Characterization of Novel Chitin-degrading laceyella spp. Strains from New Athos Cave (Abkhazia) Producing Thermostable Chitinases

Nine chitin-degrading isolates of moderately thermophilic bacteria with temperature optimum for growth and chitin destruction at 50–55°C were isolated from soils of the New Athos Cave (Abkhazia). Four most active bacterial cultures with chitinase production yields 0.11–0.28 U mL–1 (at 48°C) were screened from seven isolates forming aerial mycelium. Selected isolates were identified as Laceyella sp. species based on their cultural, morphological, physiological, and biochemical characteristics, as well as on phylogenetic analysis of their 16S rRNA gene sequences; these formed a cluster with L. sacchari, L. sediminis, and L. tengchongensis on the phylogenetic tree with sequence identity of 96.43–97.21%. Occurrence of isolated thermoactinomycetes in the cave was confined to tour circuit zones and the area inundated with flood waters. Laceyella spp. strains NAC-16-5 A-4 and NAC-16-5 A-5 degraded 85–100% of colloidal chitin (5 g L–1) after 96 h of submerged cultivation (48°C). Inducible synthesis of chitinolytic enzymes was observed in all selected strains and reached its maximum in the presence of crab shell chitin. The enzymatic complex of Laceyella sp. NAC-16-5 A-4 was active in pH range 4–10.5 with two optima at pH 5.5 and 7.0. While crude chitinases of all studied strains exhibited maximal activity at 60–70°C with similar temperature optima (65°C), the enzyme complexes from strains NAC-16-5 A-2 and NAC-16-5 A-4 were most stable at 70°C.