Physiological Responses of Methanosarcina barkeri under Ammonia Stress at the Molecular Level: The Unignorable Lipid Reprogramming

How denitrifiers defense ciprofloxacin: Insights from intracellular and extracellular stress response

Overuse of antibiotics has led to their existence in nitrogen-containing water. The impacts of antibiotics on bio-denitrification and the metabolic response of denitrifiers to antibiotics are unclear. We systematically analyzed the effect of ciprofloxacin (CIP) on bio-denitrification and found that 5 mg/L CIP greatly inhibited denitrification with a model denitrifier (Paracoccus denitrificans). Nitrate reduction decreased by 32.89 % and nitrous oxide emission increased by 75.53 %. The balance analysis of carbon and nitrogen metabolism during denitrification showed that CIP exposure blocked electron transfer and reduced the flow of substrate metabolism used for denitrification. Proteomics results showed that CIP exposure induced denitrifiers to use the pentose phosphate pathway more for substrate metabolism. This caused a substrate preference to generate NADPH to prevent cellular damage rather than NADH for denitrification. Notably, despite denitrifiers having antioxidant defenses, they could not completely prevent oxidative damage caused by CIP exposure. The effect of CIP exposure on denitrifiers after removal of extracellular polymeric substances (EPS) demonstrated that EPS around denitrifiers formed a barrier against CIP. Fluorescence and infrared spectroscopy revealed that the binding effect of proteins in EPS to CIP prevented damage. This study shows that denitrifiers resist antibiotic stress through different intracellular and extracellular defense strategies.

Comprehensive review of microbial production of medium-chain fatty acids from waste activated sludge and enhancement strategy

Microbial production of versatile applicability medium-chain fatty acids (MCFAs) (C6-C10) from waste activated sludge (WAS) provides a pioneering approach for wastewater treatment plants (WWTPs) to achieve carbon recovery. Mounting studies emerged endeavored to promote the MCFAs production from WAS while struggling with limited MCFAs production and selectivity. Herein, this review covers comprehensive introduction of the transformation process from WAS to MCFAs and elaborates the mechanisms for unsatisfactory MCFAs production. The enhancement strategies for biotransformation of WAS to MCFAs was presented. Especially, the robust performance of iron-based materials is highlighted. Furthermore, knowledge gaps are identified to outline future research directions. Recycling MCFAs from WAS presents a promising option for future WAS treatment, with iron-based materials emerging as a key regulatory strategy in advancing the application of WAS-to-MCFAs biotechnology. This review will advance the understanding of MCFAs recovery from WAS and promote sustainable resource management in WWTPs.

Phthalates Boost Natural Transformation of Extracellular Antibiotic Resistance Genes through Enhancing Bacterial Motility and DNA Environmental Persistence

The environmental dissemination of extracellular antibiotic resistance genes (eARGs) in wastewater and natural water bodies has aroused growing ecological concerns. The coexisting chemical pollutants in water are known to markedly affect the eARGs transfer behaviors of the environmental microbial community, but the detailed interactions and specific impacts remain elusive so far. Here, we revealed a concentration-dependent impact of dimethyl phthalate (DMP) and several other types of phthalate esters (common water pollutants released from plastics) on the natural transformation of eARGs. The DMP exposure at an environmentally relevant concentration (10 μg/L) resulted in a 4.8-times raised transformation frequency of Acinetobacter baylyi but severely suppressed the transformation at a high concentration (1000 μg/L). The promotion by low-concentration DMP was attributed to multiple mechanisms, including increased bacterial mobility and membrane permeability to facilitate eARGs uptake and improved resistance of the DMP-bounded eARGs (via noncovalent interaction) to enzymatic degradation (with suppressed DNase activity). Similar promoting effects of DMP on the eARGs transformation were also found in real wastewater and biofilm systems. In contrast, higher-concentration DMP suppressed the eARGs transformation by disrupting the DNA structure. Our findings highlight a potentially underestimated eARGs spreading in aquatic environments due to the impacts of coexisting chemical pollutants and deepen our understanding of the risks of biological-chemical combined pollution in wastewater and environmental water bodies.

Recovery capability of anaerobic digestion from ammonia stress: Metabolic activity, energy generation, and genome-centric metagenomics

Excessive ammonia stresses anaerobic digestion (AD) significantly. Although there has been progress in understanding AD under ammonia exposure, investigations on AD liberated from ammonia exposure are limited. Here, the recovery capability of AD from ammonia stress was evaluated, by examining specific methanogenic activity, energy-conserving capability, microbial community succession, and metabolic pathway reconstruction. The findings demonstrated that ammonia stress relief resulted in < 50% methane recovery, with propionate conversion identified as the critical impediment to AD reactivation. Energy generation could not recovered either. Efforts to mitigate ammonia stress failed to restore acetoclastic methanogens, e.g., Methanothrix soehngenii, and proved futile in awakening propionate oxidizers, e.g., Desulfobulbus. Interestingly, a symbiotic metabolism emerged, prevailing in stress-relieved AD due to its energy-conserving advantage. This study underscores the importance of targeted interventions, including stimulating acetoclastic methanogenesis, propionate oxidation, and energy generation, as priorities for AD recovery following ammonia stress, rather than focusing solely on ammonia level management.

Microbiome-functionality in anaerobic digesters: A critical review

Microbially driven anaerobic digestion (AD) processes are of immense interest due to their role in the biovalorization of biowastes into renewable energy resources. The function-versatile microbiome, interspecies syntrophic interactions, and trophic-level metabolic pathways are important microbial components of AD. However, the lack of a comprehensive understanding of the process hampers efforts to improve AD efficiency. This study presents a holistic review of research on the microbial and metabolic "black box" of AD processes. Recent research on microbiology, functional traits, and metabolic pathways in AD, as well as the responses of functional microbiota and metabolic capabilities to optimization strategies are reviewed. The diverse ecophysiological traits and cooperation/competition interactions of the functional guilds and the biomanipulation of microbial ecology to generate valuable products other than methane during AD are outlined. The results show that AD communities prioritize cooperation to improve functional redundancy, and the dominance of specific microbes can be explained by thermodynamics, resource allocation models, and metabolic division of labor during cross-feeding. In addition, the multi-omics approaches used to decipher the ecological principles of AD consortia are summarized in detail. Lastly, future microbial research and engineering applications of AD are proposed. This review presents an in-depth understanding of microbiome-functionality mechanisms of AD and provides critical guidance for the directional and efficient bioconversion of biowastes into methane and other valuable products.

Near-Native Imaging of Label-Free Silver Nanoparticles-Triggered 3D Subcellular Ultrastructural Reorganization in Microalgae

Understanding the spatial orientation of nanoparticles and the corresponding subcellular architecture events favors uncovering fundamental toxic mechanisms and predicting response pathways of organisms toward environmental stressors. Herein, we map the spatial location of label-free citrate-coated Ag nanoparticles (Cit-AgNPs) and the corresponding subcellular reorganization in microalgae by a noninvasive 3D imaging approach, cryo-soft X-ray tomography (cryo-SXT). Cryo-SXT near-natively displays the 3D maps of Cit-AgNPs presenting in rarely identified sites, namely, extracellular polymeric substances (EPS) and the cytoplasm. By comparative 3D morphological assay, we observe that Cit-AgNPs disrupt the cellular ultrastructural homeostasis, triggering a severe malformation of cytoplasmic organelles with energy-producing and stress-regulating functions. AgNPs exposure causes evident disruption of the chloroplast membrane, significant attenuation of the pyrenoid matrix and starch sheath, extreme swelling of starch granules and lipid droplets, and shrinkage of the nucleolus. In accompaniment, the number and volume occupancy of starch granules are significantly increased. Meanwhile, the spatial topology of starch granules extends from the chloroplast to the cytoplasm with a dispersed distribution. Linking the dynamics of the internal structure and the alteration of physiological properties, we derive a comprehensive cytotoxic and response pathway of microalgae exposed to AgNPs. This work provides a perspective for assessing the toxicity at subcellular scales to achieve label-free nanoparticle-caused ultrastructure remodeling of phytoplankton.

IR-based device to acquire real-time online heart ECG signals of fish (Cyprinus carpio) to evaluate the water quality

Water quality monitoring is a challenging task due to continuous pollution. The rapid development of engineering technologies has paved the way for the development of efficient and convenient computer-based online continuous water-quality assessment techniques. Techniques based on biological-responses are gaining attention, worldwide. Different biosensors have been developed in recent years to monitor real-time biological responses to evaluate water-quality. The survival and function of various organs of the organism depends on the cardiac system. Alterations in the cardiac system could signify the occurrence/initiation of stress in the organism. We developed a real-time online cardiac function assessment system-OCFAS to acquire fish ECG-signals. We obtained P-wave, R-wave, T-wave, PR-intervals, QT-intervals and QRS-complex continuously, which did not affect the normal activities of carp. We exposed Cyprinus carpio to different concentrations (National Environmental Quality Standards) of ammonia for 48 h. Our OCFAS has precisely acquired the required ECG-signals. A real-time dataset reveals sensitivity to ammonia in carp ECG-indexes. Compared with the control group the P-wave, R-wave and T-wave were weaker in ammonia-treated groups. In contrast, the PR-intervals, QT-intervals and QRS-complex were prolonged in the ammonia-treatment groups. The self-organizing map signifies that the PR-intervals, the QRS-complex and the QT-intervals are consistent with environmental stress. Linear regression analysis also quantitatively signifies that the PR interval has the highest R2 value and the lowest SSE-value, followed by the QRS complex and the QT interval. A concentration-related effect was observed in the ammonia treated groups. The integrated biomarker response (IBRv2) index was used to determine the overall stress of ammonia on carp heart ECG-indexes. IBRv2 also supports the real-time response of carp to ammonia stress. Ammonia levels in the aquaculture and water environment require special attention to avoid its adverse effects on the health of aquatic biota. Our study emphasizes the importance of online real-time fish ECG for water-quality assessment.