an algorithm for detecting and filtering cross-talk in OTU tables.

De NovoAssembly of the Pea (Pisum sativumL.) Nodule Transcriptome

The large size and complexity of the garden pea (Pisum sativumL.) genome hamper its sequencing and the discovery of pea gene resources. Although transcriptome sequencing provides extensive information about expressed genes, some tissue-specific transcripts can only be identified from particular organs under appropriate conditions. In this study, we performed RNA sequencing of polyadenylated transcripts from young pea nodules and root tips on an Illumina GAIIx system, followed byde novotranscriptome assembly using the Trinity program. We obtained more than 58,000 and 37,000 contigs from “Nodules” and “Root Tips” assemblies, respectively. The quality of the assemblies was assessed by comparison with pea expressed sequence tags and transcriptome sequencing project data available from NCBI website. The “Nodules” assembly was compared with the “Root Tips” assembly and with pea transcriptome sequencing data from projects indicating tissue specificity. As a result, approximately 13,000 nodule-specific contigs were found and annotated by alignment to known plant protein-coding sequences and by Gene Ontology searching. Of these, 581 sequences were found to possess full CDSs and could thus be considered as novel nodule-specific transcripts of pea. The information about pea nodule-specific gene sequences can be applied for gene-based markers creation, polymorphism studies, and real-time PCR.

Analysis of the Mitochondrial Genome of a Novosvobodnaya Culture Representative using Next-Generation Sequencing and Its Relation to the Funnel Beaker Culture

The Novosvobodnaya culture is known as a Bronze Age archaeological culture in the North Caucasus region of Southern Russia. It dates back to the middle of the 4th millennium B.C. and seems to have occurred during the time of the Maikop culture. There are now two hypotheses about the emergence of the Novosvobodnaya culture. One hypothesis suggests that the Novosvobodnaya culture was a phase of the Maikop culture, whereas the other one classifies it as an independent event based on the material culture items found in graves. Comparison between Novosvobodnaya pottery and Funnelbeaker (TRB) pottery from Germany has allowed researchers to suggest that the Novosvobodnaya culture developed under the influence of Indo-European culture. Nevertheless, the origin of the Novosvobodnaya culture remains a matter of debate. We applied next-generation sequencing to study ~5000-year-old human remains from the Klady kurgan grave in Novosvobodnaya stanitsa (now the Republic of Adygea, Russia). A total of 58,771,105 reads were generated using Illumina GAIIx with a coverage depth of 13.4х over the mitochondrial (mt) DNA genome. The mtDNA haplogroup affiliation was determined as V7, suggesting a role of the TRB culture in the development of the Novosvobodnaya culture and supporting the model of sharing between Novosvobodnaya and early Indo-European cultures.