**4. Conclusions**

We revealed that PL7 family alginate lyases are the most abundant among the polysaccharide lyases identified in *Zobellia* genomes. Based on phylogenomic, structural, and comparative analyses, the PL7 lyases belong to SF3, SF5, and SF6 and are involved in local and horizontal gene transfer, as well as gene duplications processes. It is most likely that an individual evolution of PL7 genes may promote Alginate Utilization System variability across the *Zobellia* genus. The PL7 alginate lyases may acquire a sub-functionalization due to diversification between in-paralogs.

**Supplementary Materials:** Figure S1: Structure-based sequence alignment of PL7 alginate lyases from subfamily SF5; Figure S2: Structure-based sequence alignment of PL7 alginate lyases from subfamily SF6; Table S1: List of accession numbers for genomes used in the phylogenomic analysis; Table S2: Identity matrix of catalytic domains from PL7 alginate lyases identified in *Zobellia* genomes; Table S3: Identifiers of PL7 and adjacent genes included in loci I–VI.

**Author Contributions:** Conceptualization, M.I. and N.C.; methodology, E.B., O.N., and N.C.; software, N.C. and G.L.; investigation, N.C., E.B., and O.N.; data curation, M.I.; writing—original draft preparation, N.C. and M.I.; writing—review and editing, M.I.; visualization, N.C.; supervision, M.I.; funding acquisition, M.I. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Unpublished genomes are available from the authors.

**Acknowledgments:** We are grateful to the anonymous reviewers and editors that have improved our manuscript.

**Conflicts of Interest:** The authors declare no conflict of interest.
