Известия высших учебных заведений. Поволжский регион: Естественные науки (Mar 2022)
The effect of lignin degradation products on the dynamics of mycelial fungi complex under the model conditions
Abstract
Background. Overexploitation of soil as a productive resource, which is observed almost everywhere at the present time, leads to depletion of humus reserves, which, in turn, is the most important factor of fertility. In natural cenosis, this problem is not so significant, since humus reserves are in a state of relative dynamic equilibrium. This is achieved due to the constant flow of dead plant organic matter into the soil and the coordinated activity of a complex of microorganisms, ensuring its stepwise degradation. An important place in this complex is occupied by filamentous fungi capable of enzymatic destruction of complex polymers (cellulose and, especially, lignin). On the basis of the products of their incomplete decomposition, as well as their secondary derivatives, a complex complex of phenolic compounds is formed that compose the substance of humus. The manifestation of the physiological and functional activity of soil filamentous fungi in natural conditions is associated with a whole range of external parameters: the influence of hydrological, edaphic, climatic factors, interaction with other organisms, including rhizosphere microflora, competing species, etc. Of considerable interest is the possibility of influencing the development of the fungus from its natural substrate: organic matter at different stages of decomposition, as well as intermediates formed in the process of destruction, including lignin derivatives, reactive oxygen species, and others. In the opinion of many authors, lignin and the products of its partial degradation as components of the substrate are capable of significantly influencing the development and morphogenesis of fungi. In this regard, it is of interest to study the effect of intermediate lignin decomposition products on the structure of the mycobiota complex under model conditions. The purpose of the research is to study the role of lignin intermediate as a factor providing a competitive advantage of zymogenic and autochthonous mycobiota at different stages of destruction of plant organic matter. Materials and methods. The objects of the study were strains of filamentous fungi Trichoderma viride Pers (TV-18), Aspergillus terreus Thom (Ater-12), Penicillium chrysogenum Thom (Pch-19), isolated from gray forest soils of the Penza region and maintained in the collection of mycelial cultures of the Penza State Agrarian University. The cultivation of the mycelium was carried out on Hutchinson’s medium according to generally accepted methods. The experiments were carried out using a typical intermediate product of lignin degradation – syringaldehyde containing 34 % of methoxyl groups (-OCH3) in its composition. The degree of utilization of the specified product by the mycelium was judged by the dynamics of the content of methoxyl groups in the medium. The determination of the content of methoxyl groups in the substrates was carried out by the Zeisel method in modification with the use of gas-liquid chromatography. The development parameters of mycelial cultures were assessed by the average growth rate of mycelium, as well as by the intensity of ergosterol synthesis, as an illustration of the preparation of the culture for secondary metabolism. 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 the program for data processing and analysis “Statistica 6.0”. Results. Studies of the dynamics of development of cultures of filamentous fungi Trichoderma viride Pers (TV-18), Aspergillus terreus Thom (Ater-12), Penicillium chrysogenum Thom (Pch-19) were carried out under individual and joint cultivation under model conditions in the presence of syringaldehydeat different stages of destruction. It was found that during individual cultivation, the influence on the development of T. viride from the syringaldehyde contained in the nutrient medium at a level of 0.25 % is not observed. Growth rate, as well as cultural and morphological parameters (changes in mycelium pigmentation, timing of onset and intensity of sporulation) practically did not differ from the control variant, in which syringaldehydewas absent. The content of methoxyl groups in the nutrient medium practically did not change during the cultivation period. When studying the features of development on Hutchinson’s medium with the addition of syringaldehydein an amount of 0.25 % of the composition of the medium of A. terreus and P. chrysogenum cultures, stimulation of the growth of mycelium of fungi of both species was found, as well as the relationship between the dynamics of the content of methoxyl groups with the synthesis of ergosterol, the intensity of pigmentation of the mycelium and sporulation. The joint cultivation of the three studied species on the indicated medium made it possible to establish the suppression of the development of the T. viride culture against the background of the intensive development of A. terreus and P. chrysogenum. Moreover, in the control variant, T. viride showed itself as a strong competitor, and, due to its high growth rate, as a rule, suppressed the development of A. terreus and P. chrysogenum in the first five days of cultivation. Conclusions. The features of the development of common soil mycobiota species, which make a significant contribution to the course of soil-forming processes, have been studied under model conditions in the presence of a lignin degradation product rich in methoxyl groups – syringaldehyde. In experiments, the role of this component of the nutrient medium as a factor providing competitive advantages to autochthonous mycobiota was established. It can be assumed that the presence of a product of lignin destruction can act as a selection factor that determines the competitive potential of mycobiota and the functional activity of its components at different stages of the soil-forming process. Considering that syringaldehyde and similar phenolic compounds are components of an irregular lignin molecule released in humification processes, it is possible to assume the existence of similar mechanisms in natural conditions.
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