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Dissolved humic substances and fungal metabolites can exhibit similar fluorescence properties

Fedoseeva Elena, Patsaeva Svetlana, Khundzhua Daria, Prudnikova Eva, Terekhova Vera

Abstract

The fluorescence spectroscopy is commonly used to characterize humic substances, the main components of natural organic matter (NOM). It can be used as well to discriminate microbial cells and biochemical processes. The fluorescence properties of molecules can be described by such parameters as dependence of emission wavelength λem on excitation wavelength λex, and the value of fluorescence quantum yield (number of fluorescent photons per photons absorbed). The release of colored dissolved organic matter (CDOM) by different groups of microorganisms was studied earlier. This study was aimed to assess fluorescence properties of fungal cultural liquids and to reveal their similarity with fluorescence properties of aquatic CDOM and one of humic products. We investigated fluorescence properties of cultural liquids of four fungal strains Alternaria alternatа, Cladosporium cladosporioides, Trichoderma harzianum, and Fusarium solani and compared them with fluorescence properties of humic product (humic acid from coal) and CDOM. Fluorescence spectra were measured using a luminescence spectrometer Solar CM2203 at wavelengths of the exciting radiation ranging from 250 to 500 nm. We showed that cultured filamentous fungi release fluorescent CDOM like typical fluorescent fluorescent CDOM in aquatic ecosystems and in humic product. Fluorescent CDOM released from some fungal cultures also showed comparable apparent fluorescent quantum yields, blue shift of emission spectra, and a very close match of ultraviolet–visible absorbance. Given the importance of filamentous fungi in the global carbon cycle our results indicate that filamentous fungi are likely to be important sources of aquatic and soil fluorescent CDOM. This work was supported by the Russian Foundation for Basic Research (grants number 18-04-01218 and 19-05-00056) and the Ministry of Science and Higher Education of the Russian Federation.

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Fedoseeva Elena
Pirogov Medical University
Russia

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