JHM Column Chongqing University Li Hong's team: Microplastics promote bacterial colonization and induce algal toxin degradation

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First author: He Yixin Corresponding author: Li Hong, Mao Yufeng Li Hong's research team and Associate Professor Mao Yufeng from the Hohai College of Chongqing Jiaotong University published a research paper entitled "Microplastics benefit bacteria colonization and induce microcystin degradation" in the Journal of Hazardous Materials, a well-known academic journal in the environmental field
.

This study focused on the potential impact of widely distributed microplastics in the water environment on the environmental migration behavior of microcystins, simulated the turbulent hydraulic conditions of the Three Gorges Reservoir area under laboratory conditions, and observed the formation process of biofilms on the surface of microplastics and its physical/biosorption and degradation processes for microcystins
.

The results showed that microplastics could not only adsorb algal toxins, but also act as carriers for algal toxin-degrading bacteria and promote the biosorption and degradation of microcystins
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This project provides new theoretical underpinnings for understanding the dual roles that microplastics play in aquatic ecosystems (both pollutants and degradation agents of other pollutants)
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Full article Quick Fact Microplastics (MPs) can act as ideal carriers for biofilms while adsorbing pollutants in aqueous environments
.

However, the interaction process between the toxic substances adsorbed by MPs and the biofilms formed on their surfaces is still unclear
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In this study, a 37-day indoor simulation experiment was conducted to investigate the effect of polystyrene microplastics (PS-MPs) on the environmental behavior of microcystins (MC-LR) in turbulent water bodies
.

The results indicated that the adsorption of PS-MPs was the main process leading to the rapid decrease of MC-LR concentration in water, and the attached biofilm changed the surface properties of PS-MPs and enhanced the MC with the colonization of PS-MPs by microorganisms.
- Biosorption of LR
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Meanwhile, microcystin-degrading bacteria, such as Sphingomonadaceae and Methylophilaceae, can colonize and grow in the surface biofilm of PS-MPs and promote the biodegradation process of MC-LR, Eventually, the concentration of MC-LR in water decreased continuously, and the maximum removal rate reached 35.
8% in the PS-MPs addition group, and the interaction between PS-MPs, biofilms and MC-LR may be ubiquitous in natural water bodies
.

INTRODUCTION Microplastics (MPs) widely distributed in the environment easily become carriers of various pollutants due to their large specific surface area and hydrophobicity
.

It has been shown that MPs can adsorb various pollutants (such as antibiotics and fungicides) and affect their environmental behavior
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In addition, pollutants adsorbed by MPs can be ingested by aquatic organisms, leading to the migration and bioaccumulation of toxic substances along the network, and further increasing the ecological risk of these pollutants
.

Therefore, a deep understanding of the interactions between MPs and pollutants is crucial for understanding and predicting the ecological risks of MPs
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Microcystins (MCs) are toxic secondary metabolites produced by cyanobacteria that can pose a threat to animal and human health, and MC-LR is one of the most widely distributed isomers of MCs
.

Previous studies have shown that MCs can enter the food web by adsorbing on MPs
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Turbulence is a ubiquitous hydrodynamic feature in the natural water environment and can also affect the environmental behavior of pollutants
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Previous studies by this research team have shown that increasing the water flow rate can promote the adsorption of toxic pollutants on suspended particulate matter, thereby reducing the concentration of toxic pollutants in the water phase
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In addition, turbulence may also affect the formation process of biofilms and the composition of biological communities on the membranes, but the interaction process between MPs covered by biofilms and other pollutants in turbulent water bodies is still lacking
.

In this study, indoor simulation experiments were carried out in the Approximately Homogeneous Turbulence Simulation (AHTS) system to study the interaction of MPs, microorganisms and MC-LR in tributary water samples of the Three Gorges Reservoir area under turbulent conditions.
The purpose is to (1) reveal the dynamic changes of MC-LR concentration in turbulent water bodies containing PS-MPs; (2) observe the formation process of biofilm on the surface of PS-MPs; (3) clarify the effect of biofilm on PS-MPs and MC-LR Effects in LR interactions
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Figure 1: Schematic diagram of the treatment group in this study
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a is a schematic diagram of the composition of AHTS, and b is five experimental treatment groups
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Figure 2: Dynamic changes of MC-LR concentrations in different treatment groups
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During the experimental period of 37 d, the MC-LR concentration in the group without PS-MPs but with NaN3 addition (shielded from microbial effects, AHTS I, control) showed a slight decrease (3.
3%), which may be caused by MC-LR photolysis caused
.

The MC-LR concentration in AHTS III shielded from microbial influence with NaN3 showed a significant decrease on day 2, and then the MC-LR level decreased insignificantly in subsequent run times
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On the contrary, in AHTS IV, AHTS II and AHTS V, the concentration of MC-LR continued to decrease and was relatively stable until the 25th day
.

On the 37th day, the removal rates of MC-LR in AHTS IV, AHTS II, AHTS V and AHTS III were 35.
8%, 28.
2%, 24.
9% and 12.
6%, respectively
.

The structure of the biofilm on the surface of PS-MPs at the 37th d was studied by confocal microscopy (as shown in Fig.
3)
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Fluorescence in different colors indicated the different components present in the biofilm, with green representing live bacteria, while red and blue represented dead bacteria and polysaccharides, respectively, all three of which were the main components of biofilms on the surface of PS-MPs
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When the experiment was carried out on the 37th day, no live dead bacteria and exopolysaccharides were observed on the surface of PS-MPs of AHTS III, which indicated that the NaN3 added at the beginning of the experiment achieved a good bacteriostatic effect, while in AHTS IV The surface of PS-MPs has obvious microbial membrane composed of living cells (green), dead cells (red) and exopolysaccharides (blue), and the distribution of PS-MPs in AHTS V is more significant
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The proportion of live bacteria in the composition of biofilms on the surface of these two groups of microorganisms was significantly larger than that of dead bacteria, and both had obvious adhesion of extracellular polysaccharides
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Figure 3: Confocal laser images of PS-MPs samples in AHTS III, AHTS IV, and AHTS V on the 37th day
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At the end of the experiment, the bacteria on the surface of PS-MPs in AHTS IV were classified as Pirellulaceae, Comamonadaceae (Commonadaceae), Beijerinckiaceae (Bayerinckiaceae), Methylophilaceae (Methylophilus), Hyphomonadaceae (Hyphomonadaceae).
bacteria), accounting for 7.
8%, 6.
9%, 6.
5%, 5.
7%, and 5.
8%, respectively.
The dominant species of bacteria on the surface of PS-MPs in AHTS IV were Lachnospiracea (Lachnospiracea) and Moraxellaceae (Moraxellaceae).
), Prevollaceae, and Ruminococcaceae (Ruminococcaceae) with relative abundances of 13.
6%, 10.
1%, 11.
4%, and 5.
6% (Fig.
4)
.

In addition, important MCs-degrading bacteria Sphingomonadaceae (Sphingomonas) and Methylophilaceae (Methylophilaceae) appeared in the PS-MPs surface biofilms in AHTS IV and AHTS V, thus making the surface biofilms of MPs possible.
It has the ability to degrade MCs simultaneously
.

Figure 4: Histogram of bacterial abundance on the surface of PS-MPs in AHTS IV and AHTS V at 37 d
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The analysis of the degradation products of MC-LR showed that (Fig.
5), compared with the initial, the ion peak intensity of MC-LR in the control group did not change significantly, and the ion peak intensity of MC-LR in AHTS III decreased slightly, but The typical degradation products of MC-LR were not observed in both groups, indicating that the biodegradation process of MC-LR did not occur in the two groups added with NaN3 during the experiment
.

A new ion peak appeared at 331.
2 in the m/z spectra of AHTS Ⅱ, AHTS Ⅳ and AHTS Ⅴ, whose ionic composition is C9H29O6N7, which is the typical degradation product of MC-LR Adda ion fragment, which proves that the three groups of treatments have a new ion peak at 331.
2.
Different degrees of biodegradation occurred in the MC-LR experiment.
Among them, the ionic strength of MC-LR degradation products in AHTS IV was the strongest, and the concentration of MC-LR decreased most obviously, compared with MC-LR in AHTS II and AHTS V.
The decrease of the LR peak is smaller
.

Figure 5: MC-LR spectral analysis and product identification by LC/MS before and after the experiment: (a) (b) indicate AHTS I (c) (d) indicate AHTS II, (e) (f) indicate AHTS III, (g) (h) represents AHTS IV, and (i) (j) represents AHTS V
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Summary In this paper, the effects of PS-MPs and their surface biofilms on the migration and biodegradation of MC-LRs in turbulent water were investigated
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The results showed that PS-MPs had a strong physical adsorption capacity for MC-LR, and the surface properties of PS-MPs changed with the formation of biofilm on the surface of PS-MPs, which triggered the biosorption of MC-LR
.

In addition, algal toxin-degrading bacteria were detected in the PS-MPs surface biofilm, which promoted the MC-LR biodegradation process on the membrane
.

Therefore, physical adsorption, biosorption and biodegradation significantly reduced the MC-LR content in water, and these combined effects were more pronounced in turbulent water bodies than in still water
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This study revealed the dual roles of MPs as pollutant carriers and pollutant degradation mediators in turbulent water environments, and provided new perspectives and arguments for understanding and evaluating the composite eco-environmental effects of MPs and pollutants
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About the author The first author: He Yixin, a master student at the School of Environment and Ecology, Chongqing University
.

His main research interests are cyanobacterial physiology and environmental toxicology of micro-nano plastics
.

A total of 11 SIC papers have been published, including 5 SCI papers as the first author and co-first author
.

Email: yixinhe@cqu.
edu.
cn Corresponding author: Li Hong, Ph.
D.
, associate professor and doctoral supervisor of School of Environment and Ecology, Chongqing University
.

The research direction is environmental ecology and ecological restoration of polluted environment.
He presided over more than ten projects of the National Natural Science Foundation of China Youth Fund, general projects, and general projects of China Postdoctoral Science Foundation.
6 provincial and ministerial projects
.

Published 51 papers so far, including 23 research papers published in important journals in the field of environmental science/ecology as the first author or corresponding author (including co-correspondence), including 1 highly cited paper, and authorized the invention as the first author He has 1 patent, won the second prize of Science and Technology Progress Award of the Ministry of Education in 2012, and won the first prize of Chongqing Science and Technology Progress Award in 2020
.

Email: hongli@cqu.
edu.
cn Corresponding author: Mao Yufeng, Ph.
D.
, associate professor and master tutor of Hohai College of Chongqing Jiaotong University
.

Mainly engaged in the research work on the environmental behavior, ecological risks of new pollutants, and phytoplankton physiology and ecology
.

He presided over a number of national, provincial and ministerial-level projects such as the National Natural Science Foundation of China and the Natural Science Foundation of Chongqing Municipality
.

Two papers were selected as ESI Hotspot/Highly Cited
.

Won the first prize of Huaxia Construction Science and Technology Progress Award
.

Email: maoyufeng@cqjtu.
edu.
cn JHM family journals include Journal of Hazardous Materials (JHM), Journal of Hazardous Materials Letters (JHM Letters), and Journal of Hazardous Materials Advances (JHMA)
.

The three journals share the same scope, focusing on the migration, impact, detection, and removal of environmentally hazardous substances
.

The flagship journal JHM publishes high-level scientific research and review articles, JHM Letters is completely open access, and publishes Letter-type scientific research and cutting-edge review articles (3000 words limit, 4 figures/tables), and JHMA is positioned as a mid-range open access journal
.

Source: JHM Family
.

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