Sub-iethal water disinfection may accelerate the spread of antibiotic resistance
Maximum Academic Press
The study reveals that environmental stressors do not merely kill bacteria; they can also prime surviving cells to take up resistance genes more efficiently, raising concerns about how antibiotic-resistant bacteria may spread in aquatic environments.
Antibiotic resistance genes and antibiotic-resistant bacteria are now recognized as emerging environmental contaminants, widely detected in rivers, lakes, wastewater, and even oceans. Aquatic systems provide ideal conditions for resistance genes to persist, interact, and spread among microorganisms. Bacteria exchange genetic material through horizontal gene transfer, including transformation, a process in which cells directly absorb free DNA from their surroundings. While transformation is known to contribute to resistance dissemination, its behavior under realistic environmental stress—such as incomplete disinfection—has remained poorly understood. Modern water treatment increasingly relies on advanced oxidation and light-based technologies, yet fluctuations in treatment efficiency can leave bacteria alive but stressed rather than fully inactivated. Understanding how these sub-lethal conditions influence ARG transfer is critical for public health protection.
A study (DOI:10.48130/biocontam-0025-0017) published in Biocontaminant on 08 December 2025 by Taicheng An’s team, Guangdong University of Technology, reveals that sub-lethal water disinfection can unintentionally accelerate the spread of antibiotic resistance by promoting stress-induced uptake of resistance genes in surviving bacteria.
Using a sub-lethal photocatalysis (sub-PC) system to simulate incomplete water disinfection, this study systematically evaluated how oxidative stress influences the transformation of ARGs. Two antibiotic-sensitive recipient strains, Escherichia coli DH5α and E. coli HB101, were exposed to sub-PC conditions and assessed for bacterial inactivation, physiological stress responses, and ARG uptake using a plasmid carrying the ampicillin resistance gene (amp). Under identical sub-PC exposure, bacterial abundances declined gradually by approximately 2 log after 120 min, yet nearly 10% of cells remained viable, providing a sufficient pool for horizontal gene transfer via transformation. Correspondingly, intracellular reactive oxygen species (ROS) levels increased markedly during the early phase (0–60 min), reaching three- to fourfold higher than baseline, while antioxidant enzymes catalase (CAT) and superoxide dismutase (SOD) were strongly induced, indicating activation of oxidative stress defenses. As treatment progressed, excessive damage led to declining ROS, CAT, and SOD levels, consistent with cell lysis and leakage. Following plasmid uptake, ampicillin-resistant transformants exhibited enhanced persistence under sub-PC, showing only a ~1 log reduction in abundance, supporting the notion that ARG acquisition improves stress tolerance. Optimization experiments revealed that transformation was most efficient at 37 °C and required high recipient densities; maximal transformant yields occurred at 10⁸–10⁹ CFU·mL⁻¹, with 10⁸ CFU·mL⁻¹ selected for robust quantification. Under these optimal conditions, transformation frequencies increased three- to four-and-a-half-fold, peaking at 50–60 min before declining as cellular damage accumulated. Mechanistic analyses showed that ROS scavengers significantly weakened, but did not abolish, the enhancement effect, confirming ROS as a key driver. Sub-PC also increased membrane permeability, elevated intracellular Ca²⁺ nearly fourfold, and depleted ATP, limiting Ca²⁺ efflux and reinforcing its accumulation. Gene expression profiling corroborated these trends, showing early upregulation of stress response, antioxidant, membrane transport, and DNA uptake genes, alongside repression of energy metabolism pathways.
The findings highlight a critical but underappreciated risk in water treatment systems: partially effective disinfection may promote, rather than prevent, the spread of antibiotic resistance. Sub-lethal stress not only allows bacteria to survive but actively enhances their capacity to acquire resistance genes from the environment. This mechanism could contribute to the persistence and amplification of antibiotic resistance in wastewater effluents, surface waters, and downstream ecosystems.
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References
DOI
Original Source URL
https://doi.org/10.48130/biocontam-0025-0017
Funding information
This work was supported by NSFC (42330702 and 42077333), and the Introduction Innovative and Research Teams Project of Guangdong Pearl River Talents Program (2023ZT10L102).
About Biocontaminant
Biocontaminant is a multidisciplinary platform dedicated to advancing fundamental and applied research on biological contaminants across diverse environments and systems. The journal serves as an innovative, efficient, and professional forum for global researchers to disseminate findings in this rapidly evolving field.
Method of Research
Experimental study
Subject of Research
Not applicable
Article Title
Enhanced transformation mechanisms of antibiotic resistance genes in water under the stress of sub-lethal photocatalysis
Viruses in wastewater: Silent drivers of pollution removal and antibiotic resistance
These findings suggest that current monitoring strategies, which rely heavily on bacterial indicators alone, may miss critical viral-driven risks and opportunities for safer wastewater reuse.
Viruses are among the most abundant biological entities in engineered water systems, including wastewater treatment plants (WWTPs). They interact intimately with microbial hosts, altering microbial metabolism, community structure, and ecological functions. In recent years, wastewater-based surveillance has gained attention for tracking pathogens and public health threats. However, most monitoring frameworks focus on a narrow set of bacterial indicators, such as Escherichia coli, while largely ignoring viruses and their complex interactions with pathogens. This gap limits our understanding of how viral communities respond to treatment processes and how they may influence health risks in reclaimed water systems. Based on these challenges, deeper investigation into virus–host dynamics across entire treatment processes is urgently needed.
A study (DOI:10.48130/biocontam-0025-0015) published in Biocontaminant on 04 December 2025 by Shu-Hong Gao’s team, Harbin Institute of Technology, reveals that persistent viral communities in wastewater treatment plants play a critical dual role in pollutant removal and antibiotic resistance dissemination, highlighting the urgent need to incorporate virus-based indicators and viral functional monitoring into wastewater treatment optimization and public health risk assessment.
Using a full-scale, process-wide metagenomic workflow, researchers analyzed 28 samples spanning influent-to-effluent units across three wastewater treatment configurations (AAO, AAO-MBR, and MBR), recovering 29,708, 14,138, and 13,961 high-quality viral contigs (≥5 kb) from the respective systems. These contigs were subjected to family-level taxonomic profiling, diversity and abundance analyses across treatment units and matrices (wastewater versus sludge), functional annotation of virus-encoded auxiliary metabolic genes (AMGs), and machine-learning–based virus–host prediction complemented by metagenome-assembled genomes (MAGs) and pathogen–virus co-occurrence networks. This integrated analysis identified 99 viral families across the full treatment continuum, with several taxa—most notably Peduoviridae and Casjensviridae—showing persistent, high prevalence from influent to effluent, demonstrating that viral populations are not confined to activated sludge but persist throughout treatment. Viral abundance and diversity were highest in AAO systems and in wastewater phases relative to sludge, while comparable Shannon diversity across plants and slightly elevated effluent diversity suggested convergent community assembly under shared treatment objectives. Community composition differed significantly among processes, with Gracegardnervirinae, Straboviridae, and Peduoviridae dominating AAO, AAO-MBR, and MBR, respectively, consistent with selective pressures imposed by treatment configurations. Importantly, viral dynamics did not mirror those of traditional indicators such as Escherichia coli, but instead closely tracked opportunistic pathogens Pseudomonas aeruginosa and Aeromonas caviae, supporting their potential as alternative indicators of virus-associated risk. Functional analyses revealed 117 AMGs across 12 metabolic pathways, enriched in wastewater and particularly active during biological treatment stages, implicating a “double-edged” role in enhancing carbohydrate, amino acid, and xenobiotic metabolism for pollutant removal while potentially facilitating the dissemination of antibiotic resistance genes via phage-mediated processes. Host prediction further identified Pseudomonadota as the predominant viral host phylum, enriched for multidrug-resistant pathogens, underscoring wastewater systems as hotspots of microbial evolution and highlighting the need for routine viral metagenomic monitoring and targeted process optimization to mitigate viral and antimicrobial-resistance risks in reclaimed water.
These findings have immediate implications for wastewater management and public health. They demonstrate that viruses should be integrated into routine biological monitoring frameworks, alongside bacteria, to better assess treatment performance and health risks. Identifying persistent viral–pathogen pairs offers new bioindicators for evaluating system efficiency and early warning signals for emerging threats. Moreover, understanding viral metabolic functions opens opportunities to harness beneficial viruses to enhance pollutant removal, while carefully managing the risks of resistance spread.
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References
DOI
Original Source URL
https://doi.org/10.48130/biocontam-0025-0015
Funding information
The study was financially supported by the National Natural Science Foundation of China (grants No. 52293443, 52321005, 52091545, and 52230004), the Natural Science Foundation of Guangdong Basic and Applied Basic Research Foundation (Grant No. 2024A1515010085), Shenzhen Science and Technology Program (Grant Nos GXWD20231127195344001 and JCYJ20241202123735045), and Shenzhen Overseas High-level Talents Research Startup Program (Grant No. 20200518750C).
About Biocontaminant
Biocontaminant is a multidisciplinary platform dedicated to advancing fundamental and applied research on biological contaminants across diverse environments and systems. The journal serves as an innovative, efficient, and professional forum for global researchers to disseminate findings in this rapidly evolving field.
Method of Research
Experimental study
Subject of Research
Not applicable
Article Title
Decoding pathogen-virus-metabolic gene networks in full-scale wastewater treatment: from virus diversity to hosts interaction
Rising temperatures reshape microbial carbon cycling during animal carcass decomposition in water
Maximum Academic Press
Using metagenomic sequencing across a realistic temperature gradient, researchers show that carcass decay triggers a surge in carbon-degradation genes, while warming selectively favors pathways that rapidly consume easily degradable carbon.
Animal death and decomposition are natural but powerful drivers of nutrient release. Each year, large quantities of animal carcasses enter terrestrial and aquatic ecosystems, releasing carbon-rich fluids that alter water chemistry and microbial activity. Aquatic systems are especially important, accounting for more than half of global primary production and playing a central role in carbon fixation and degradation. Microorganisms regulate these processes through specialized “carbon cycling genes.” While temperature is known to influence microbial metabolism, its combined effects with sudden carbon pulses—such as those from carcass decomposition—have remained poorly understood, particularly at the level of functional genes.
A study (DOI:10.48130/biocontam-0025-0012) published in Biocontaminant on 05 December 2025 by Huan Li’s team, Lanzhou University, highlights how climate warming and sudden carbon inputs can interact to redirect microbial carbon cycling, with implications for greenhouse gas emissions and aquatic ecosystem health.
Using a controlled carcass–water microcosm experiment across five temperature gradients (23–35 °C), this study employed metagenomic sequencing to comprehensively characterize microbial communities and functional genes involved in aquatic carbon cycling, while integrating multivariate statistics, network analysis, and pathway reconstruction to identify key drivers and mechanisms. The analysis showed that microorganisms carrying carbon-cycling genes spanned bacteria, eukaryotes, viruses, and archaea, but bacteria overwhelmingly dominated the system (mean 99.81%), with Proteobacteria, Actinobacteria, and Bacteroidetes as the most abundant groups. Temperature and carcass decomposition jointly reshaped microbial community structure, enriching Acidobacteria, Actinobacteria, Chloroflexi, Spirochaetes, and Firmicutes under warming alone, while favoring Verrucomicrobia, Proteobacteria, and genera such as Novosphingobium, Acidovorax, and Nocardioides during carcass decay. Functionally, carcass treatments produced a unimodal alpha-diversity pattern of carbon-cycling KEGG orthologs (KOs), peaking near 30 °C, and significantly altered beta diversity, with enrichment of carbon-degradation pathways including reductive TCA-related routes, gluconeogenesis, and the ethylmalonyl pathway. Carbohydrate-active enzyme (CAZy) profiles were dominated by glycosyltransferases, with key genes (e.g., GT2, GT4, CBM50, GH23, GT51) and hundreds of differential CAZy genes enriched in carcass conditions. Rising temperature strongly reduced carbon-cycling gene diversity in uncontaminated water, whereas this effect was buffered in carcass-contaminated systems by high nutrient availability. Approximately half of all carbon-cycling genes and over one-third of CAZy genes were temperature-sensitive, but substrate specificity diverged: warming promoted degradation of complex carbohydrates in controls, while only simple carbohydrate ester degradation increased with temperature during carcass decay, indicating preferential use of readily available carbon. Total carbon increased by nearly 87% following carcass decomposition and emerged as a key driver linking physicochemical conditions to functional gene structure. Network and pathway analyses further revealed a carcass-driven shift toward carbon degradation and fermentation, characterized by enhanced acetate and ethanol production and suppressed methane oxidation and parts of carbon fixation, demonstrating that carbon degradation, rather than fixation, dominates aquatic carbon cycling during carcass decomposition under warming conditions.
These findings have important implications for predicting carbon fluxes under climate change. As temperatures rise, aquatic environments experiencing sudden carbon inputs—such as mass fish deaths, livestock carcass disposal, or wildlife mortality events—may shift toward faster carbon turnover and increased release of carbon dioxide or other greenhouse gases. Understanding which microbial genes respond to warming helps refine models of carbon cycling and informs ecosystem management, particularly for freshwater bodies vulnerable to eutrophication and pollution.
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References
DOI
Original Source URL
https://doi.org/10.48130/biocontam-0025-0012
Funding information
This work was supported by the National Natural Science Foundation of China (32471575), Gansu Province Science and Technology Plan for Youth Science Fund (24JRRA458), and the Natural Science Foundation of Henan Province (222300420036).
About Biocontaminant
Biocontaminant is a multidisciplinary platform dedicated to advancing fundamental and applied research on biological contaminants across diverse environments and systems. The journal serves as an innovative, efficient, and professional forum for global researchers to disseminate findings in this rapidly evolving field.
Method of Research
Experimental study
Subject of Research
Not applicable
Article Title
Animal corpse decomposition under elevating temperature: a metabolic bridge from labile to recalcitrant carbon pools
Ushikuvirus: A newly discovered giant virus may offer clues to the origin of life
Ushikuvirus, an amoeba-infecting giant virus, joins the family of giant viruses that may have driven the evolution of complex cells
Tokyo University of Science
image:
Researchers discover a new virus called the “ushikuvirus” that provide evidence for the viral eukaryogenesis hypothesis and reveal virus–host interactions, shaping the evolution of eukaryotic cells.
view moreCredit: Professor Masaharu Takemura from Tokyo University of Science, Japan
The origin of life on Earth becomes even more fascinating and complex as we peer into the mysterious world of viruses. Said to have existed since living cells first appeared, these microscopic entities differ greatly from other forms of life. Composed of only genetic material, they lack the ability to synthesize proteins, which are essential for carrying out cellular activity and, ultimately, for life by itself.
As a result, scientists have long sought to unravel virus origins, how they evolve, and how they fit into the conventional tree of life. Professor Masaharu Takemura from the Graduate School of Science, Tokyo University of Science (TUS), Japan, has been at the forefront of this search. In 2001, he, along with Dr. Philip Bell, from the Department of Biological Sciences, Macquarie University, Sydney, independently proposed the cell nuclear virus origin theory, also known as viral eukaryogenesis (term coined by Dr. Bell). According to this hypothesis, the nucleus of eukaryotic cells (cells whose nucleus is bound by a membrane) originated from a large DNA virus such as poxvirus that infected an archaeal ancestor (single-celled microorganisms). Instead of killing the host, the virus set up a long-term presence inside the cytoplasm, and over time acquired essential genes from the host, and became what we now recognize as the nucleus of eukaryotic cells. This suggests that viruses may have played a foundational role in the emergence of life.
Nowadays, central to this idea are giant viruses that contain DNA, which were found in 2003. When they infect cells, they form specialized structures called virus factories inside the host. Some of these factories are enclosed within a membrane, much like a cell nucleus, where DNA replication takes place, hinting at an evolutionary connection between viruses and complex cells.
In recent years, new types of DNA viruses have been discovered, including members of the family Mamonoviridae, which infect acanthamoeba (a type of amoeba, which is a single-celled microorganism), and the closely related clandestinovirus, which infects vermamoeba (another type of amoeba from a different family).
Now, in a joint study published online in the Journal of Virology on November 24, 2025, Prof. Takemura along with researchers at the National Institute of Natural Sciences (NINS), Japan, report yet another of these giant DNA viruses that infect amoeba. Named ushikuvirus after Lake Ushiku in the Ibaraki Prefecture of Japan, where it was isolated. This discovery offers further support for the nuclear virus origin hypothesis.
The team included Mr. Jiwan Bae and Mrs. Narumi Hantori, Master’s degree students at the Graduate School of Science, TUS, along with Dr. Raymond Burton-Smith and Professor Kazuyoshi Murata from NINS.
“Giant viruses can be said to be a treasure trove whose world has yet to be fully understood. One of the future possibilities of this research is to provide humanity with a new view that connects the world of living organisms with the world of viruses,” says Prof. Takemura.
Giant viruses are ubiquitously present in the environment. However, their isolation remains a challenge. These viruses are highly diverse and the discovery of ushikuvirus is extremely valuable. The newly discovered ushikuvirus infects vermamoeba, like clandestinovirus, and is morphologically similar to members of the Mamonoviridae family, particularly Medusavirus, a genus characterized by its icosahedral shape and numerous short spikes on the capsid surface. However, ushikuvirus also shows distinct features: it induces a specific cytopathic effect that causes its vermamoeba hosts to grow into unusually large cells, and it possesses multiple spike structures with unique caps on the capsid surface, some with filamentous extensions, not seen in medusaviruses.
Additionally, unlike medusaviruses and clandestinovirus, which replicate within the intact host nucleus, ushikuvirus disrupts the nuclear membrane to produce viral particles. This suggests a phylogenetic link between Mamonoviridae family that utilizes intact nucleus as viral factory and giant viruses like pandoravirus that disrupt the nuclear membrane for replication. Researchers believe that these variations between viruses may have evolved as adaptations to their hosts.
By comparing these structural and functional differences, researchers are beginning to piece together how giant viruses have diversified over time and how their interactions with host cells may have shaped the evolution of complex eukaryotic life.
“The discovery of a new Mamonoviridae-related virus, ‘ushikuvirus,’ which has a different host, is expected to increase knowledge and stimulate discussion regarding the evolution and phylogeny of the Mamonoviridae family. As a result, it is believed that we will be able to get closer to the mysteries of the evolution of eukaryotic organisms and the mysteries of giant viruses,” says Prof. Takemura.
The discovery of these amoeba-infecting viruses could have practical implications for healthcare. Because certain Acanthamoeba species can cause diseases such as amoebic encephalitis, understanding how giant viruses infect and destroy amoebae may one day help scientists develop new strategies to prevent or treat such infections.
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Reference
DOI: 10.1128/jvi.01206-25
About The Tokyo University of Science
Tokyo University of Science (TUS) is a well-known and respected university, and the largest science-specialized private research university in Japan, with four campuses in central Tokyo and its suburbs and in Hokkaido. Established in 1881, the university has continually contributed to Japan's development in science through inculcating the love for science in researchers, technicians, and educators.
With a mission of “Creating science and technology for the harmonious development of nature, human beings, and society," TUS has undertaken a wide range of research from basic to applied science. TUS has embraced a multidisciplinary approach to research and undertaken intensive study in some of today's most vital fields. TUS is a meritocracy where the best in science is recognized and nurtured. It is the only private university in Japan that has produced a Nobel Prize winner and the only private university in Asia to produce Nobel Prize winners within the natural sciences field.
Website: https://www.tus.ac.jp/en/mediarelations/
About Professor Masaharu Takemura from Tokyo University of Science
Dr. Masaharu Takemura is a Professor in the Department of Mathematics and Science Education, Graduate School of Science at the Tokyo University of Science, Japan. His research interests include giant virus biology, viral eukaryogenesis, and virus education. Over his career, he has published more than 120 papers, amassing over 2,500 citations for his work. His research goal is to elucidate the evolution of giant viruses and eukaryotes and develop teaching materials for virus education.
Funding information
This research was supported by JSPS/KAKENHI grant number 20H03078 and Joint Research of the Exploratory Research Center on Life and Living Systems (ExCELLS) (ExCELLS program No, 22EXC601-4).
A joint research team discovered and characterized ushikuvirus, a new giant DNA virus that infects vermamoeba. This image (a) shows the 3D reconstruction of the virus, highlighting its spiked capsid (d). The finding further supports the nuclear virus origin hypothesis, which proposes that viruses played a role in the evolution of eukaryotic cells.
Credit
Professor Kazuyoshi Murata from the National Institute of Natural Sciences (NINS) Image source: https://journals.asm.org/doi/10.1128/jvi.01206-25
Professor Kazuyoshi Murata from the National Institute of Natural Sciences (NINS) Image source: https://journals.asm.org/doi/10.1128/jvi.01206-25
Journal
Journal of Virology
Method of Research
Experimental study
Subject of Research
Cells
Article Title
A newly isolated giant virus, ushikuvirus, is closely related to clandestinovirus and shows a unique capsid surface structure and host cell interactions
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