Cu(II)-Based Water-Dispersible Humic Acid: Synthesis, Characterizations, and Antifungal and Growth-Promoting Performances

Role of Humic Substances in the (Bio)Degradation of Synthetic Polymers under Environmental Conditions

Information on the detection of the presence and potential for degradation of synthetic polymers (SPs) under various environmental conditions is of increasing interest and concern to a wide range of specialists. At this stage, there is a need to understand the relationship between the main participants in the processes of (bio)degradation of SPs in various ecosystems (reservoirs with fresh and sea water, soils, etc.), namely the polymers themselves, the cells of microorganisms (MOs) participating in their degradation, and humic substances (HSs). HSs constitute a macrocomponent of natural non-living organic matter of aquatic and soil ecosystems, formed and transformed in the processes of mineralization of bio-organic substances in environmental conditions. Analysis of the main mechanisms of their influence on each other and the effects produced that accelerate or inhibit polymer degradation can create the basis for scientifically based approaches to the most effective solution to the problem of degradation of SPs, including in the form of microplastics. This review is aimed at comparing various aspects of interactions of SPs, MOs, and HSs in laboratory experiments (in vitro) and environmental investigations (in situ) aimed at the biodegradation of polymers, as well as pollutants (antibiotics and pesticides) that they absorb. Comparative calculations of the degradation velocity of different SPs in different environments are presented. A special place in the analysis is given to the elemental chemical composition of HSs, which are most successfully involved in the biodegradation of SPs. In addition, the role of photo-oxidation and photoaging of polymers under the influence of the ultraviolet spectrum of solar radiation under environmental conditions on the (bio)degradation of SPs in the presence of HSs is discussed.

Preparation, characterization, bacteriostatic efficacy, and mechanism of zinc/selenium-loaded sodium humate

In recent years, metal-based complexes including selenium (Se) and zinc (Zn)-containing compounds have been widely explored for their therapeutic properties due to their roles in biological processes and modulation of diverse molecular targets. Humic acid, as a metal complexing agent, is also widely used in biomedical field. In this work, three kinds of modified sodium humate (HNa), including Zn-HNA, Se-HNa, and Zn/Se-HNa, were prepared by ion exchange reaction method. The modified HNa was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and elemental mapping. The bacteriostatic activity and mechanism of modified HNa against gram-positive and gram-negative bacteria were investigated by testing bacterial inhibition zone, minimum inhibitory concentration, and capacity to destroy integrity of the bacterial membrane, promoting ROS generation level and prevention of biofilms. FTIR results showed that HNa could combine with zinc ions and selenite ions. The main XRD peaks did not change significantly. In the modified HNa, the particle shape was irregular. Compared to HNa, Zn-HNA, and Se-HNa, Zn/Se-HNa showed the strongest bacteriostatic activity. Zn/Se-HNa exhibited high bacteriostatic activity against gram-negative bacteria (Escherichia coli, Salmonella typhimurium, Klebsiella pneumoniae) and gram-positive bacteria (Staphylococcus aureus), but showed weak antibacterial activity against another gram-positive bacteria, Bacillus subtilis. The bacteriostasis was achieved by altering the permeability of bacterial cell membranes, generating ROS, and preventing the formation of biofilms. In conclusion, Zn/Se-HNa has high bacteriostatic activity, making it a suitable alternative to antibiotics in fields like the treatment of trauma infections and animal husbandry. KEY POINTS: • Preparate and characterize zinc- and selenium-loaded sodium humate (Zn/Se-HNa). • The combination of Zn and Se enhanced the bacteriostatic activity of HNa. • Zn/Se-HNa alters the permeability of bacterial cell membranes and promotes generation of ROS.

A Novel Guanine Elicitor Stimulates Immunity in Arabidopsis and Rice by Ethylene and Jasmonic Acid Signaling Pathways

Rice sheath blight (ShB) caused by Rhizoctonia solani is one of the most destructive diseases in rice. Fungicides are widely used to control ShB in agriculture. However, decades of excessive traditional fungicide use have led to environmental pollution and increased pathogen resistance. Generally, plant elicitors are regarded as environmentally friendly biological pesticides that enhance plant disease resistance by triggering plant immunity. Previously, we identified that the plant immune inducer ZhiNengCong (ZNC), a crude extract of the endophyte, has high activity and a strong ability to protect plants against pathogens. Here, we further found that guanine, which had a significant effect on inducing plant resistance to pathogens, might be an active component of ZNC. In our study, guanine activated bursts of reactive oxygen species, callose deposition and mitogen-activated protein kinase phosphorylation. Moreover, guanine-induced plant resistance to pathogens depends on ethylene and jasmonic acid but is independent of the salicylic acid signaling pathway. Most importantly, guanine functions as a new plant elicitor with broad-spectrum resistance to activate plant immunity, providing an efficient and environmentally friendly biological elicitor for bacterial and fungal disease biocontrol.

Synthesis, antibacterial evaluation, and safety assessment of CuS NPs against Pectobacterium carotovorum subsp. carotovorum

BACKGROUND

Copper agents have been widely used in crop protection because of their unique mechanism against resistant pathogenic bacteria; however, their application brings environmental pollution and biosafety problems. Therefore, environmentally friendly copper agents have attracted attention. In this study, copper sulfide nanoparticles (CuS NPs) were prepared, characterized, analyzed for antibacterial activity and safety.

RESULTS

Characterization results showed that the prepared pure CuS NPs have flake nanostructures, hexagonal crystal system, and size range from 40 to 60 nm. These CuS NPs exerted excellent antibacterial effects [median effective concentration (EC₅₀ ) = 17 mg L^-1 ] against Pectobacterium carotovorum subsp. carotovorum (Pcc) in vitro and can effectively delay and reduce bacterial infection in vivo. Antibacterial mechanism analysis revealed that CuS NPs can increase the levels of reactive oxygen species (ROS) and lipid peroxidation and destroy the structure of bacterial cells as observed through scanning electron microscopy (SEM) and Fourier-transform infrared (FTIR) spectroscopy. These NPs can also inhibit the motility of Pcc. At 7 and 14 days, the 50% lethal concentrations (LC₅₀ ) of CuS NPs against earthworms were 1136 and 783 mg kg^-1 , respectively, indicating their low acute toxicity to earthworms and environmental friendliness. Furthermore, the cells (L02) treated by CuS NPs showed relatively high cell viability (> 96%) and low apoptosis rate (only 5.2%), proving that CuS NPs had low cytotoxicity.

CONCLUSION

Compared with commercial dicopper chloride trihydroxide (Cu₂ (OH)₃ Cl), CuS NPs could be used as a highly effective, lowly toxic, and environmentally friendly antibacterial agent. © 2021 Society of Chemical Industry.