Chitin degradation by the aquatic pigment-producing bacteria of Janthinobacterium spp. from stream flows and springs of Shulgan River basin and Shulgan-Tash Cave, Southern Urals

Six chitinolytic strains of Janthinobacterium were isolated from the springs and reservoirs in Shulgan-Tash cave, which is not only one of largest caves in Southern Urals with preserved Paleolithic painting dating back to about 20,000 years, but also a final link in the karst hydrosystem of Shulgan River basin. This study aimed to characterize chitin degradation by the isolated bacteria for comprehension of their involvement in carbon cycle proceeding in the local groundwater ecosystem. The isolates varied in their colony morphology and pigmentation; five of the strains produced violacein-like pigments, while the sole isolate synthesized red pigment similar to prodigiosin. All the isolates were identified as Janthinobacterium sp. based on 16S rRNA gene sequence, where five strains were clustered with most homology to type species, J. lividum, and the single strain, IB-RH, was located separately from this group on phylogenetic trees. The studied bacteria manifested psychrotolerant properties with temperature optima of growth and chitin destruction at 22–26 °C. The isolates generally produced extracellular chitinase in range 0.14–0.18 U/mL; the maximal enzyme’s yield reached to 6–8 days. The violacein-producing strain IB-ST-GO exhibited most rapid dynamics of the chitinase secretion together with highest growth indices and degradation degree of various chitinous substrates. The noticeable chitinase production by this strain and other isolates along with their ability to colonize and assimilate diverse chitinous substrates of crustaceans’ origin as sole carbon source evidence their potential contribution in processes of chitin degradation in the karstic and non-karstic groundwaters.