The stress response of tetracycline resistance genes and bacterial communities under the existence of microplastics in typical leachate biological treatment system.

Landfill leachate is an important source of microplastics (MPs) and antibiotic-resistance genes (ARGs). Here, in the presence of polystyrene MPs (PS-MPs) and polyethylene MPs (PE-MPs), the nitrogen and phosphorus removal effect and sludge structure performance were affected in an anaerobic-anoxic-aerobic system, a typical biological leachate treatment process. The abundance of tetracycline-resistance genes (tet genes) in biofilms on the two types of MP was significantly higher than that in the leachate and sludge, and the load on PE-MPs was higher than that on PS-MPs because of the porous structure of PE-MPs. Aging of the MPs increased their surface roughness and abundance of oxygen-containing functional groups and shaped the profile of ARGs in the MP biofilms. The biofilm biomass and growth rate on the two types of MP increased with the incubation time in the first 30 days, and was affected by environmental factors. Structural equation models and co-occurrence network analysis demonstrated that the MPs indirectly affected the spectrum of ARGs by affecting biofilm formation, and, to a lesser extent, had a direct impact on the selective enrichment of ARGs. We discuss the mechanisms of the relationships between MPs and ARGs in the leachate treatment system, which will have guiding significance for future research. Our data on the colonization of microorganisms and tet genes in MPs biofilms provide new evidence concerning the accumulation and transmission of these ARGs, and are important for understanding the mechanisms of MPs in spreading pollution.

Involvement of the Sch9/Rim15/Msn2 signaling pathway in the anti-aging activity of dendrobine from Dendrobium nobile Lindl. via modification of oxidative stress and autophagy.

BACKGROUND: Aging is an important pathogenic factor of age-related diseases and has brought huge health threat and economic burden to the society. Dendrobium nobile Lindl., a valuable herb in China, promotes longevity according to the record of ancient Chinese materia medica. This study aimed to discover the material basis of D. nobile as an anti-aging herb and elucidate its action mechanism. METHODS: K6001 yeast replicative lifespan assay was used to guide the isolation of D. nobile. The chronological lifespan assay of YOM36 yeast was further conducted to confirm the anti-aging activity of dendrobine. The mechanism in which dendrobine exerts anti-aging effect was determined by conducting anti-oxidative stress assay, quantitative real-time PCR, Western blot, measurements of anti-oxidant enzymes activities, determination of nuclear translocation of Rim15 and Msn2, and replicative lifespan assays of Δsod1, Δsod2, Δcat, Δgpx, Δatg2, Δatg32, and Δrim15 yeasts. RESULTS: Under the guidance of K6001 yeast replicative lifespan system, dendrobine with anti-aging effect was isolated from D. nobile. The replicative and chronological lifespans of yeast were extended upon dendrobine treatment. In the study of action mechanism, dendrobine improved the survival rate of yeast under oxidative stress, decreased the levels of reactive oxygen species and malondialdehyde, and enhanced the enzyme activities and gene expression of superoxide dismutase and catalase, but it failed to elongate the replicative lifespans of Δsod1, Δsod2, Δcat, and Δgpx yeast mutants. Meanwhile, dendrobine enhanced autophagy occurrence in yeast but had no effect on the replicative lifespans of Δatg2 and Δatg32 yeast mutants. Moreover, the inhibition of Sch9 phosphorylation and the promotion of nuclear translocation of Rim15 and Msn2 were observed after treatment with denrobine. However, the effect of dendrobine disappeared from the Δrim15 yeast mutant after lifespan extension, oxidative stress reduction, and autophagy enhancement. CONCLUSIONS: Dendrobine exerts anti-aging activity in yeast via the modification of oxidative stress and autophagy through the Sch9/Rim15/Msn2 signaling pathway. Our work provides a scientific basis for the exploitation of D. nobile as an anti-aging herb.