Contents

1 About metabinR

The goal of metabinR is to provide functions for performing abundance and composition based binning on metagenomic samples, directly from FASTA or FASTQ files.

Abundance based binning is performed by analyzing sequences with long kmers (k>8), whereas composition based binning is performed by utilizing short kmers (k<8).

2 Installation

To install metabinR package:

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

3 Preparation

3.1 Allocate RAM and load required libraries

In order to allocate RAM, a special parameter needs to be passed while JVM initializes. JVM parameters can be passed by setting java.parameters option. The -Xmx parameter, followed (without space) by an integer value and a letter, is used to tell JVM what is the maximum amount of heap RAM that it can use. The letter in the parameter (uppercase or lowercase), indicates RAM units. For example, parameters -Xmx1024m or -Xmx1024M or -Xmx1g or -Xmx1G, all allocate 1 Gigabyte or 1024 Megabytes of maximum RAM for JVM.

options(java.parameters="-Xmx1500M")
unloadNamespace("metabinR")
library(metabinR)
library(data.table)
library(dplyr)
library(ggplot2)
library(gridExtra)
library(cvms)
library(sabre)

4 Abundance based binning example

In this example we use the simulated metagenome sample (see sample data) to perform abundance based binning. The simulated metagenome contains 26664 Illumina reads (13332 pairs of 2x150bp) that have been sampled from 10 bacterial genomes in such a way (log-norm abundances) that each read is belongs to one of two abundance classes (class 1 of high abundant taxa and class 2 of low abundant taxa).

We first get the abundance information for the simulated metagenome :

abundances <- read.table(
    system.file("extdata", "distribution_0.txt",package = "metabinR"),
    col.names = c("genome_id", "abundance" ,"AB_id"))

In abundances data.frame, column genome_id is the bacterial genome id, column abundance is the abundance ratio and column AB_id is the original abundance class (in this example 1 or 2).

Then we get the read mapping information (from which bacterial genome each read is originating from and in which abundance class belongs) :

reads.mapping <- fread(system.file("extdata", "reads_mapping.tsv.gz",
                                   package = "metabinR")) %>%
    merge(abundances[, c("genome_id","AB_id")], by = "genome_id") %>%
    arrange(anonymous_read_id)

In reads.mapping data.frame, column anonymous_read_id is the read id, column genome_id is the original bacterial genome id and column AB_id is the original abundance class id.

We perform Abundance based Binning on the simulated reads, for 2 abundance classes and analyzing data with 10-mers. The call returns a dataframe of the assigned abundance cluster and distances to all clusters for each read :

assignments.AB <- abundance_based_binning(
        system.file("extdata","reads.metagenome.fasta.gz", package="metabinR"),
        numOfClustersAB = 2, 
        kMerSizeAB = 10, 
        dryRun = FALSE, 
        outputAB = "vignette") %>%
    arrange(read_id)

Note that read id of fasta header matches anonymous_read_id of reads.mapping.

Call to will produce 2 fasta file, one for each of the abundance classes, containing fasta reads assigned to each class. It will also produce a file containing histogram information of kmers counted. We can plot this histogram as :

histogram.AB <- read.table("vignette__AB.histogram.tsv", header = TRUE)
ggplot(histogram.AB, aes(x=counts, y=frequency)) + 
    geom_area() +
    labs(title = "kmer counts histogram") + 
    theme_bw()

We get the assigned abundance class for each read in assignments.AB$AB

Then we evaluate predicted abundance class and plot confusion matrix :

eval.AB.cvms <- cvms::evaluate(data = data.frame(
                                    prediction=as.character(assignments.AB$AB),
                                    target=as.character(reads.mapping$AB_id),
                                    stringsAsFactors = FALSE),
                                target_col = "target",
                                prediction_cols = "prediction",
                                type = "binomial"
)
eval.AB.sabre <- sabre::vmeasure(as.character(assignments.AB$AB),
                                as.character(reads.mapping$AB_id))

p <- cvms::plot_confusion_matrix(eval.AB.cvms) +
        labs(title = "Confusion Matrix", 
                x = "Target Abundance Class", 
                y = "Predicted Abundance Class")
tab <- as.data.frame(
    c(
        Accuracy =  round(eval.AB.cvms$Accuracy,4),
        Specificity =  round(eval.AB.cvms$Specificity,4),
        Sensitivity =  round(eval.AB.cvms$Sensitivity,4),
        Fscore =  round(eval.AB.cvms$F1,4),
        Kappa =  round(eval.AB.cvms$Kappa,4),
        Vmeasure = round(eval.AB.sabre$v_measure,4)
    )
)
grid.arrange(p, ncol = 1)

knitr::kable(tab, caption = "AB binning evaluation", col.names = NULL)

Table 1: AB binning evaluation
Accuracy 0.8700
Specificity 0.9058
Sensitivity 0.7608
Fscore 0.7430
Kappa 0.6560
Vmeasure 0.3553

5 Composition based binning example

In a similar way, we analyze the simulated metagenome sample with the Composition based Binning module.

The simulated metagenome contains 26664 Illumina reads (13332 pairs of 2x150bp) that have been sampled from 10 bacterial genomes. The originating bacteria genome is therefore the true class information of each read in this example.

We first get the read mapping information (from which bacterial genome each read is originating from) :

reads.mapping <- fread(
        system.file("extdata", "reads_mapping.tsv.gz",package = "metabinR")) %>%
    arrange(anonymous_read_id)

In reads.mapping data.frame, column anonymous_read_id is the read id and column genome_id is the original bacterial genome id.

We perform Composition based Binning on the simulated reads, for 10 composition classes (one for each bacterial genome) and analyzing data with 6-mers. The call returns a dataframe of the assigned composition cluster and distances to all clusters for each read :

assignments.CB <- composition_based_binning(
        system.file("extdata","reads.metagenome.fasta.gz",package ="metabinR"),
        numOfClustersCB = 10, 
        kMerSizeCB = 4, 
        dryRun = TRUE, 
        outputCB = "vignette") %>%
    arrange(read_id)

Note that read id of fasta header matches anonymous_read_id of reads.mapping.

Since this is a clustering problem, it only makes sense to calculate Vmeasure and other an extrinsic measures like Homogeneity and completeness.

eval.CB.sabre <- sabre::vmeasure(as.character(assignments.CB$CB),
                                as.character(reads.mapping$genome_id))
tab <- as.data.frame(
    c(
        Vmeasure = round(eval.AB.sabre$v_measure,4),
        Homogeneity = round(eval.AB.sabre$homogeneity,4),
        Completeness = round(eval.AB.sabre$completeness,4)
    )
)
knitr::kable(tab, caption = "CB binning evaluation", col.names = NULL)

Table 2: CB binning evaluation
Vmeasure 0.3553
Homogeneity 0.3514
Completeness 0.3594

6 Hierarchical (2step ABxCB) binning example

Finally, we analyze the simulated metagenome sample with the Hierarchical Binning module.

The simulated metagenome contains 26664 Illumina reads (13332 pairs of 2x150bp) that have been sampled from 10 bacterial genomes. The originating bacteria genome is therefore the true class information of each read in this example.

We first get the read mapping information (from which bacterial genome each read is originating from) :

reads.mapping <- fread(
        system.file("extdata", "reads_mapping.tsv.gz",package = "metabinR")) %>%
    arrange(anonymous_read_id)

In reads.mapping data.frame, column anonymous_read_id is the read id and column genome_id is the original bacterial genome id.

We perform Hierarchical Binning on the simulated reads, for initially 2 abundance classes. Data is analyzed with 10-mers for the AB part and with 4-mers for the following CB part. The call returns a dataframe of the assigned final hierarchical cluster (ABxCB) and distances to all clusters for each read :

assignments.ABxCB <- hierarchical_binning(
        system.file("extdata","reads.metagenome.fasta.gz",package ="metabinR"),
        numOfClustersAB = 2,
        kMerSizeAB = 10,
        kMerSizeCB = 4, 
        dryRun = TRUE, 
        outputC = "vignette") %>%
    arrange(read_id)

Note that read id of fasta header matches anonymous_read_id of reads.mapping.

Calculate Vmeasure and other an extrinsic measures like Homogeneity and completeness.

eval.ABxCB.sabre <- sabre::vmeasure(as.character(assignments.ABxCB$ABxCB),
                                    as.character(reads.mapping$genome_id))
tab <- as.data.frame(
    c(
        Vmeasure = round(eval.ABxCB.sabre$v_measure,4),
        Homogeneity = round(eval.ABxCB.sabre$homogeneity,4),
        Completeness = round(eval.ABxCB.sabre$completeness,4)
    )
)
knitr::kable(tab, caption = "ABxCB binning evaluation", col.names = NULL)

Table 3: ABxCB binning evaluation
Vmeasure 0.2830
Homogeneity 0.4722
Completeness 0.2021

Clean files :

unlink("vignette__*")

7 Session Info

utils::sessionInfo()
#> R version 4.4.1 (2024-06-14)
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#> [1] sabre_0.4.3       cvms_1.6.2        gridExtra_2.3     ggplot2_3.5.1    
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