Estimation of Uptake of Humic Substances from Different Sources by Escherichia coli Cells under Optimum and Salt Stress Conditions by Use of Tritium-Labeled Humic Materials

Abstract

The primary goal of this paper is to demonstrate potential strengths of the use of tritium-labeled humic substances (HS) to quantify their interaction with living cells under various conditions. A novel approach was taken to study the interaction between a model microorganism and the labeled humic material. The bacterium Escherichia coli was used as a model microorganism. Salt stress was used to study interactions of HS with living cells under nonoptimum conditions. Six tritium-labeled samples of HS originating from coal, peat, and soil were examined. To quantify their interaction with E. coli cells, bioconcentration factors (BCF) were calculated and the amount of HS that penetrated into the cell interior was determined, and the liquid scintillation counting technique was used as well. The BCF values under optimum conditions varied from 0.9 to 13.1 liters kg ؊1 of cell biomass, whereas under salt stress conditions the range of corresponding values increased substantially and accounted for 0.2 to 130 liters kg ؊1 . The measured amounts of HS that penetrated into the cells were 23 to 167 mg and 25 to 465 mg HS per kg of cell biomass under optimum and salt stress conditions, respectively. This finding indicated increased penetration of HS into E. coli cells under salt stress.Humic substances (HS) are natural organic compounds comprising 50 to 90% of the organic matter of peat, coal, and sapropel (i.e., sludge that accumulates at the bottom of lakes), as well as of the nonliving organic matter of soil and water ecosystems (9,34,53). Being the products of stochastic synthesis, HS are characterized as polydispersed substances having elemental compositions that are nonstoichiometric and structures which are irregular and heterogeneous. Thus, it is not possible to assign an exact structure to HS. Instead, they are operationally defined using a model structure predicated on available compositional, structural, functional, and behavioral data: a model structure containing all the same basic structural units and types of reactive functional groups (46). HS have been demonstrated to contain a large amount of residues resembling the original building blocks (aromatic subunits, amino acids, carbohydrates, etc.) (51) as well as polyphenolic components with nonhydrolyzable C-C and ether bonds (51, 16). Since humic matter is a complex mixture of organic substances, HS yield extremely high polydispersity values (i.e., the ratio of weight-average molecular weight to the number-average molecular weight [M w /M n ]), which vary within the range of 1.64 to 4.40 (38). These extremely high polydispersity values mean that even though they yield relatively high values of molecular weight, HS contain a low-molecular-weight fraction.HS are known to play important roles in protecting microorganisms and higher plants from climatic and technogenic stresses, such as pollution, draught, UV irradiation, and pathogen and viral infections (2, 22, 31). However, mechanisms underlying protective functions of these natural systems are still poorly und...

Tritium label in studying sorption of humic substances by carbon-based nanomaterials

“…One can see that for all tested nanomaterials under the same equilibrium concentration sorption of CHA-Pow was higher than FA,SR. The same result was previously obtained for adsorption at aqueous/organic liquid interfaces [18,19].…”

“…[19]. According to these scales CHA-Pow is more hydrophobic and [16,18,19]. We compared the results obtained for SWNT and graphene with arenes because of similarities of hybridization state of carbon atoms in these molecules.…”

“…With the help of liquid scintillation spectrometry of tritium and 3 H-HS with equal distribution of label among HS components hydrophobicity and surface activity scales were obtained and described in Ref. [19]. According to these scales CHA-Pow is more hydrophobic and [16,18,19].…”

“…Since tritium thermal activation technique is based on the bombardment of solid organic target with tritium atoms that are forms by thermal dissociation of tritium molecules on Wwire the method allows introduction of 3 H-label in any structural fragment of macromolecule, regardless of its nearest surrounding and HS origin. 3 H-HS obtained by tritium thermal activation method were successfully used for studying their adsorption and distribution in aqueous/organic liquid systems [18,19] and their interaction with bacteria and plants [19].…”

Combined Effects of Silver Nanoparticles and Humic and Fulvic Acids on Vibrio splendidus Growth

“…This sorption may affect structure, fluidity and permeability of bacterial cell membranes. 26 In addition, humic substances could be internalized by bacterial cell 27 and used as carbon source. 18 As a consequence, the HA/FA ratio in surface waters could dictate the toxic outcome of AgNPs.…”