Controlled co-immobilisation of proteins via 4'-phosphopantetheine-mediated site-selective covalent linkage.

In Escherichia coli, acyl carrier protein (ACP) is posttranslationally converted into its active holo-ACP form via covalent linkage of 4'-phosphopantetheine (4'-PP) to residue serine-36. We found that the long flexible 4'-PP arm could react chemoselectively with the iodoacetyl group introduced on solid supports with high efficiency under mild conditions. Based on this finding, we developed site-selective immobilisation of proteins via the active holo-ACP fusion tag, independently of the physicochemical properties of the protein of interest. Furthermore, the molecular ratios of co-immobilised proteins can be manipulated because the tethering process is predominantly directed by the molar concentrations of diverse holo-ACP fusions during co-immobilisation. Conveniently tuning the molecular ratios of co-immobilised proteins allows their cooperation, leading to a highly productive multi-protein co-immobilisation system. Kinetic studies of enzymes demonstrated that α-amylase (Amy) and methyl parathion hydrolase (MPH) immobilised via active tag holo-ACP had higher catalytic efficiency (kcat/Km) in comparison with their corresponding counterparts immobilised via the sulfhydryl groups (-SH) of these proteins. The immobilised holo-ACP-Amy also presented higher thermostability compared with free Amy. The enhanced α-amylase thermostability upon immobilisation via holo-ACP renders it more suitable for industrial application.

Migration of antibiotic resistance genes and evolution of flora structure in the Xenopus tropicalis intestinal tract with combined exposure to roxithromycin and oxytetracycline.

The intestinal flora is one of the most important environments for antibiotic resistance development, owing to its diverse mix of bacteria. An excellent medicine model organism, Xenopus tropicalis, was selected to investigate the spread of antibiotic resistance genes (ARGs) in the intestinal bacterial community with single or combined exposure to roxithromycin (ROX) and oxytetracycline (OTC). Seventeen resistance genes (tetA, tetB, tetE, tetM, tetO, tetS, tetX, ermF, msrA, mefA, ereA, ereB, mphA, mphB, intI1, intI2, intI3) were detected in the intestines of Xenopus tropicalis living in three testing tanks (ROX tanks, OTC tanks, ROX + OTC tanks) and a blank tank for 20 days. The results showed that the relative abundance of total ARGs increased obviously in the tank with single stress but decreased in the tank with combined stress, and the genes encoding the macrolide antibiotic efflux pump (msrA), phosphatase (mphB) and integron (intI2, intI3) were the most sensitive. With the aid of AFM scanning, DNA was found to be scattered short chain in the blank, became extended or curled and then compacted with the stress from a single antibiotic, and was compacted and then fragmented with combined stress, which might be the reason for the variation of the abundance of ARGs with stress. The ratio of Firmicutes/Bacteroides related to diseases was increased by ROX and OTC. The very significant correlation between intI2 and intI3 with tetS (p ≤ 0.001) hinted at a high risk of ARG transmission in the intestines. Collectively, our results suggested that the relative abundance of intestinal ARGs could be changed depending on the intestinal microbiome and DNA structures upon exposure to antibiotics at environmental concentrations.

Effects of Shigella flexneri exposure on development of Xenopus Tropicals embryo and its immune response.

Shigella sp. is a highly infectious intestinal pathogen worthy of serious attention that is widely present in aquaculture water and some other polluted water types and might inhibit embryonic development as a biological pollutant. In this study, acute toxicity tests in which Xenopus tropical embryos were exposed to Shigella flexneri at subpathogenic concentrations (106, 107, and 108 CFU·mL-1) for 96 h were carried out to evaluate toxicity indicators such as mortality, hatching rate, malformation rate and enzyme activity. Meanwhile, the expression of related genes was also studied to reveal the toxicity and mechanism of S. flexneri involved in embryonic development. Under S. flexneri exposure, embryo mortality, heart rate and malformation rate increased, but the hatching rate decreased and even led to embryonic gene misexpression, oxidative stress and immune responses. The results showed that S. flexneri might affect the growth and development of embryos by causing differences in the expression of genes related to embryonic development, oxidative stress and immune disorders. Its target organs are the intestine and heart, whose toxic effects are positively correlated with exposure concentration. This result provides a certain theoretical reference for rational evaluation of the influence of Shigella on the early embryos of amphibians.

Potential reproductive toxicity of multi-walled carbon nanotubes and their chronic exposure effects on the growth and development of Xenopus tropicalis.

The increasing production and use of multi-walled carbon nanotubes (MWCNTs) will inevitably lead to discharge into the environment and exert negative effects on organisms. Many studies have focused on the toxicity of MWCNTs to aquatic animals, but little is known about their possible potential reproductive toxicity. In this study, 6 sexually mature Xenopus tropicalis were exposed to 0.5 and 2.5 mg/L MWCNTs suspensions for 56 days, and the toxicity of MWCNTs to the growth and reproduction of X. tropicalis were studied. The results showed that MWCNTs could inhibit the growth of body, including the testis, ovaries and fat of X. tropicalis. Histopathological section analysis showed that MWCNTs affected the formation of spermatogonia and oocytes, while had no notable effect on the heart or liver. MWCNTs would be accumulated in lungs of X. tropicalis inducing lung cannons. In addition, MWCNTs changed the microbial community structure and diversity of gut microbiota but did not change its abundance significantly. Moreover, MWCNTs could even decrease the fertilized and survival rate of X. tropicalis embryos. These results indicated that chronic exposure to MWCNTs would not only affect the growth and development of X. tropicalis, but also pose a potential risk on their reproduction.

Integrating Spirulina platensis cultivation and aerobic composting exhaust for carbon mitigation and biomass production.

Aerobic composting is an effective way to dispose of organic waste. However, considerable carbon is converted into CO2 and emitted into the atmosphere, which is a waste of the carbon resource and has the potential for the greenhouse gas effect. In this study, an innovative approach coupling aerobic composting exhaust and Spirulina platensis cultivation has been proposed and investigated, resulting in a double-edged solution to mitigating waste and co-generating biomass with a minimal cost of CO2 supplied in the culture. Experimental results showed that the maximum biomass productivity ranged from 56.61 to 58.38 mg·L-1·day-1 was achieved using aerobic composting exhaust as a carbon source. Moreover, the CO2 fixation rates of 46.36 mg·L-1·day-1 and 76.81 mg·L-1·day-1 were obtained by S. platensis cultivation. Finally, the chemical composition analysis of S. platensis biomass obtained in an optimum condition showed an abundance of proteins and lipids, thereby indicating its great potential for biofuel industry.