Chitinases (EC 3.2. 1.14) are hydrolytic enzymes which play the key role in the degradation of chitin, one of the most common polysaccharides (Gooday, 1990). They are used in a broad spectrum of biotechnological applications, from biomass conversion into agricultural products to technologies for production of pharmaceutically important chitooligosaccharides. Chitinases are secreted enzymes. Their structures should be therefore adapted to environmental conditions, which implies the importance of analysis of chitinases and their producers in microbial ecology studies. An overwhelming majority of chitinases belongs to two families of glycoside hydrolases, GH18 and GH19, which differ in amino acid sequence, tertiary structure, and catalytic mechanisms (Iseli et al., 1996). While the majority of characterized chitinases of the GH19 family have been isolated from plants and bacteria, fungal chitinases of this family were recently described (Han et al., 2016). GH18, being much better studied family of glycoside hydrolases, is characterized by much higher diversity and number of producers. Thus, according to the CAZy database (www. cazy. org), 57 archaeal, 6125 bacterial, 2815 eukaryotic, and 232 viral chitinases of the GH18 family are presently known. The GH18 chitinases form three deep phylogenetic lineages corresponding to three major conventional groups, A (сhiA), B (сhiВ) and C (сhiC)(Suzuki et al., 1999). Group A is the largest, with its representatives often detected in various environments. Some authors proposed therefore to use the сhiA gene as a phylogenetic marker of diversity of chitinolytic prokaryotes (Hobel et al., 2005; Cretoiu et al., 2012). Marine environments are characterized by massive biosynthesis and biodegradation of chitin, which is produced mainly by the zooplankton (Keyhani and Roseman, 1999) and is utilized mainly by benthic microorganisms (Poremba, 1995). Phylogenetic analysis of the ChiA gene in microbial communities of bottom sediments revealed considerable diversity of chitinolytic microorganisms in different basins of the World Ocean (Le Cleir et al., 2004; Xiao et al., 2005; Lian et al., 2007).

The special position of the Baltic Sea in the system of the World Ocean is due to its glacial origin and low salinity (for its central part form 7–8‰ at the surface to 11–12‰ in deeper layers) caused by pronounced river runoff (Stigebrandt, 2001). This factor probably contributes significantly to formation of microbial communities of the sediments and the water column (Riemann et al., 2008).