ADAPTATION OF ASPERGILLUS TERREUS THOM STRAINS TO SALINE STRESS IN THE PRESENCE OF PHENOL COMPOUNDS IN SIMULATED CONDITIONS

Abstract

Backgrounds. Fungi of the genus Aspergillus are stable residents of soil microbocenoses, are part of endophytic complexes of plant root systems, and play an important role in the processes of decomposition of lignocellulose complexes and humification. Dynamic balance and soil fertility are inextricably linked with the normal functioning of microbiocenoses. According to modern data, disturbed lands occupy vast areas in the world, in particular, saline soils – about 25 % of the entire land surface. In this regard, the aspects of adaptation of representatives of the resident microflora to the action of chemical stressors of the environment are of interest. The aim of this work is to assess the role of phenolic compounds – components of lignin molecules in the formation of resistance of cultures of the genus Aspergillus under conditions of salt stress under model conditions. Materials and methods. The objects of the study were strains of the filamentous fungus Aspergillus terreus Thom: At-09, Ater-12, Ater (Pnz)-12. The cultivation of the mycelium was carried out according to generally accepted methods. Salt stress for the cultures was created by adding sodium chloride to the nutrient medium in an amount of 0,5 M of the medium weight. Determination of the level of oxidative stress in the cultures was carried out using the determination of the marker compound – malondialdehyde (MDA). To determine the concentration of malondialdehyde (MDA) in the mycelium, the method of M. Michara et al. (1980) was used, based on the interaction of MDA and thiobarbituric acid (TBA). To assess the peroxidase activity of the mycelium, CAS-No.90-05-1 guaiacol (metox-syphenol) was used, which was introduced into the extract from the mycelium at a concentration of 0,4 mM. The peroxidase activity of the mycelium was judged by the change in the color of the nutrient medium, which illustrates the oxidation of guaiacol to quinone. The determination of the content of ergosterol in the mycelium was carried out by gas chromatography with derivatization of the unsaponifiable fraction of lipids extracted from the mycelium by the Folch method into trimethylsilyl derivatives. Statistical processing was carried out using “Statistica 6.0” program for data processing and analysis. Results. The results of studies of the effect of salt stress on the state of A. terreus mycelium revealed the manifestation of different degrees of pronounced signs of stress in the cultures of the studied strains. The complete inhibition of the development of cultures of the strains of the studied species with the content of 0,5 M sodium chloride in the medium was not noted, however, the inhibition in the development of the mycelium, as well as the accumulation of malondialdehyde in the mycelium, was significantly (in 2,96; 2,77 and 3,51 times in the studied strains) exceeding the control values. The peroxidase activity of mycelium was studied under stress conditions and in the presence of model phenolic compounds – hydrogen donors. The experiments carried out made it possible to establish a noticeable stimulation of the peroxidase activity of mycelium, which develops under conditions of saline stress in the presence of a model phenolic compound (lilac aldehyde) in the nutrient medium. It was found that in the presence of the specified compound in the experimental variants, the peroxidase activity indicators of the mycelium of the studied strains varied from 2,86 to 4,41 units. · 100/g · s and exceed by 1,3 and more times those in the control. It was also established that the presence of a model phenolic compound in the medium has a positive effect on the accumulation of mycelium biomass (2,4–2,6 times as compared with the variant of salt stress without a model phenolic compound in the medium). In the obtained weighed portions of the biomass, the content of ergosterol was determined. The content of ergosterol does not directly depend on the degree of biomass accumulation, and the percentage of ergosterol is significantly higher in the mycelium under stress (from 1,9 to 2,3 times). It was found that the accumulation of ergosterol in the mycelium of a culture under stress occurs at late stages of development, which indicates an earlier transition of the culture under stress to secondary metabolism. Conclusions. The role of a model phenolic compound (lilac aldehyde) is noted, which, on the one hand, can act as a hydrogen donor for neutralizing peroxides, providing an increase in the activity of peroxidases, which indirectly indicates the inclusion of adaptation mechanisms in the mycelium, and on the other hand, promotes activation of metabolic processes in fungoid isolates. Considering that lilac aldehyde and similar phenolic compounds (parahydroxybenzaldehyde, vanillin) are components of an irregular lignin molecule released in humification processes, it is possible to assume the existence of similar mechanisms in natural conditions.

Keywords

• aspergillus terreus
• filamentous fungi
• fungal ecology
• phenolic compounds
• adaptive potential
• oxidative stress
• salt tolerance