RESUMO
Polychlorobiphenyls (PCBs) are toxic and persistent organic pollutants that are widely distributed in the environment. Burkholderia xenovorans LB400 is capable of degrading aerobically an unusually wide range of PCBs. However, during PCB-degradation B. xenovorans LB400 generates reactive oxygen species (ROS) that affect its viability. The aim of this study was to increase the efficiency of PCB-degradation of B. xenovorans LB400 by adding antioxidant compounds that could increase tolerance to oxidative stress. The effect of antioxidant compounds on the growth, morphology and PCB-degradation by B. xenovorans LB400 was evaluated. α-Tocopherol or vitamin E (vitE) and berry extract (BE) increased slightly the growth of strain LB400 on biphenyl, whereas in presence of ascorbic acid or vitamin C (vitC) an inhibition of growth was observed. The growth of B. xenovorans LB400 in glucose was inhibited by the addition of 4-chlorobiphenyl (4-CB). Interestingly, in presence of α-tocopherol the growth of strain LB400 was less affected by 4-CB. By transmission electronic microscopy it was observed that α-tocopherol preserved the cell membranes and improved cell integrity of glucose-grown LB400 cells exposed to 4-CB, suggesting a protective effect of α-tocopherol. Notably, α-tocopherol increased biphenyl and 4-CB degradation by B. xenovorans LB400 in an aqueous solution. The effect of antioxidants compounds on PCB-bioremediation was evaluated in agricultural soil spiked with 2-chlorobiphenyl (2-CB), 4-CB and 2,4'-chlorobiphenyl (2,4'-CB). For bioaugmentation, LB400 cells grown on biphenyl and subsequently incubated with pyruvate were added to the soil. Native soil microbiota was able to remove PCBs. Bioaugmentation with strain LB400 increased strongly the PCB-degradation rate. Bioaugmentation with strain LB400 and biostimulation with α-tocopherol or berry extract increased further the PCB degradation. Half-life of 2,4'-CB decreased by bioaugmentation from 24 days to 4 days and by bioaugmentation in presence of α-tocopherol and berry extract to 2 days. By bioaugmentation with strain LB400, 85% of 2,4'-CB was degraded in 20 days, whereas bioaugmentation with strain LB400 and biostimulation with α-tocopherol or berry extract reduced the time to less than 13 days. This indicates that antioxidant compounds stimulated PCB-degradation in soil. Therefore, the addition of antioxidant compounds constitutes an attractive strategy for the scale-up of aerobic PCB-bioremediation processes.
Assuntos
Antioxidantes/farmacologia , Burkholderia/efeitos dos fármacos , Burkholderia/metabolismo , Bifenilos Policlorados/metabolismo , Poluentes do Solo/metabolismo , Aerobiose , Biodegradação Ambiental/efeitos dos fármacos , Burkholderia/crescimento & desenvolvimento , Burkholderia/ultraestrutura , Cinética , Microscopia Eletrônica de Transmissão , Microbiologia do Solo , alfa-Tocoferol/farmacologiaRESUMO
We report the effects of 4-chlorobiphenyl and biphenyl on the physiology, morphology and proteome of the polychlorobiphenyl-degrader Burkholderia xenovorans LB400. The exposure to 4-chlorobiphenyl decreases the growth of LB400 on glucose, and cells exhibit irregular outer membranes, a larger periplasmic space and electron-dense granules in the cytoplasm. Additionally, lysis of cells was observed during incubation with 4-chlorobiphenyl or biphenyl. Proteome of B. xenovorans LB400 exposed to biphenyl and 4-chlorobiphenyl were analysed by two-dimensional gel electrophoresis. Besides induction of the Bph enzymes of biphenyl catabolic pathways, incubation with 4-chlorobiphenyl or biphenyl results in the induction of the molecular chaperones DnaK and GroEL. Induction of these chaperones, which were also induced during heat shock, strongly suggests that exposure to (chloro)biphenyls constitutes stress conditions for LB400. During growth of LB400 on biphenyl, oxidative stress was evidenced by the induction of alkyl hydroperoxide reductase AhpC, which was also induced during exposure to H(2)O(2). 4-chlorobiphenyl and biphenyl induced catechol 1,2-dioxygenase, as well as polypeptides involved in energy production, amino acid metabolism and transport.