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MaAsLin2 User Manual

MaAsLin2 is the next generation of MaAsLin (Microbiome Multivariable Association with Linear Models).

MaAsLin2 is comprehensive R package for efficiently determining multivariable association between clinical metadata and microbial meta-omics features. MaAsLin2 relies on general linear models to accommodate most modern epidemiological study designs, including cross-sectional and longitudinal, along with a variety of filtering, normalization, and transform methods.

If you use the MaAsLin2 software, please cite our manuscript:

Mallick et al. (2020+). "Multivariable Association Discovery in Population-scale Meta-omics Studies" (In Submission).

If you have questions, please direct it to :
MaAsLin2 Forum
Google Groups (Read only)



MaAsLin2 finds associations between microbiome multi-omics features and complex metadata in population-scale epidemiological studies. The software includes multiple analysis methods (including support for multiple covariates and repeated measures), filtering, normalization, and transform options to customize analysis for your specific study.


MaAsLin2 is an R package that can be run on the command line or as an R function.


MaAsLin2 can be run from the command line or as an R function.

If only running from the command line, you do not need to install the MaAsLin2 package but you will need to install the MaAsLin2 dependencies.

From command line

  1. Download the source:
  2. Decompress the download:
    • $ tar xzvf
  3. Install the Bioconductor dependencies edgeR and metagenomeSeq.
  4. Install the CRAN dependencies:
    • $ R -q -e "install.packages(c('lmerTest','pbapply','car','dplyr','vegan','chemometrics','ggplot2','pheatmap','hash','logging','data.table','MuMIn','glmmTMB','MASS','cplm','pscl'), repos='')"
  5. Install the MaAsLin2 package (only r,equired if running as an R function):
    • $ R CMD INSTALL maaslin2

From R

To install the latest release version of MaAsLin 2:

if(!requireNamespace("BiocManager", quietly = TRUE))

To install the latest development version of MaAsLin 2:


How to Run

MaAsLin2 can be run from the command line or as an R function. Both methods require the same arguments, have the same options, and use the same default settings.

Input Files

MaAsLin2 requires two input files.

  1. Data (or features) file
    • This file is tab-delimited.
    • Formatted with features as columns and samples as rows.
    • The transpose of this format is also okay.
    • Possible features in this file include taxonomy or genes.
  2. Metadata file
    • This file is tab-delimited.
    • Formatted with features as columns and samples as rows.
    • The transpose of this format is also okay.
    • Possible metadata in this file include gender or age.

The data file can contain samples not included in the metadata file (along with the reverse case). For both cases, those samples not included in both files will be removed from the analysis. Also the samples do not need to be in the same order in the two files.

NOTE: If running MaAsLin2 as a function, the data and metadata inputs can be of type data.frame instead of a path to a file.

Output Files

MaAsLin2 generates two types of output files: data and visualization.

  1. Data output files
    • all_results.tsv
      • This includes the same data as the data.frame returned.
      • This file contains all results ordered by increasing q-value.
      • The first columns are the metadata and feature names.
      • The next two columns are the value and coefficient from the model.
      • The next column is the standard deviation from the model.
      • The N column is the total number of data points.
      • The column is the total of non-zero data points.
      • The pvalue from the calculation is the second to last column.
      • The qvalue is computed with p.adjust with the correction method.
    • significant_results.tsv
      • This file is a subset of the results in the first file.
      • It only includes associations with q-values <= to the threshold.
    • residuals.rds
      • This file contains a data frame with residuals for each feature.
    • fitted.rds
      • This file contains a data frame with fitted values for each feature.
    • ranef.rds
      • This file contains a data frame with extracted random effects for each feature (if random effects are specified).
    • maaslin2.log
      • This file contains all log information for the run.
      • It includes all settings, warnings, errors, and steps run.
  2. Visualization output files
    • heatmap.pdf
      • This file contains a heatmap of the significant associations.
    • [a-z/0-9]+.pdf
      • A plot is generated for each significant association.
      • Scatter plots are used for continuous metadata.
      • Box plots are for categorical data.
      • Data points plotted are after normalization, filtering, and transform.

Run a Demo

Example input files can be found in the inst/extdata folder of the MaAsLin2 source. The files provided were generated from the HMP2 data which can be downloaded from .

HMP2_taxonomy.tsv: is a tab-demilited file with species as columns and samples as rows. It is a subset of the taxonomy file so it just includes the species abundances for all samples.

HMP2_metadata.tsv: is a tab-delimited file with samples as rows and metadata as columns. It is a subset of the metadata file so that it just includes some of the fields.

Command line

$ Maaslin2.R --transform=AST --fixed_effects="diagnosis,dysbiosisnonIBD,dysbiosisUC,dysbiosisCD,antibiotics,age" --random_effects="site,subject" --normalization=NONE --standardize=FALSE inst/extdata/HMP2_taxonomy.tsv inst/extdata/HMP2_metadata.tsv demo_output

  • Make sure to provide the full path to the MaAsLin2 executable (ie ./R/Maaslin2.R).
  • In the demo command:
    • HMP2_taxonomy.tsv is the path to your data (or features) file
    • HMP2_metadata.tsv is the path to your metadata file
    • demo_output is the path to the folder to write the output

In R

input_data <- system.file(
    'extdata','HMP2_taxonomy.tsv', package="Maaslin2")
input_metadata <-system.file(
    'extdata','HMP2_metadata.tsv', package="Maaslin2")
fit_data <- Maaslin2(
    input_data, input_metadata, 'demo_output', transform = "AST",
    fixed_effects = c('diagnosis', 'dysbiosisnonIBD','dysbiosisUC','dysbiosisCD', 'antibiotics', 'age'),
    random_effects = c('site', 'subject'),
    normalization = 'NONE',
    standardize = FALSE)
Session Info

Session info from running the demo in R can be displayed with the following command.



Run MaAsLin2 help to print a list of the options and the default settings.

$ Maaslin2.R --help Usage: ./R/Maaslin2.R [options] <data.tsv> <metadata.tsv> <output_folder>

Options: -h, --help Show this help message and exit

    The minimum abundance for each feature [ Default: 0 ]   

    The minimum percent of samples for which a feature 
    is detected at minimum abundance [ Default: 0.1 ]

-b MIN_VARIANCE, --min_variance=MIN_VARIANCE
   Keep features with variance greater than
   [ Default: 0.0 ]

    The q-value threshold for significance [ Default: 0.25 ]

    The normalization method to apply [ Default: TSS ]
    [ Choices: TSS, CLR, CSS, NONE, TMM ]

    The transform to apply [ Default: LOG ]
    [ Choices: LOG, LOGIT, AST, NONE ]

    The analysis method to apply [ Default: LM ]
    [ Choices: LM, CPLM, NEGBIN, ZINB ]

    The random effects for the model, comma-delimited
    for multiple effects [ Default: none ]

    The fixed effects for the model, comma-delimited
    for multiple effects [ Default: all ]

    The correction method for computing the 
    q-value [ Default: BH ]

    Apply z-score so continuous metadata are 
    on the same scale [ Default: TRUE ]

-l PLOT_HEATMAP, --plot_heatmap=PLOT_HEATMAP
    Generate a heatmap for the significant 
    associations [ Default: TRUE ]

-i HEATMAP_FIRST_N, --heatmap_first_n=HEATMAP_FIRST_N
    In heatmap, plot top N features with significant 
    associations [ Default: TRUE ]

-o PLOT_SCATTER, --plot_scatter=PLOT_SCATTER
    Generate scatter plots for the significant
    associations [ Default: TRUE ]

-e CORES, --cores=CORES
    The number of R processes to run in parallel
    [ Default: 1 ]

    The factor to use as a reference for a variable 
    with more than two levels provided as a string 
    of 'variable,reference' semi-colon delimited 
    for multiple variables [ Default: NA ] 
    NOTE: A space between the variable and reference
    will not error but will cause an inaccurate result.


  1. Question: When I run from the command line I see the error Maaslin2.R: command not found. How do I fix this?
    • Answer: Provide the full path to the executable when running Maaslin2.R.
  2. Question: When I run as a function I see the error Error in library(Maaslin2): there is no package called 'Maaslin2'. How do I fix this?
    • Answer: Install the R package and then try loading the library again.
  3. Question: When I try to install the R package I see errors about dependencies not being installed. Why is this?
    • Answer: Installing the R package will not automatically install the packages MaAsLin2 requires. Please install the dependencies and then install the MaAsLin2 R package.