Photochemical Behavior of Microbial Extracellular Polymeric Substances in the Aquatic Environment

Abstract

Microbially derived extracellular polymeric substances (EPSs) occupy a large portion of dissolved organic matter (DOM) in surface waters, but the understanding of the photochemical behaviors of EPS is still very limited. In this study, the photochemical characteristics of EPS from different microbial sources (Shewanella oneidensis, Escherichia coli, and sewage sludge flocs) were investigated in terms of the production of reactive species (RS), such as triplet intermediates (3EPS*), hydroxyl radicals (•OH), and singlet oxygen (1O2). The steady-state concentrations of •OH, 3EPS*, and 1O2 varied in the ranges of 2.55–8.73 × 10–17, 3.01–4.56 × 10–15, and 2.08–2.66 × 10–13 M, respectively, which were within the range reported for DOM from other sources. The steady-state concentrations of RS varied among different EPS isolates due to the diversity of their composition. A strong photochemical degradation of the protein-like components in EPS isolates was identified by excitation emission matrix fluorescence with parallel factor analysis, but relatively, humic-like components remained stable. Fourier-transform ion cyclotron resonance mass spectrometry further revealed that the aliphatic portion of EPS was resistant to irradiation, while other portions with lower H/C ratios and higher O/C ratios were more susceptible to photolysis, leading to the phototransformation of EPS to higher saturation and lower aromaticity. With the phototransformation of EPS, the RS derived from EPS could effectively promote the degradation of antibiotic tetracycline. The findings of this study provide new insights into the photoinduced self-evolution of EPS and the interrelated photochemical fate of contaminants in the aquatic environment.

Photo-Reactivity and Photo-Transformation of Algal Dissolved Organic Matter Unraveled by Optical Spectroscopy and High-Resolution Mass Spectrometry Analysis

“…Compared with I6, the O/C wa , AImod wa and DBE wa values of I1 were much lower (Table ), suggesting that lower molecular weight was more saturated and less aromatic, which is consistent with the results of SUVA 254 and FI. H/C wa of both two fractions slightly increased and DBE wa decreased, indicating that the unsaturated components in IOM fractions were more sensitive to light radiation and prone to photo-transformation to more saturated substances. , The aromatic component in I1 was more prone to photo-transformation compared to I6, with a greater reduction in AImod wa . Noticeably, the O/C wa of I1 increased which was probably due to the rising carbohydrates and tannins (Figure a).…”

“…H/C wa of both two fractions slightly increased and DBE wa decreased, indicating that the unsaturated components in IOM fractions were more sensitive to light radiation and prone to phototransformation to more saturated substances. 71,72 The aromatic component in I1 was more prone to photo-transformation compared to I6, 72 with a greater reduction in AImod wa . Noticeably, the O/C wa of I1 increased which was probably due to the rising carbohydrates and tannins (Figure 5a).…”

“…They were dominated by Ncontaining compounds (Figure 5d) with a higher proportion of decomposed than produced, showing a slight decrease in the total number of molecules (Figure S9), which might be mineralized directly into inorganic carbon forms. 3 These substances containing a large portion of unsaturated structures that are more sensitive to light and react preferentially during light radiation, 71 with the N-containing compounds (CHON and CHONS) being particularly photo-unstable. 72 For the IOM fraction with lower MW, the content of concentrated aromatic hydrocarbons increased in region ⑤ (Figure 5e), and the molecular abundance increased in the high O/C region (regions ④ and ⑥), indicating that polymerization probably occurred during light radiation.…”

Contrasting Impacts of Photochemical and Microbial Processing on the Photoreactivity of Dissolved Organic Matter in an Adirondack Lake Watershed

“… 128 Together with the patterns observed with leaf and soil Oa DOM, results from the glucose incubation experiment consolidated the findings in the literature with respect to the enhanced photoreactivity conferred by microbially derived DOM such as wastewater effluent organic matter 129 − 132 and extracellular polymeric substances released by heterotrophic bacteria. 133 …”

Dissolved Organic Matter Acting as a Microbial Photosensitizer Drives Photoelectrotrophic Denitrification

“…DOM is a complicated mixture of compounds and contains a large amount of photoactive functional groups (e.g., aromatic groups). − The concentration of DOM in surface water is in the range of one to several hundred mgC/L. , Upon irradiation, DOM is capable of generating oxidative (e.g., reactive oxygen species (ROS)) and reductive species (e.g., hydrated electrons). In previous studies, most attention has been given to the photooxidation reactions of DOM to mediate the conversion of environmental pollutants, including organic pollutants, resistance genes, heavy metals, etc. − For example, photoirradiation with DOM enhanced the oxidative degradation of extracellular antibiotic resistance genes .…”