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UST is a bioinformatics tool for constructing a spectrum-preserving string set (SPSS) representation from sets of k-mers.

Note: This software has been subsumed by ESSCompress. To use UST, download ESSCompress and follow the UST instructions in the README.


GCC >= 4.8 or a C++11 capable compiler

Quick start

To install, compile from source:

git clone
cd UST

After compiling, use

./ust -i [unitigs.fa] -k [kmer_size]


./ust -i examples/k11.unitigs.fa -k 11

The important parameters are:

  • k [int] : The k-mer size that was used to generate the input, i.e. the length of the nodes of the node-centric de Bruijn graph.
  • i [input-file] : Unitigs file produced by BCALM2 in FASTA format.
  • a [0 or 1] : Default is 0. A value of 1 tells UST to preserve abundance. Use this option when the input file was generated with the -all-abundance counts option of BCALM2.

The output is a FASTA file with extenstion "ust.fa" in the working folder, which is the SPSS representaiton of the input. If the program is run with the option -a 1, an additional count file with extension "ust.counts" will also be generated.

Detailed Usage

In order to build a SPSS representation for your k-mer set, you must first run BCALM2 on your set of k-mers. BCALM2 will construct a set of unitigs. Those unitigs are then fed as input to ust, which outputs a FASTA file with the SPSS representation. Note that the k parameter to ust must match the -kmer-size used when running BCALM2.

If you would like to store the data on disk in compressed form (like UST-Compress in our paper), you can then install and run MFCompress on the output of UST as follows: MFCompressC mykmers.ust.fa

If you would like to build a membership data structure based on UST, then

  • Install bwtdisk and dbgfm.
  • Change the two variables "DBGFM_DIRECTORY" and "BWTDISK_DIRECTORY" in the script to point to the locations where dbgfm and bwtdisk are installed. Alternatively, you can add the path to both tools in your environment PATH variable and then modify the script accordingly.
  • Run as follows: mykmers.ust.fa


If using UST in your research, please cite

  author    = {Amatur Rahman and Paul Medvedev},
  title     = {Representation of $k$-mer sets using spectrum-preserving string sets},
  booktitle = {Research in Computational Molecular Biology - 24th Annual International Conference, {RECOMB} 2020, Padua, Italy, May 10-13, 2020, Proceedings},
  series    = {Lecture Notes in Computer Science},
  volume    = {12074},
  pages     = {152--168},
  publisher = {Springer},
  year      = {2020

Note that the general notion of an SPSS was independently introduced under the name of simplitigs. Therefore, if citing this general notion, please also cite:


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