**1. Introduction**

Seaweeds are a rich source of bioactive compounds particularly with regard to polysaccharides. Red seaweeds (*Rhodophyceae*) produce sulfated galactans, such as agar and carrageenan. Other sulfated polysaccharides, such as ulvans or fucans, are found in green (*Chlorophyceae*) or brown (*Phaeophyceae*) seaweeds, respectively. Non-sulfated polysaccharides, mainly laminarans and alginates, are isolated from brown seaweeds. These polysaccharides are being actively studied due to their pharmacological anti-inflammatory, antioxidant, antiviral, antitumor, immunomodulatory, anticoagulant, hypolipidemic, and prebiotic activities [1,2]. Physical-chemical properties and biological activities of their derivatives are of great interest for study. Previous works showed they have the potential to be used as bioactive molecules and functional materials in food, pharmaceutical, and cosmetic industries [3–5]. Among seaweed polysaccharides, agar and carrageenan are valuable sources of various oligosaccharides with beneficial effects for human health, and these effects depend on the degree of depolymerization [6]. The oligosaccharides, in turn, are a source of rare sugars, such as 3,6-anhydro-l-galactose (L-AHG), which has been recently suggested to be a new anticariogenic sugar [7]. Importantly, AHG-containing oligosaccharides have been reported to demonstrate anti-inflammatory, antitumor, and anticariogenic activities [8–10]. They can be also used in cosmetic dermatology for skin moisturizing and whitening [11,12].

The most eco-friendly methods for improving the yield and quality of algal polysaccharides and their derivatives are enzyme-based techniques [1,4]. Therefore, there is a demand for highly specific hydrolytic enzymes, which in turn stimulates the search for marine bacteria specialized in the degradation of various polysaccharides. Bacterial carbohydrate-active enzymes (CAZymes) are responsible for synthesis and degradation of polysaccharides as well as their derivatives [13]. They include glycoside hydrolases (GHs), glycosyltransferases (GTs), polysaccharide lyases (PLs), and carbohydrate esterases (CEs). Now, they also include auxiliary activity (AAs) enzymes and carbohydrate-binding modules (CBMs). CAZymes have been successfully used in biotechnological, medical, and industrial applications [14]. It is necessary to take into account that the CAZyme repertoire of microorganisms might be determined by both the taxonomic level and ecological niche they occupy [15]. Therefore, a comparative genomics approach provides insights into a "core" CAZome that is conserved among organisms and an organism-specific "accessory" CAZome that encodes uniquely for each particular organism enzyme.

The phylum Bacteroidetes accommodates bacteria distributed across diverse habitats, including terrestrial, aquatic, and gut ecosystems [16–20]. Marine representatives of the Bacteroidetes are involved in many biogeochemical processes and specialize in the degradation of various biopolymers [20] due to their metabolic flexibility and special enzymatic repertoires [21]. It is known that Flavobacteriia, the most numerous class of the phylum, are specialized in the degradation of algal polysaccharides [22–25]. To date, genome investigations of marine Flavobacteriia, such as *Gramella forsetii* KT0803<sup>T</sup> [26], *Cellulophaga algicola* IC166<sup>T</sup> [27], *Polaribacter* sp. Hel1\_85 [28], *Formosa agariphila* M-2Alg 35-1T [29], and *Zobellia galactanivorans* Dsij<sup>T</sup> [30], have revealed an abundance of CAZyme genes, confirming their specialization in the utilization of polysaccharides in marine environments.

Recently, *Z. galactanivorans* DsijT has been comprehensively studied and has become a model organism for polysaccharide degradation investigation among marine flavobacteria [30]. The genus *Zobellia* was created by Barbeyron et al. [31], and to date it contains five validly described representatives: *Z. galactanivorans* DsijT, *Z. uliginosa* DSM 2061T, *Z. amurskyensis* KMM 3526T, *Z. laminariae* KMM 3676T, and *Z. russellii* KMM 3677T, which were isolated from diverse ecological niches. Although many isolates have also demonstrated an ability to degrade different polysaccharides [32], little is known about the genomic organization of hydrolytic systems within the *Zobellia* genus.

In this study, we performed de novo genome sequencing of two type *Zobellia* strains to produce the first genomics analysis of the genus and provide insights into the role of the CAZyme genomic repertoire in the degradation potential of marine bacteria. Some polysaccharide degradation systems received particular attention due to their biotechnological and medical applications.

#### **2. Results and Discussion**
