Spectroscopic investigation of the interaction between extracellular polymeric substances and tetracycline during sorption onto anaerobic ammonium-oxidising sludge.

In this study, the interaction between extracellular polymeric substances (EPS) and tetracycline during sorption onto anaerobic ammonium-oxidising (anammox) sludge was investigated. The results showed that EPS significantly enhanced the adsorption efficiency of tetracycline by sludge, and the adsorption data were better fitted with the pseudo-second-order kinetics model. Further, the concentration of proteins in the EPS decreased from 12.31 ± 0.42 to 6.82 ± 0.46 mg/gVSS for various tetracycline dosages (0-20 mg/L), whereas the concentration of polysaccharides did not change. Multiple spectroscopic methods were used to analyze the interaction between EPS and tetracycline. A three-dimensional excitation-emission matrix revealed that the fluorescence intensity of protein-like substances obviously decreased with the increasing addition of tetracycline. According to synchronous fluorescence spectra analysis, static quenching was the major quenching process and there was one type of binding site in the protein-like substances. Additionally, two-dimensional correlation spectroscopy showed that tryptophan-like aromatic protein was more susceptible to tetracycline binding than tyrosine-like aromatic protein. Moreover, the main functional groups involved in complexation of tetracycline and EPS were C-O, C-C and C-N (stretching vibration) and the pyrrole ring of the tryptophan side chain. This study provides useful information on the interaction between EPS and tetracycline and demonstrates the role of EPS in protecting microorganism from tetracycline in the anammox process.

Differential expression of foxo genes during embryonic development and in adult tissues of Xenopus tropicalis.

The forkhead-box transcription factors of O subfamily (FOXO) play important roles in regulation of various biological functions. We cloned foxo1, foxo3, foxo4, and foxo6 from Xenopus tropicalis (hereafter X. tropicalis), and examined their expression in embryos and adult tissues. Maternal transcripts of foxo1 and foxo3 genes are detected within the animal half of the early embryo, their zygotic transcripts show distinct patterns. At late tailbud stages, foxo1 expression is observed mainly in eye, brain, branchial arches, and pronephros. In addition to eye, brain, branchial arches and pronephros, foxo3 expression is also evident in heart and somites. Foxo4 expression was not detected in oocytes. At late tailbud stages, foxo4 is mainly expressed in eye, brain, branchial arches and otic vesicle. Foxo6 expression was not detectable until stage 36, with a specific expression in nasal pits. Obvious expression of foxo1, foxo3 and foxo4, but not foxo6, is detected by RT-PCR both in oocytes and in embryos at examined stages. The expression of foxo1, foxo3 and foxo4 is observed in all tested adult tissues including heart, muscle, liver, lung, stomach and small intestine, while foxo6 is only detectable in stomach and small intestine. The differential expression pattern of foxo genes suggests that they exert distinct functions during embryonic development and in various organs of X. tropicalis.