Study On The Function Of Quorum Sensing In Acidithiobacillus Ferrooxidans

Quorum sensing (QS) is a cell-to-cell signaling system in response to their population density by producing, releasing and detecting small signal molecules. A variety of physiological processed of bacterial species such as bioluminescence, pathogenesis, antibiotic production, motility, plasmid transfer, and biofilm formation were found to be regulated by quorum sensing. Recently, quorum sensing signal system has been detected in Acidithiobacillus ferrooxidans(A. ferrooxidans). However, little is known on QS function in A. ferrooxidans.In this study, synthetic (5Z)-4-bromo-5-(bromomethylene)-2(5H)-furanone (FUR) was prepared as QS inhibitor. The effects of the FUR compound on AHLs production in A. ferrooxidans ATCC23270 were examined, we also examined the impact of metal ions and FUR compound on afel and afeR expressions. Data showed clearly that the FUR compound used in our study could significantly decline the expression of afel and afeR genes in A. ferrooxidans ATCC23270 and further to decrease its production of AHLs at a low concentration (0.01μg/mL 0.1μg/mL), so FUR compound is an efficient blocker to QS in A. ferrooxidans.We attempted to correlate the quorum sensing in A. ferrooxidans and its resistance to heavy metal ions, especially for copper ion. Seven kinds of heavy metals (Ni2+, Co2+, Cu2+, Mn2+, Hg2+ Mg2+ and Zn2+) of three A. ferrooxidans strains (ATCC23270, ATCC19859, BY-3) in the presence of various concentrations of FUR compound were examined. Our results showed that different A. ferrooxidans strains exhibited different sensitivity to seven soluble metal ions, the resistances of these strains to the metal ions decreased in the presence of FUR compound and showed different sensitivity to FUR compound in a dose dependent manner. The transcription levels of the A. ferrooxidans afel, afeR, afe0329 and afe0454 genes were determined by quantitative real-time RT-PCR, results showed that the expressions of QS associated gene afeI and afeR were significantly increased in the presence of 50 mM Cu2+, when we treated A. ferrooxidans with both 50 mM Cu2+ and 0.01μg/mL FUR compound, there was no increase any more in expressions of afel and afeR genes, the increase tendency of copper ion resistance associated gene afe0329 and afe0454 expressions were significantly repressed. It can be concluded that QS in A. ferrooxidans was involved in its resistance to Cu2-, and probably in its resistance to other metal ions. A. ferrooxidans adsorb onto the mineral surface is an important process for mineral dissolution in natural environments and industrial operations. The attachment of the bacteria to a natural pentlandite was determined, Our preliminary results showed tendencies of FUR compound to inhibit the attachment of A. ferrooxidans ATCC23270 to pentlandite, this could be explained by that the compounds interfered with the replenishment of cell EPS, and further to decrease the attachment of cells on the pentlandite surface. In metal dissolution experiment, SEM photos showed that A. ferrooxidans cell could specifically attach to dislocation sites on the pentlandite surface, such as cracks and grain boundaries. While for FUR compound treated sample, we see a thick cell layer was formed on the pentlandite surface which seemed chaos and disorderly. This result suggested that the FUR compound could disturb A. ferrooxidans cells from adsorb selectively to special sites of the pentlandite surface.In the metal dissolution experiment, we found that the amounts of biologically dissolved Ni and Cu were much greater than that produced by pure chemical reaction, in the absence of microorganisms, this result indicated that A. ferrooxidans strain plays an important role in the metal dissolution. While for the FUR treated samples, the dissolved Ni and Cu significantly decreased, and the inhibitory effect on dissolving Ni and Cu last for a long time (60d). So we assume that the metal dissolving process by A. ferrooxidans is probably a population function rather than an individual response. Our data provided us a new strategy to inhibit acid mine drainage (AMD) formation caused by high concentration of dissolved metal through disturbing the quorum sensing signal system in A. ferrooxidans.