indel, in out-group species (viz. Archaea), it can be inferred whether the indel is an insert or a deletion, and which of these two groups A, B, C or X, Y, Z is ancestral.

Mainline CSIs have been used in the past to determine the phylogenetic relationship of a number of bacterial phyla. The large CSI of about 150-180 amino acids within a conserved region of Gyrase B (between amino acids 529-751), is commonly shared between various Pseudomonadota, Chlamydiota,