**1. Introduction**

Marine algal polysaccharides are an important nutrient source for marine bacteria. To utilize these polysaccharides, which significantly differ from terrestrial plant ones, marine bacteria have developed unusual degradation mechanisms. Key players in the degradation of complex polysaccharides are the marine *Flavobacteriia* of the phylum *Bac-teroidetes* [1,2]. The microorganisms feature different polysaccharide utilization loci (PULs), which encode a set of enzymes and other proteins involved in the breakdown of specific polysaccharides. The first recognized PULs were alginolytic operons associated with alginate utilization in marine *Bacteroidetes* [3]. The current studies of PULs are based on the sequencing of the genomes of cultured bacteria and metagenomes as a valuable resource of CAZymes and CAZyme machineries [4–10], allowing us to expand our knowledge of the bacterial degradation of algal polysaccharides.

The major bacterial players in marine polysaccharide degradation have become the subject of extensive research studies using genomic and transcriptomic approaches. Representatives of the genus *Zobellia* are marine *Flavobacteriia* and they specialize in algal polysaccharide degradation. The genus *Zobellia* was proposed by Barbeyron et al. (2001) [11]. First, the genus included two species: *Zobellia galactanivorans* and *Zobellia uliginosa*. Later, three new species were added [12]: *Zobellia russellii*, *Zobellia laminariae*, and *Zobellia amurskyensis*. To date, the five species of the genus *Zobellia* have validly published names (as listed at https://lpsn.dsmz.de/genus/zobellia, February 2021), and all originate from marine environments.

Members of the *Zobellia* genus are frequently found associated with red and brown algae [13]. *Z. galactanivorans* DsijT, a marine species isolated from a red alga, was chosen as the type species [11]. Its genome exhibits a number of adaptive features such as consumption of algal polysaccharides, resistance to algal defense, and large amounts of CAZymes and sulfatases [14]. Numerous biochemical and structural studies have begun to unveil the

**Citation:** Chernysheva, N.; Bystritskaya, E.; Likhatskaya, G.; Nedashkovskaya, O.; Isaeva, M. Genome-Wide Analysis of PL7 Alginate Lyases in the Genus *Zobellia*. *Molecules* **2021**, *26*, 2387. https:// doi.org/10.3390/molecules26082387

Academic Editor: Changsheng Zhang

Received: 11 March 2021 Accepted: 15 April 2021 Published: 20 April 2021

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complex enzyme systems for the degradation of various polysaccharides, such as agars, carrageenans, and laminarin [3,15–21].

In this work, we have applied genome-based approaches to investigate PL7 alginate lyases across the *Zobellia* genus.
