Bactria: BarCode TRee Inference and Analysis

This repository contains code and data for building very large, topologically-constrained barcode phylogenies through a divide-and-conquer strategy. Such trees are useful as reference materials for curating barcode data by detecting rogue terminals (indicating incorrect taxonomic annotation) and in the comparable calculation of alpha and beta biodiversity metrics across metabarcoding assays.

The input data for the approach we develop here currently comes from BOLD data dumps. The international database BOLD Systems contains DNA barcodes for hundreds of thousands of species, with multiple barcodes per species. The data dumps we use here are TSV files whose columns conform to the nascent BCDM (barcode data model) vocabulary. As such, other data sources that conform to this vocabulary could in the future be used as well, such as UNITE.

Theoretically, such data could be filtered and aligned per DNA marker to make phylogenetic trees. However, there are two limiting factors: building very large phylogenies is computationally intensive, and barcodes are not considered ideal for building big trees because they are short (providing insufficient signal to resolve large trees) and because they tend to saturate across large patristic distances.

Both problems can be mitigated by using the Open Tree of Life as a further source of phylogenetic signal. The BOLD data can be split into chunks that correspond to Open Tree of Life clades. These chunks can be made into alignments and subtrees. The OpenTOL can be used as a constraint in the algorithms to make these. The chunks are then combined in a large synthesis by grafting them on a backbone made from exemplar taxa from the subtrees. Here too, the OpenTOL is a source of phylogenetic constraint.

In this repository this concept is developed for both animal species and plant species.

Installation

The pipeline and its dependencies are managed using conda. On a linux or osx system, you can follow these steps to set up the bactria Conda environment using an environment.yml file and a requirements.txt file:

1. Clone the Repository:
   Clone the repository containing the environment files to your local machine:

   git clone https://github.com/naturalis/barcode-constrained-phylogeny.git
   cd barcode-constrained-phylogeny
   

2. Create the Conda Environment: Create the bactria Conda environment using the environment.yml file with the following command:

   conda env create -f workflow/envs/environment.yml
   

   This command will create a new Conda environment named bactria with the packages specified in the environment.yml file. This step is largely a placeholder because most of the dependency management is handled at the level of individual pipeline steps, which each have their own environment specification.
3. Activate the Environment: After creating the environment, activate it using the conda activate command:

   conda activate bactria
   

4. Verify the Environment: Verify that the bactria environment was set up correctly and that all packages were installed using the conda list command:

   conda list
   

   This command will list all packages installed in the active conda environment. You should see all the packages specified in the environment.yml file and the requirements.txt file.

How to run

The pipeline is implemented using snakemake, which is available within the conda environment that results from the installation. Important before running the snakemake pipeline is to change in config/config.yaml the number of threads available on your computer. Which marker gene is used in the pipeline is also specified in the config.yaml (default COI-5P). Prior to execution, the BOLD data package to use (we used the release of 30 December 2022) must be downloaded manually and stored in the resources/ directory. If a BOLD release from another date is used the file names in config.yaml need to be updated.

How to run the entire pipeline:

snakemake -j {number of threads} --use-conda

Snakemake rules can be performed separately:

snakemake -R {Rule} -j {number of threads} --use-conda

Enter the same number at {number of threads} as you filled in previously in src/config.yaml. In {Rule} insert the rule to be performed.

Here is an overview of all the rules in the Snakefile:

(zoomed view is available here)

Repository layout

Below is the top-level layout of the repository. This layout is in line with community standards and must be adhered to. All of these subfolders contains further explanatory READMEs to explain their contents in more detail.

• config - configuration files
• doc - documentation and background literature
• logs - where log files are written during pipeline runtime
• resources - external data resources (from BOLD and OpenTree) are downloaded here
• results - intermediate and final results are generated here
• workflow - script source code and driver snakefile

License

© 2023 Naturalis Biodiversity Center

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.