  We propose a new algorithm for merging succinct representations of de Bruijn
graphs introduced in [Bowe et al. WABI 2012]. Our algorithm is based on the
lightweight BWT merging approach by Holt and McMillan [Bionformatics 2014,
ACM-BCB 2014]. Our algorithm has the same asymptotic cost of the state of the
art tool for the same problem presented by Muggli et al. [bioRxiv 2017,
Bioinformatics 2019], but it uses less than half of its working space. A novel
important feature of our algorithm, not found in any of the existing tools, is
that it can compute the Variable Order succinct representation of the union
graph within the same asymptotic time/space bounds.
