What is OrthoANI?

OrthoANI (Orthologous Average Nucleotide Identity) is a kind of similarity value between two genome sequences. It is an improved version of the original ANI (Average Nucleotide Identity) and is one of the OGRIs. It can be used for classification and identification of Bacteria, and the proposed cutoff for species boundary is 95~96%. The algorithm was published by Lee et al. (2015). Later, we developed a faster version, named OrthiANIu, using USEARCH program instead of BLAST. The software tools are available as a web service and standalone program.

  • To calculate OrthoANIu between two genomes, visit here.

  • To download the standalone program, visit here.

OrthoANIu is the standard algorithm used to build the EzBioCloud database. The publication for the OrthoANIu tool is available here.

How is it different from ANI?

The major differences between the original ANI and OrthoANI are:

  • For the original ANI, you need to obtain the reciprocal values (i.e., A->B & B->A), and use the mean value for taxonomic use. In contrast, you only need a single value (A<->B) for OrthoANI.

  • OrthoANI is faster than the original ANI.


Lee, I., Ouk Kim, Y., Park, S. C., & Chun, J. (2016). OrthoANI: an improved algorithm and software for calculating average nucleotide identity. International journal of systematic and evolutionary microbiology, 66(2), 1100-1103.

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