The effect of lignin degradation products on the dynamics of mycelial fungi complex under the model conditions

Background. Overexploitation of soil as a productive resource, which is observedalmost 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 tothe constant flow of dead plant organic matter into the soil and the coordinated activity ofa complex of microorganisms, ensuring its stepwise degradation. An important place in thiscomplex is occupied by filamentous fungi capable of enzymatic destruction of complexpolymers (cellulose and, especially, lignin). On the basis of the products of their incompletedecomposition, as well as their secondary derivatives, a complex complex of phenoliccompounds is formed that compose the substance of humus. The manifestation of the physiologicaland functional activity of soil filamentous fungi in natural conditions is associatedwith a whole range of external parameters: the influence of hydrological, edaphic, climaticfactors, interaction with other organisms, including rhizosphere microflora, competingspecies, etc. Of considerable interest is the possibility of influencing the developmentof 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 productsof its partial degradation as components of the substrate are capable of significantly influencingthe development and morphogenesis of fungi. In this regard, it is of interest to studythe effect of intermediate lignin decomposition products on the structure of the mycobiotacomplex under model conditions. The purpose of the research is to study the role of ligninintermediate as a factor providing a competitive advantage of zymogenic and autochthonousmycobiota at different stages of destruction of plant organic matter. Materials andmethods. The objects of the study were strains of filamentous fungi Trichoderma viridePers (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 mycelialcultures of the Penza State Agrarian University. The cultivation of the mycelium wascarried out on Hutchinson’s medium according to generally accepted methods. The experimentswere carried out using a typical intermediate product of lignin degradation – syringaldehydecontaining 34 % of methoxyl groups (-OCH3) in its composition. The degree ofutilization of the specified product by the mycelium was judged by the dynamics of thecontent of methoxyl groups in the medium. The determination of the content of methoxylgroups in the substrates was carried out by the Zeisel method in modification with the useof gas-liquid chromatography. The development parameters of mycelial cultures wereassessed by the average growth rate of mycelium, as well as by the intensity of ergosterolsynthesis, 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 gaschromatography with derivatization of the unsaponifiable fraction of lipids extracted fromthe mycelium by the Folch method into trimethylsilyl derivatives. Statistical processing wascarried out using the program for data processing and analysis “Statistica 6.0”. Results.Studies of the dynamics of development of cultures of filamentous fungi Trichodermaviride Pers (TV-18), Aspergillus terreus Thom (Ater-12), Penicillium chrysogenum Thom(Pch-19) were carried out under individual and joint cultivation under model conditions inthe presence of syringaldehydeat different stages of destruction. It was found that duringindividual cultivation, the influence on the development of T. viride from the syringaldehydecontained in the nutrient medium at a level of 0.25 % is not observed. Growth rate, aswell as cultural and morphological parameters (changes in mycelium pigmentation, timingof onset and intensity of sporulation) practically did not differ from the control variant, inwhich syringaldehydewas absent. The content of methoxyl groups in the nutrient mediumpractically did not change during the cultivation period. When studying the features of developmenton Hutchinson’s medium with the addition of syringaldehydein an amount of0.25 % of the composition of the medium of A. terreus and P. chrysogenum cultures, stimulationof 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 cultivationof 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 intensivedevelopment 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 beenstudied under model conditions in the presence of a lignin degradation product rich inmethoxyl groups – syringaldehyde. In experiments, the role of this component of the nutrientmedium as a factor providing competitive advantages to autochthonous mycobiota wasestablished. It can be assumed that the presence of a product of lignin destruction can act asa selection factor that determines the competitive potential of mycobiota and the functionalactivity of its components at different stages of the soil-forming process. Considering thatsyringaldehyde and similar phenolic compounds are components of an irregular lignin moleculereleased in humification processes, it is possible to assume the existence of similarmechanisms in natural conditions.