Ecophysiological Properties and Hydrolytic Activity of Chemoorganotrophic Bacteria from Holosiivskyi National Nature Park

Abstract

Any natural ecosystem contains a specific range of microorganisms. The anthropogenic impact can cause a change in the growth conditions of soil and rhizospheric microbiome and affect the number and the physiological properties of microorganisms. The aim of the study was to isolate the representative microorganisms from terrestrial ecosystems of Holosiivskyi National Nature Park (Ukraine) that are not exposed to extreme factors, to study their ecophysiological properties (resistance to UV radiation, dehydration, hypersalinity, temperature), and to study the extracellular glycoside and proteolytic activities. Methods. Aerobic chemoorganotrophic bacteria isolated at 30°C from soil and phytocenoses of Holosiivskyi National Nature Park were studied. Meat-peptone agar was used to cultivate bacteria. Bacterial UV irradiation was performed with a BUF-15 lamp (λ=254 nm) in the range of 30—1350 J/m2. The temperature range of growth and halotolerance of microorganisms was determined in the range of 1—42°C and 0.1—150 g NaCl/L, respectively. Bacterial isolates were cultivated in submerged conditions at 28°C for 4 days. Synthetic p-nitrophenyl substrates, soluble starch, and guar galactomannan were used to determine glycosidase activity. To study proteolytic activity, casein, elastin, and gelatin were used. Results. The study of 14 soil and plant samples revealed the number of bacteria detected from 9.3×104 to 4.8×105 CFU/g in winter, and 4.8×105 to 4.2×106 CFU/g in summer. The microorganisms were represented by 1—4 morphotypes. There were isolated 37 isolates of aerobic chemoorganotrophic microorganisms, and 69% of them were represented by gram-positive rods. Th e dominance of pigmented isolates was not detected. Most of the microorganisms studied were psychrotolerant and moderate halophiles. The isolates 3g3, 8g1, 8g2, 8g3 from chornozem and dark gray soil showed high resistance to UV radiation. Th e LD99.99 ranged from 800 to 1100 J/m2. The isolates from chornozem, birch moss, green moss with sand and soil, and green moss from oak (1g, 4g2, 9g1, 14g2) were moderately resistant. The LD99.99 was 280—650 J/m2. The UV resistance was shown to be independent of pigmentation. It correlated with dehydration. The phenomenon of resistance to such UV radiation and dehydration may indicate the presence of active reparation mechanisms of DNA damage. All isolates showed cellulose and hemicellulose degrading activities as well as caseinolytic activity. Isolate 9g1 showed high β-xylosidase activity. Conclusions. The high resistance to UV radiation and dehydration of non-adapted microorganisms as well as the wide range of exohydrolase activity indicate the wide adaptive capacity of microorganisms from natural ecosystems, which goes beyond the influence of surrounding factors. No data existed in the available literature defining hydrolytic activity and resistance of microorganisms of the temperate region of Ukraine to extreme factors. The obtained experimental data will allow for a better understanding of the resistance level of microorganisms of temperate regions to extreme factors. As a result of the work, new bacteria with high degrading activity were isolated. The studied isolates require further characterization and analysis for biotechnological applications.