BackgroundChlorophenols are environmental contaminants, which are highly toxic to living beings due to their carcinogenic, mutagenic and cytotoxic properties. Bacterial degradation has been considered a cost-effective and eco-friendly method of removing chlorophenols, compared to the traditional physical–chemical processes.ResultsIn this study, we first developed an efficient process for the biodegradation of chlorophenols by magnetically immobilized Rhodococcus rhodochrous cells. R. rhodochrous DSM6263 degrades chlorophenols following the first step of hydroxylation at the ortho-positions of chlorophenolic rings. The cells immobilized by k-carrageenan with 9 g/L Fe3O4 nanoparticles could efficiently degrade 2-chlorophenol, 4-chlorophenol, 2,3-dichlorophenol and their mixture, which were even higher than those by free cells. The magnetically nanoparticle-immobilized cells could be used at least for six cycles.ConclusionGiven the much easier separation by an external magnetic field and high degradation efficiency, this study provides a promising technique for improving biocatalysts used in the bioremediation process for chlorophenols in wastewater.

Plants produce a wide variety of secondary metabolites that are highly nutraceutically and pharmaceutically important. Isothiocyanates, which are found abundantly in cruciferous vegetables, are believed to reduce the risk of several types of cancers and cardiovascular diseases. The challenges arising from the structural diversity and complex chemistry of these compounds have spurred great interest in producing them in large amounts in microbes. In this study, we aimed to synthesize benzyl isothiocyanate in Escherichia coli via gene mining, pathway engineering, and protein modification. Two chimeric cytochrome P450 enzymes were constructed and functionally expressed in E. coli. The E. coli cystathionine β-lyase was used to replace the plant-derived C-S lyase; its active form cannot be expressed in E. coli. Suitable desulfoglucosinolate:PAPS sulfotransferase from Arabidopsis thaliana ecotype Col-0 and myrosinase from Brevicoryne brassicae were successfully mined from the database. Biosynthesis of benzyl isothiocyanate by the combined expression of the optimized enzymes in vitro was confirmed by gas chromatography-mass spectrometry analysis. This study provided a proof of concept for the production of benzyl isothiocyanate by microbially produced enzymes and, importantly, laid the groundwork for further metabolic engineering of microbial cells for the production of isothiocyanates.

Summary Hazardous materials, such as heavy metals, are the major sources of health risk. Using genetically modified organisms (GMOs) to dispose heavy metals has the advantages of strong environmental compatibility and high efficiency. However, the biosecurity of GMOs used in the environment is a major concern. In this study, a self‐controlled genetic circuit was designed and carefully fine‐tuned for programmable expression in Pseudomonas putida KT2440, which is a widely used strain for environmental bioremediation. The cell behaviours were controlled by automatically sensing the variation of Hg2+ concentration without any inducer requirement or manual interventions. More than 98% Hg2+ was adsorbed by the engineered strain with a high cell recovery rate of 96% from waterbody. The remaining cells were killed by the suicide module after the mission was accomplished. The escape frequency of the engineered P. putida strain was lower than 10−9, which meets the recommendation of US NIH guideline for GMOs release (<10−8). The same performance was achieved in a model experiment by using natural lake water with addition of Hg2+. The microbial diversity analysis further confirmed that the remediation process made little impact on the indigenous ecosystem. Thus, this study provides a practical method for environmental remediation by using GMOs.