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Background: Macrolactins, a type of macrolide antibiotic, are toxic to the producer strains. As such, its level is usually maintained below the lethal concentration during the fermentation process. To improve the production of macrolactins, we applied adaptive laboratory evolution technology to engineer a saline-resistant mutant strain. The hypothesis that strains with saline resistance show improved macrolactins production was investigated. Results: Using saline stress as a selective pressure, we engineered a mutant strain with saline resistance coupled with enhanced macrolactins production within 60 days using a self-made device. As compared with the parental strain, the evolved strain produced macrolactins with 11.93% improvement in non-saline stress fermentation medium containing 50 g/L glucose, when the glucose concentration increased to 70 g/L, the evolved strain produced macrolactins with 71.04% improvement. RNA sequencing and metabolomics results revealed that amino acid metabolism was involved in the production of macrolactins in the evolved strain. Furthermore, genome sequencing of the evolved strain revealed a candidate mutation, hisDD41Y, that was causal for the improved MLNs production, it was 3.42 times higher than the control in the overexpression hisDD41Y strain. Results revealed that saline resistance protected the producer strain from feedback inhibition of end-product (macrolide antibiotic), resulting in enhanced MLNs production. Conclusions: In the present work, we successfully engineered a mutant strain with enhanced macrolactins production by adaptive laboratory evolution using saline stress as a selective pressure. Based on physiological, transcriptomic and genetic analysis, amino acid metabolism was found to benefit macrolactins production improvement. Our strategy might be applicable to improve the production of other kinds of macrolide antibiotics and other toxic compounds. The identification of the hisD mutation will allow for the deduction of metabolic engineering strategies in future research. [ABSTRACT FROM AUTHOR]

The Beibu Gulf harbors abundant underexplored marine microbial resources, which are rich in diversified secondary metabolites. The genera Vibrio is a well-known pathogenic bacterium of aquatic animals. In this study, 22 fungal strains were isolated and identified from the Beibu Gulf coral via the serial dilution method and internal transcribed spacer (ITS) sequence analysis, which were further divided into three branches by phylogenetic tree analysis. The crude extracts of them via small-scale fermentation were selected for the screening of inhibitory activity against Vibrio alginalyticus , Vibrio coralliilyticus , Vibrio harveyi , Vibrio parahaemolyticus , Vibrio owensii , and Vibrio shilonii. The results showed that eight fungal extracts displayed anti- Vibrio activity via the filter paper disk assay. Several of them showed strong inhibitory effects. Then, two tetramic acid alkaloids, equisetin (1) and 5′-epiequisetin (2), were identified from Fusarium equiseti BBG10 by bioassay-guided isolation, both of which inhibited the growth of Vibrio spp. with the MIC values of 86–132 μg/ml. The scanning electron microscope results showed that cell membranes of Vibrio became corrugated, distorted or ruptured after treatment with 1 and 2. Taken together, this study provided eight fungal isolates with anti- Vibrio potentials, and two alkaloid-type antibiotics were found with anti- Vibrio effects from the bioactive strain F. equiseti BBG10. Our findings highlight the importance of exploring promising microbes from the Beibu Gulf for the identification of anti- Vibrio for future antibiotic development. [ABSTRACT FROM AUTHOR]

[Display omitted] • Carbon-based adsorbents with intrinsic defects were designed and prepared. • SSG-C had high adsorption capacity, short equilibrium time and good reusability. • Intrinsic defects in the carbon-based adsorbents increased the adsorption. • The binding energies followed: ring defects of sp2 species > sp3 edge defects. • It is essential for intrinsic defects to activate π electrons on sp2 carbon. Due to their high adsorption capacity and low cost, carbon-based materials have experienced great progress in the removal of tetracyclines. Unfortunately, the nature of the adsorption site is far from clarified. Especially, it is still a great challenge to systematically explore the impact of intrinsic defects of carbon-based adsorbents on the adsorption of tetracyclines. Herein, carbon-based adsorbents with different defects were designed and prepared, and their adsorption properties of tetracyclines were systematically studied. From microscopic characterization of carbon-based adsorbents and batch adsorption experiments, the intrinsic defects of carbon-based adsorbents facilitated the adsorption performance of tetracyclines. The best adsorbent (SSG-C) had a very high adsorption capacity (526.9 mg/g for tetracycline (TTC); 360.9 mg/g for oxytetracycline (OTC)). Additionally, density functional theory simulation results show that the ring defects of sp2 species promoted the adsorption performance more than sp3 edge defects, and the adsorption performance increased with increasing ring defect of sp2 species. Based on the above analysis, we proposed that intrinsic carbon defects activate the π electrons of sp2 carbon and facilitate π-π interaction between carbon-based adsorbents and tetracyclines, particularly the ring defects of sp2 species. This study provides a decisive contribution to better understanding of the role of intrinsic defects in carbon-based adsorbents for removal of tetracyclines. [ABSTRACT FROM AUTHOR]

Microplastics (MPs), as vectors of pollutants, have attracted extensive attention because of their environmental effects. However, the adsorption behavior and antibiotic mechanism of environmentally exposed MPs is limited. Here, the adsorption of tetracycline (TC) onto virgin and soil-exposed polylactic acid (PLA), polyvinyl chloride (PVC) and polyethylene (PE) MPs showed that the adsorption capacity of MPs for TC increased after soil exposure, and PLA showed the strongest increase. Soil exposure increased the time to reach equilibrium, and the adsorption rate was controlled by both intraparticle diffusion and membrane diffusion. The isothermal adsorption results of soil-exposed PE and PLA indicated that TC adsorbed on heterogeneous surfaces was affected by the physicochemical adsorption process. The equilibrium absorption capacity of MPs for TC increased by 88% (PLA), 26% (PVC) and 15% (PE) after soil exposure. Soil dissolved organic matter promoted the desorption of TC from MPs, and TC speciation changed with pH. Soil-exposed MPs have the potential to promote TC degradation in solution without the addition of biological inhibitors. Moreover, density functional theory calculations verified that PE and PVC adsorbed TC through physical interactions, while hydrogen bonds were formed on PLA with TC. These results clarified the behavior and mechanisms of TC adsorption on virgin and soil-exposed MPs, which can help in the risk assessment of concomitant pollution of MPs and antibiotics. [Display omitted] • The adsorption of TC on PE and PVC was determined by the hydrophobicity. • Biofilm colonization on MPs surface increased the adsorption capacity of TC. • The soil DOM extraction facilitated the desorption of TC from MPs. • Soil-exposed MPs showed the potential to promote the degradation of TC. • The soil-exposed PLA promoted the formation of hydrogen bonds with TC. [ABSTRACT FROM AUTHOR]

Abstract: Two new aromatic butyrolactones, flavipesins A (1) and B (2), two new natural products (3 and 4), and a known phenyl dioxolanone (5) were isolated from marine-derived endophytic fungus Aspergillus flavipes. The structures of compounds 1–5 were elucidated by 1D- and 2D-NMR and MS analysis, the absolute configurations were assigned by optical rotation and CD data, and the stereochemistry of 1 was determined by X-ray crystallography analysis. 1 demonstrated lower MIC values against Staphylococcus aureus (8.0μg/mL) and Bacillus subtillis (0.25μg/mL). 1 also showed the unique antibiofilm activity of penetration through the biofilm matrix and kills live bacteria inside mature S. aureus biofilm. [Copyright &y& Elsevier]