An Introduction to Rbowtie2

In Rbowtie2: An R Wrapper for Bowtie2 and AdapterRemoval

knitr::opts_chunk$set(echo = TRUE)

Introduction

The package provides an R wrapper of Bowtie2 and AdapterRemoval. Bowtie2 is the popular sequencing reads aligner, which is good at aligning reads with length above 50bp[1]. AdapterRemoval is a convenient tool for rapid adapter trimming, identification, and read merging[2]. Both of them are implemented with C++. We wrap them into an R package that provide user friendly interfaces for R users.

You can preprocess the raw sequencing data by using AadapterRemoval even if adapter(s) information is missing. Then, Bowtie2 can aligned these preprocessed reads to the references.

This package is developed and maintained by members of Xiaowo Wang Lab

MOE Key Laboratory of Bioinformatics and Bioinformatics Division,

TNLIST / Department of Automation, Tsinghua University

contact:{wei-z14,w-zhang16}(at)mails.tsinghua.edu.cn

An Example Workflow by Using Rbowtie2

Installation

To install the latest version of Rbowtie2, you will need to be using the latest version of R. Rbowtie2 is part of Bioconductor project, so you can install Rbowtie2 and its dependencies like this:

if (!requireNamespace("BiocManager", quietly=TRUE))
    install.packages("BiocManager")
BiocManager::install("Rbowtie2")

Loading

Just like other R package, you need to load Rbowtie2 like this each time before using the package.

library(Rbowtie2)

AdapterRemoval

All package functions mentioned in this subsection use the binary of AdapterRemoval.

Idetitify Adapter

If you know the adapter sequence of reads files, you can skip this step. Besides,single end data is not support for this function yet so adapter sequence has to be known .

reads_1 and reads_2 are raw paired-end reads file with fastq format. adapters is two adapters character vector.

td <- tempdir()
reads_1 <- system.file(package="Rbowtie2", "extdata", "adrm", "reads_1.fq")
reads_2 <- system.file(package="Rbowtie2", "extdata", "adrm", "reads_2.fq")
(adapters <- 
    identify_adapters(file1=reads_1,file2=reads_2,
                      basename=file.path(td,"reads"),
                      "--threads 3",overwrite=TRUE))

Remove Adapter

With known adapter sequence, remove_adapter function can be call to trim adapters.

(cmdout<-remove_adapters(file1=reads_1,file2=reads_2,adapter1 = adapters[1], 
                adapter2 = adapters[2],
output1=file.path(td,"reads_1.trimmed.fq"),
output2=file.path(td,"reads_2.trimmed.fq"),
basename=file.path(td,"reads.base"),overwrite=TRUE,"--threads 3"))

Additional Arguments and Version

If you need to set additional arguments like "--threads 3" above, you can call function below to print all options available. The fixed arguments like file1, file2 and basename etc. are invalid.

adapterremoval_usage()

You can get version information by call:

adapterremoval_version()

Bowtie2

All package functions mentioned in this subsection use the binary of Bowtie2. Note that Bowtie2 is support 64bit R.

Build Bowtie2 Index

Before aligning reads, bowtie2 index should be build. refs is a character vector of fasta reference file paths. A prefix of bowtie index should be set to argument bt2Index. Then, 6 index files with .bt2 file name extension will be created with bt2Index prefix.

td <- tempdir()
refs <- dir(system.file(package="Rbowtie2", "extdata", "bt2","refs"),full=TRUE)
(cmdout<-bowtie2_build(references=refs, 
              bt2Index=file.path(td, "lambda_virus"), "--threads 4 --quiet",
              overwrite=TRUE))

Additional Arguments of Bowtie Build

If you need to set additional arguments like "--threads 4 --quiet" above, you can call function below to print all options available. The fixed arguments references, bt2Index are invalid.

bowtie2_build_usage()

Bowtie2 Alignment

The variable reads_1 and reads_1 are preprocessed reads file paths. With bowtie2 index, reads will be mapped to reference by calling bowtie2. The result is saved in a sam file whose path is set to samOutput

reads_1 <- system.file(package="Rbowtie2", "extdata", 
                       "bt2", "reads", "reads_1.fastq")
reads_2 <- system.file(package="Rbowtie2", "extdata", 
                       "bt2", "reads", "reads_2.fastq")
if(file.exists(file.path(td, "lambda_virus.1.bt2"))){
    (cmdout<-bowtie2(bt2Index = file.path(td, "lambda_virus"),
        samOutput = file.path(td, "result.sam"),
    seq1=reads_1,seq2=reads_2,overwrite=TRUE,"--threads 3"))
    head(readLines(file.path(td, "result.sam")))
}

Additional Arguments and Version of Bowtie2 Aligner

If you need to set additional arguments like "--threads 3" above, you can call function below to print all options available. The fixed arguments like bt2Index, samOutput and seq1 etc. are invalid.

bowtie2_usage()

You can get version information by call:

bowtie2_version()

Session Infomation

sessionInfo()

Acknowledgement

We would like to thank Huan Fang for package testing and valuable suggestions.

References

[1] Langmead, B., & Salzberg, S. L. (2012). Fast gapped-read alignment with Bowtie 2. Nature methods, 9(4), 357-359.

[2] Schubert, Lindgreen, and Orlando (2016). AdapterRemoval v2: rapid adapter trimming, identification, and read merging. BMC Research Notes, 12;9(1):88.

Rbowtie2 documentation built on Nov. 8, 2020, 5:35 p.m.