Biodegradation of humic substances by microscopic filamentous fungi: chromatographic and spectroscopic proxies

  • Elena FedoseevaEmail author
  • Andrey Stepanov
  • Olga Yakimenko
  • Svetlana Patsaeva
  • Mikhail Freidkin
  • Daria Khundzhua
  • Vera Terekhova
Humic Substances and Nature-like Technologies



The study of interactions between humic substances (HSs) and soil filamentous fungi is the key to understanding the sustainable soil functioning. The present work aims to examine the decomposition of HSs by filamentous dark-pigmented fungus Alternaria alternatа under the laboratory conditions and to determine the effect of easily assimilable organic carbon on this process. Analyzing such polydisperse substances like HSs by a complex integrated methodology makes it possible to explore the data on their decomposition by microorganisms.

Materials and methods

To achieve the aforementioned goals, we used chromatographic and spectroscopic approaches: low-pressure size-exclusion and hydrophobic interaction chromatography accompanied by absorption and fluorescence spectroscopy. To determine the effect cometabolism conditions produced on HS decomposition, two types of carbon substrates were added to the nutrient media: easily assimilable organic carbon (standard 0.3% or reduced 0.03% sucrose content) and hardly assimilable organic carbon (HSs), as well as their combinations. Five HS samples of different organic matter origin have been inspected: potassium humates (HPs) and humic acids (HAs) from coal, peat, and lignosulfonate. Correlation matrix and principal component analysis (PCA) were calculated for comprehensive data analysis.

Results and discussion

Transformations of the investigated HSs under fungal cultivation lead to the increase in the low molecular weight fraction, rise of hydrophilic fraction, enlargement of absorbance ratio A250/A365, shortening of the emission wavelength of the humic-type fluorescence, and growth in the fluorescence quantum yield measured with excitation at 355 nm. A positive correlation was observed between the accumulation of fungal biomass and the degree of HS decomposition. PCA analysis confirms that the difference in the results of HS decomposition largely depends on the sucrose content and the nature of HSs. We divided all the HS samples into four groups according to the degree of HS decomposition: original HS solutions, HPs altered using fungal cultivation at 0.03% sucrose, HAs after fungal cultivation at 0.03% sucrose, and finally, HSs (both HPs and HAs) after fungal cultivation at 0.3% sucrose.


In the laboratory experiments, we showed that (1) the isolated HAs were more effectively degraded than the parent HPs, and this process was more pronounced at a reduced sucrose content, and (2) the decomposition of stable organic compounds (HSs) was activated by the easily assimilable carbon sources (especially 0.3% sucrose) being present. We assume that it is the easily assimilable organic carbon that most likely triggers the HS degradation working as the priming effect in natural environments.


Absorption and fluorescence spectroscopy Decomposition of humic substances Easily assimilable organic carbon Filamentous fungi Hydrophobic interaction chromatography Size-exclusion chromatography 



Absorbance ratio at 250 nm and 365 nm


Chromophoric dissolved organic matter


Fulvic acids


Humic acid isolated from HPcoal


Humic acid isolated from HPpeat


Humic acids


Hydrophobic interaction chromatography


Potassium humates produced from coal


Potassium humates produced from lignosulfonate


Potassium humates produced from peat


Potassium humates


Humic substances


Low-pressure size-exclusion chromatography


Principal component analysis


Fluorescence quantum yield at 355 nm


Reversed-phase hydrophobic interaction chromatography


Funding information

The study was funded by the RFBR research project no. 18-016-00078.

Supplementary material

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ESM 1 (JPG 178 kb)
11368_2018_2209_MOESM2_ESM.docx (196 kb)
ESM 2 (DOCX 195 kb)


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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2018

Authors and Affiliations

  1. 1.Pirogov Russian National Research Medical UniversityMoscowRussia
  2. 2.Faculty of Soil ScienceLomonosov Moscow State UniversityMoscowRussia
  3. 3.Eurasian Center for Food SecurityLomonosov Moscow State UniversityMoscowRussia
  4. 4.Faculty of PhysicsLomonosov Moscow State UniversityMoscowRussia
  5. 5.Institute of Ecology and Evolution RASMoscowRussia

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