The EmhABC efflux pump in Pseudomonas fluorescens LP6a is involved in naphthalene tolerance but not efflux

Glycerol-assisted degradation of dibenzothiophene by Paraburkholderia sp. C3 is associated with polyhydroxyalkanoate granulation

Glycerol is a biodiesel byproduct. In the present study, glycerol was used as a co-substrate during biodegradation of dibenzothiophene (DBT) by Paraburkholderia sp. C3. Polycyclic aromatic hydrocarbons (PAHs) are a group of persistent, ubiquitous and carcinogenic chemicals found in the environment. DBT is a major sulfur-containing PAH. The chemical properties of DBT make it an ideal model pollutant for examining the bioremediation of higher molecular weight PAHs. Bioremediation uses microbial catalysis for removal of environmental pollutants. Environmental microorganisms that encounter aromatic substrates such as heterocyclic PAHs develop unique characteristics that allow the uptake and assimilation of these cytotoxic substrates. Microbial adaptations include changes in membrane lipid composition, secretion of surface-active compounds and accumulation of lipid granules to withstand chemical toxicity. Biostimulation using more readily metabolized substrates can increase the biodegradation rate of PAHs, but the molecular mechanisms are not well understood. We analyzed the DBT biodegradation kinetics in C3, proteome changes and TEM micrographs in different culturing conditions. We utilized 2-bromoalkanoic lipid metabolic inhibitors to establish a correlation between polyhydroxyalkanoate (PHA) granule formation and the enhancement of DBT biodegradation induced by glycerol. This is the first description linking PHA biosynthesis, DBT biodegradation and 2-bromoalkanoic acids in a Paraburkholderia species.

Biodegradation of aromatic pollutants meets synthetic biology

Ubiquitously distributed microorganisms are natural decomposers of environmental pollutants. However, because of continuous generation of novel recalcitrant pollutants due to human activities, it is difficult, if not impossible, for microbes to acquire novel degradation mechanisms through natural evolution. Synthetic biology provides tools to engineer, transform or even re-synthesize an organism purposefully, accelerating transition from unable to able, inefficient to efficient degradation of given pollutants, and therefore, providing new solutions for environmental bioremediation. In this review, we described the pipeline to build chassis cells for the treatment of aromatic pollutants, and presented a proposal to design microbes with emphasis on the strategies applied to modify the target organism at different level. Finally, we discussed challenges and opportunities for future research in this field.

Physico-chemical factors affect chloramphenicol efflux and EmhABC efflux pump expression in Pseudomonas fluorescens cLP6a

Protein synthesis inhibitors such as chloramphenicol and tetracycline may be inducers of efflux pumps such as MexY in Pseudomonas aeruginosa, complicating their use for the treatment of bacterial infections. We previously determined that chloramphenicol, a substrate of the EmhABC efflux pump in Pseudomonas fluorescens cLP6a, did not induce emhABC expression. In this study, we determined the effect of physico-chemical factors on chloramphenicol efflux by EmhABC, and the expression of emhABC. Efflux assays measuring accumulation of (14)C-chloramphenicol in cell pellets showed that chloramphenicol efflux is dependent on growth temperature, pH and concentration of Mg(2+). These physico-chemical factors modulated the efflux of chloramphenicol by 26 to >50%. All conditions tested that decreased the efflux of chloramphenicol unexpectedly induced transcription of emhABC efflux genes. EmhABC activity also effectively suppressed the deleterious effect of chloramphenicol on the cell membrane of strain cLP6a, which may explain why chloramphenicol is not an inducer of emhABC. Our results suggest that the detrimental effect of an antibiotic on cell membrane integrity and fatty acid composition may be the signal that induces emhABC expression, and that inducers of other bacterial efflux pumps may include environmental factors rather than their substrates per se.