A preliminary study on the phytoremediation of antibiotic contaminated sediment.

In Vietnam's coastal wetlands, fluoroquinolones, a widely used class of antibiotics in shrimp farming, are frequently detected in sediments of former shrimp farms. This phenomenon could lead to negative impacts on the aquatic ecosystem, since the antibiotic residues could induce changes in the microorganism communities of the water body. The potential of native wetland plants (Acrostichum aureum L. and Rhizophora apiculata Blume Fl. Javae) for phytoremediation of fluoroquinolones (ciprofloxacin and norfloxacin) was investigated. The half-life for each antibiotic was estimated at approximately 10 days in the planted sediment. With respect to the accumulation of ciprofloxacin and norfloxacin in plants, these antibiotics were found mainly in roots. Antibiotic translocation from root to stem and leaves occurred at a low rate. The results showed that A. aureum and R. apiculata can be valuable for the phytoremediation of antibiotic-contaminated sediments. Additionally, the initialfindings of the presence of resistant bacteria indicated that bacteria could play a role in facilitating the phytodegradation.

Determination of the partial reactions of rotational catalysis in F1-ATPase.

Steady-state ATP hydrolysis in the F1-ATPase of the F(O)F1 ATP synthase complex involves rotation of the central gamma subunit relative to the catalytic sites in the alpha3beta3 pseudo-hexamer. To understand the relationship between the catalytic mechanism and gamma subunit rotation, the pre-steady-state kinetics of Mg x ATP hydrolysis in the soluble F1-ATPase upon rapid filling of all three catalytic sites was determined. The experimentally accessible partial reactions leading up to the rate-limiting step and continuing through to the steady-state mode were obtained for the first time. The burst kinetics and steady-state hydrolysis for a range of Mg x ATP concentrations provide adequate constraints for a unique minimal kinetic model that can fit all the data and satisfy extensive sensitivity tests. Significantly, the fits show that the ratio of the rates of ATP hydrolysis and synthesis is close to unity even in the steady-state mode of hydrolysis. Furthermore, the rate of Pi binding in the absence of the membranous F(O) sector is insignificant; thus, productive Pi binding does not occur without the influence of a proton motive force. In addition to the minimal steps of ATP binding, reversible ATP hydrolysis/synthesis, and the release of product Pi and ADP, one additional rate-limiting step is required to fit the burst kinetics. On the basis of the testing of all possible minimal kinetic models, this step must follow hydrolysis and precede Pi release in order to explain burst kinetics. Consistent with the single molecule analysis of Yasuda et al. (Yasuda, R., Noji, H., Yoshida, M., Kinosita, K., and Itoh, H. (2001) Nature 410, 898-904), we propose that the rate-limiting step involves a partial rotation of the gamma subunit; hence, we name this step k(gamma). Moreover, the only model that is consistent with our data and many other observations in the literature suggests that reversible hydrolysis/synthesis can only occur in the active site of the beta(TP) conformer (Abrahams, J. P., Leslie, A. G. W., Lutter, R., and Walker, J. E. (1994) Nature 370, 621-628).