A Pseudomonas fluorescens strain ZY2, isolated from swine wastewater, was used to investigate the synergistic effects of five heavy metals (Pb, Cu, Zn, Cr(VI) and Hg) on bacterial resistance to antibiotics. Results indicate that the combined effects of antibiotic type, heavy metal type and concentration were significant (p < 0.01). Cross-resistance to Hg and antibiotics was the most noticeable. Moreover, the resistance to Hg and cefradine or amoxicillin, and Cr and amoxicillin were synergistic for low heavy metal concentrations, and turned antagonistic with increasing concentrations, while the resistances to Cr or Cu and cefradine, Pb or Cu and amoxicillin, Cu and norfloxacin showed reverse effects. In addition, resistance to Zn and amoxicillin were always synergetic, while resistance to Pb and cefradine or norfloxacin, Cr or Hg and norfloxacin as well as all the heavy metals and tetracycline were antagonistic. These results indicate that bacterial resistance to antibiotics can be affected by the type and concentration of co-exposed heavy metals and may further threaten people’s health and ecological security severely via horizontal gene transfer.

The electricity output from microbial fuel cell (MFC) with a microalgae assisted cathode is usually higher than that with an air cathode. The output of electricity from a photosynthetic microalgae MFC was positively correlated with the dissolved oxygen (DO) level in the microalgae assisted biocathode. However, DO is highly affected by the photosynthesis of microalgae, leading to the low stability in the electricity output that easily varies with the change in microalgae growth. In this study, to improve the electricity output stability of the MFC, a partially submerged carbon cloth cathode electrode was first investigated to use oxygen from both microalgae and air, with synthetic piggery wastewater used as the anolyte and anaerobically digested swine wastewater as the catholyte. When the DO levels dropped from 13.6–14.8 to 1.0–1.6 mg/L, the working voltages in the MFCs with partially submerged electrodes remained high (256–239 mV), whereas that for the conventional completely submerged electrodes dropped from 259 to 102 mV. The working voltages (average, 297 ± 26 mV) of the MFCs with the 50% submerged electrodes were significantly (p < 0.05) higher than with other partially or completely submerged electrodes. The associated maximum lipid production from wastewater was 250 ± 42 mg/L with lipid content of 41 ± 6% dry biomass. Although the partially submerged electrode had no significant effects on lipid production or nitrogen removal in wastewater, there was significant improvement in the stability of the electricity generated under variable conditions.

In this study, the interaction between extracellular polymeric substances (EPS) and tetracycline during sorption onto anaerobic ammonium-oxidizing (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.