EXPERT - a scalable model for quantifying source contributions for microbial communities

Challenges remain to be addressed in terms of quantifying source origins for microbiome samples in a fast, comprehensive, and context-aware manner. Traditional approaches to such quantification have severe trade-offs between efficiency, accuracy, and scalability.

Here, we introduce EXPERT, a scalable community-level microbial source tracking approach. Built upon the biome ontology information and transfer learning techniques, EXPERT has acquired the context-aware flexibility and could easily expand the supervised model's search scope to include the context-depende/nt community samples and understudied biomes. While at the same time, it is superior to current approaches in source tracking accuracy and speed. EXPERT's superiority has been demonstrated on multiple source tracking tasks, including source tracking samples collected at different disease stages and longitudinal samples. For details refer to our original study.

Supervised learning (with high efficiency and accuracy) meets transfer learning (with inherent high scalability), towards better understanding the dark matters in microbial community.

Support

For support using EXPERT, please contact us.

This is our beta version, any comments or insights would be greatly appreciated.

Features

1. Context-aware ability to adapt to microbiome studies via transfer learning
2. Fast, accurate and interpretable source tracking via ontology-aware forward propagation
3. Supports both amplicon sequencing and whole-genome sequencing data.
4. Selective learning from partially-labeled training data
5. Ultra-fast data cleaning & cleaning via in-memory NCBI taxonomy database
6. Parallelized feature encoding via tensorflow.keras

Installation

You can simply install EXPERT using pip package manager.

pip install expert-mst    # Install EXPERT
expert init               # Initialize EXPERT and install NCBI taxonomy database

Quick start

Here we quickly go-through basic functionalities of EXPERT through a case study, which have already been conducted in our preprinted paper. We also provided more functional show-cases in another repository.

Things to know before starting

1. EXPERT's fantastic function is its automatic generalization of fundamental models, which allows non-deep-learning users to modify the models just in terminal, without the need of any programming skill. Here we generalize a fundamental model for monitoring the progression of colorectal cancer (CRC) and assess the performance of the generalized model. We only use the disease model trained for quantifying contribution from hosts with different disease-associated biomes (refer to our preprint for details).

2. Microbial source tracking: Bayesian community-wide culture-independent microbial source tracking | Nature Methods

3. Cross-validation: Cross-validation (statistics) - Wikipedia

Get prepared

Please follow our instructions below and make sure all these commands were run on Linux/Mac OSX platform. You may also need to install Anaconda before starting.

• Install expert-mst version 0.2 (suggested).

pip install https://github.com/HUST-NingKang-Lab/EXPERT/releases/download/v0.2/expert-0.2_cpu-py3-none-any.whl
expert init

• Download the fundamental model and dataset to be used. Here CM is a abbreviation term of countMatrix, which is a format of abundance data (each row represents a taxon, and each column represents a sample/run). Mapper is another important input of EXPERT, which records source biomes for input samples.

wget -c https://github.com/HUST-NingKang-Lab/EXPERT/releases/download/v0.2-m/disease_model.tgz
tar zxvf disease_model.tgz  # Decompress the fundamental model.
for file in {QueryCM.tsv,SourceCM.tsv,QueryMapper.csv,SourceMapper.csv}; do 
    wget -c https://raw.githubusercontent.com/HUST-NingKang-Lab/EXPERT/master/data/$file;
done

Preprocess the dataset

• Construct a biome ontology representing stages of CRC. You'll see constructed ontology like a tree in the printed message.

grep -v "Env" SourceMapper.csv | awk -F ',' '{print $6}' | sort | uniq > microbiomes.txt
expert construct -i microbiomes.txt -o ontology.pkl

• Map microbial community samples to the biome ontology to obtain hierarchical labels. You'll see counts of the samples on each biome ontology layer in the printed message.

expert map --to-otlg -i SourceMapper.csv -t ontology.pkl -o SourceLabels.h5
expert map --to-otlg -i QueryMapper.csv -t ontology.pkl -o QueryLabels.h5

• Convert input abundance data to model-acceptable hdf file. The EXPERT model only accepts standardized abundance data. Here we standardize the abundance data using convert mode.

ls SourceCM.tsv > inputList; expert convert -i inputList -o SourceCM.h5 --in-cm;
ls QueryCM.tsv > inputList; expert convert -i inputList -o QueryCM.h5 --in-cm;
rm inputList

Modeling and evaluation

• Transfer knowledge about disease (from the disease model) to the CRC model, for a better performance on the CRC monitoring. You'll see running log and training process in the printed message.

expert transfer -i SourceCM.h5 -l SourceLabels.h5 -t ontology.pkl -m disease_model -o CRC_model

• Search the query samples against the model.

expert search -i QueryCM.h5 -m CRC_model -o quantified_source_contributions

• Evaluate the performance of the CRC model. You'll obtain a performance report on each stage of CRC.

expert evaluate -i quantified_source_contributions -l QueryLabels.h5 -o performance_report
cat performance_report/overall.csv

You now have acquired skills of EXPERT modeling for microbial source tracking. Next, you may want to explore a question: Which fundamental model gives the best performance on the CRC monitoring? You may want to assess the performance utilizing another fundamental model. Good luck.

Advanced usage

EXPERT has enabled the adaptation to context-dependent studies, in which you can choose potential sources to be estimated. Please follow our documentation: advanced usage.

Model resources

Note: These models were trained on EXPERT version 0.2.

How-to-cite

If you are using EXPERT in a scientific publication (or inspired by the approach), we would appreciate citations to the following paper:

Hui Chong, Yuguo Zha, Qingyang Yu, Mingyue Cheng, Guangzhou Xiong, Nan Wang, Xinhe Huang, Shijuan Huang, Chuqing Sun, Sicheng Wu, Wei-Hua Chen, Luis Pedro Coelho, Kang Ning*. EXPERT: transfer learning-enabled context-aware microbial community classification. Briefings in Bioinformatics, 2022; bbac396. doi:10.1093/bib/bbac396.

Maintainer