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The Black Sea estuaries represent interfaces of the sea and river environments. Microorganisms that inhabit estuarine water play an integral role in all biochemical processes that occur there and form unique ecosystems. There are many estuaries located in the Southern-Western part of Ukraine and some of them are already separated from the sea. The aim of this research was to determine the composition of microbial communities in the Khadzhibey, Dniester and Sukhyi estuaries by metagenomic 16S rDNA analysis. This study is the first complex analysis of estuarine microbiota based on isolation of total DNA from a biome that was further subjected to sequencing. DNA was extracted from water samples and sequenced on the Illumina Miseq platform using primers to the V4 variable region of the 16S rRNA gene. Computer analysis of the obtained raw sequences was done with QIIME (Quantitative Insights Into Microbial Ecology) software. As the outcome, 57970 nucleotide sequences were retrieved. Bioinformatic analysis of bacterial community in the studied samples demonstrated a high taxonomic diversity of Prokaryotes at above genus level. It was shown that majority of 16S rDNA bacterial sequences detected in the estuarine samples belonged to phyla Cyanobacteria, Proteobacteria, Bacteroidetes, Actinobacteria, Verrucomicrobia, Planctomycetes. The Khadhzibey estuary was dominated by the Proteobacteria phylum, while Dniester and Sukhyi estuaries were characterized by dominance of Cyanobacteria. The differences in bacterial populations between the Khadzhibey, Dniester and Sukhyi estuaries were demonstrated through the Beta-diversity analysis. It showed that the Khadzhibey estuary's microbial community significantly varies from the Sukhyi and Dniester estuaries. The majority of identified bacterial species is known as typical inhabitants of marine environments, however, for 2.5% of microbial population members in the studied estuaries no relatives were determined.

In recent years researchers have attracted their attention to such glycosidases as α-L-rhamnosidase (α-L-rhamnoside-rhamnohydrolase – EC 3.2.1.40). The substrates of their action are widespread in the plant world glycosides such as naringin, quercetrin, hesperidin, neohesperidin, and rutin, from which α-L-rhamnosidases cleave the terminal unreduced L-rhamnose residues. This specificity of α-L-rhamnosidases can be used in various industries: food – to improve the quality of drinks (reducing bitterness in citrus juices, enhancing the aroma of wines), as well as production of food additives; in the pharmaceutical industry – to improve the biological properties of bioflavonoids, in particular anti-inflammatory. A number of them are characterized by cardio- and radioprotective effects, have antioxidant, cytotoxic, antibacterial, antisclerotic properties, and are used in the complex treatment of coronary heart disease, including angina pectoris. The use of α-L-rhamnosidases in the chemical industry is associated with a reduction in the cost of rhamnose production as well as various plant glycosides and rutinosides. In the literature available to us, no data were found on the producers of α-L-rhamnosidases among the representatives of actinobacteria, which are known to synthesize a wide range of biologically active compounds, including antibiotics and enzymes. Purpose. To study the ability of actinobacteria isolated from water and bottom sediments of the Black Sea, to produce a-L-rhamnosidase, and also to study the properties of the most active producer. Methods. Glycosidase activity was determined by the Romero and Davis methods, protein – by the Lowry method. Results. The study of 12 glycosidase activities in 10 strains of actinobacteria isolated from bottom sediments of the Black Sea indicated that 6 investigated strains showed the ability to synthesize an enzyme with a-L-rhamnosidase and b-D-glucosidase activity. Studies have shown that the highest α-L-rhamnosidase activity (0.14 U/mg protein) was manifested by Acty 5 isolate with an optimum pH of 7.0 and a temperature optimum of 38°C. The enzyme preparation showed substrate specificity both for natural (rutin, naringin, neohesperidin) and synthetic (p-nitrophenyl derivatives of L-rhamnose and D-glucose) substrates. Conclusions. Promising Acty 5 isolate with high a-L-rhamnosidase and low b-Dglucosidase activity was found among marine actinobacteria. Bacteria with two enzymes activity expand the possibilities of their practical use.

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