Tan Lin-Rui,Xia Peng-Fei,Zeng Raymond J.,Li Qian,Sun Xue-Fei,Wang Shu-Guang
The interactions between antibiotics and microorganisms have attracted enormous research attentions. In this study, we investigated the effects of two typical aminoglycoside antibiotics on the aggregation of the model cyanobacterium, Synechococcus elongatus , and the dominating strain in algal blooms, Microcystis aeruginosa , via the analysis of zeta potentials, hydrophobicity, and extracellular polymeric substances (EPS) secretion . The results showed that low-level antibiotics promoted the aggregation of S. elongatus and M. aeruginosa by 40 and 18% under 0.10 and 0.02 μg/mL of kanamycin, respectively, which was mainly attributed to the combined effects of increased zeta potentials and the ratio between extracellular proteins and polysaccharides. Tobramycin exerted similar effects. Additionally, we discovered that at low pH (pH 5) and ionic strength (1 mM Na + and 2 mM Mg 2+ ), the inducing effects of antibiotics would be even larger than those with higher pH and ionic strength. As aggregation is important to cyanobacteria in either the basic physiology of biofilm formation or the algal bloom, our study demonstrated that low-level antibiotics exert ecological impacts via interfered aggregation. We believe this study will shed light on the mechanisms underlying antibiotic-induced biofilm formation and help with the evaluation of the environmental and ecological risks of antibiotics and other emerging pollutants.
Nitrilase-catalysed desymmetrization of 3-substituted glutaronitriles to optically active 3-substituted 4-cyanobutanoic acid offers an attractive approach to access chiral β-substituted γ-amino acids, an important moiety in pharmaceuticals. In this study, we employed enzyme-substrate docking and alanine scanning to determine the key amino acid residues which have a positive effect on the activity and stereoselectivity of a nitrilase from Synechocystis sp. PCC6803 (SsNIT). Then, site-saturation mutagenesis and combinatorial mutagenesis of the positive amino acid residues (H141, P194, M197, I201 and F202) were performed, and a double mutant (P194A/F202V) and a triple mutant (P194A/I201A/F202V) with high activity and stereoselectivity were identified for desymmetrization of 3-substituted glutaronitriles to afford (S)-3-substituted-4-cyanobutanoic acids with a high space–time productivity of up to 488 g L−1 d−1. Molecular calculation suggests that the enzymatic activity improvement may be due to the enlargement of the substrate binding cavity. It is interesting that the stereoselectivity is enhanced simultaneously.
Tao Lu,Nuohan Xu,Qi Zhang,Zhenyan Zhang,Andries Debognies,Zhigao Zhou,Liwei Sun,Haifeng Qian
Glyphosate , one of the most popular herbicides, has become a prominent aquatic contaminant because of its huge usage. The eco-safety of glyphosate is still in controversy, and it is inconclusive how glyphosate influences aquatic microbial communities . In the present study, the effects of glyphosate on the structure and function of microbial communities in a freshwater microcosm were investigated. 16S/18S rRNA gene sequencing results showed that glyphosate treatment (2.5 mg L −1 , 15 days) did not significantly alter the physical and chemical condition of the microcosm or the composition of the main species in the community, but metatranscriptomic analyses indicated that the transcriptions of some cyanobacteria were significantly influenced by glyphosate. The microbial community enhanced the gene expression in pathways related to translation, secondary metabolites biosynthesis, transport and catabolism to potentially withstand glyphosate contamination. In the low phosphorus (P) environment, a common cyanobacterium, Synechococcus , plays a special role by utilizing glyphosate as P source and thus reducing its toxicity to other microbes, such as Pseudanabaena . In general, addition of glyphosate in our artificial microcosms did not strongly affect the aquatic microbial community composition but did alter the community’s transcription levels, which might be potentially explained by that some microbes could alleviate glyphosate’s toxicity by utilizing glyphosate as a P source.
危险品化学品经营许可证（带存储）