Responses Of A. Ferrooxidans Upon Acid And Organic Extractant Stress Respectively

Acidithiobacillus ferrooxidans is the typical strain in leaching community. In practical leaching, the community is exposed to unfavorable conditions, such as over-acid environment or toxic organic extractant. In this case, the growth and metabolism of the leaching community are stressed. While the leaching process required the active participation of leaching community, it is necessary to study the characteristics of leaching community under such stimulus. In this study, the typical leaching strain A. ferrooxidans is chosen. Considering the symbiosis between autotrophic A. ferrooxidans and heterotrophic Acidiphilum Acidophilum (Aph. acidophilum) suggested in9K with Fe2+, the mix-culture of these two strains is chosen as well.This study applied the technology of microarray to reveal the characteristics of A. ferrooxidans under acid stress. The results show that A. ferrooxidans performs acid resistance mechanisms mainly from the following aspects:adjustments of cell envelop structure by inducing Omp85; control of proton influx by inducing plasma-membrane proton-efflux P-type ATPase and depressing ATP synthase; buffering the cytoplasm by inducing related substance such as carbonic anhydrase; induced regulation based on RpoS. Based on the above strategies, A. ferrooxidans is able to survive in face of the shift down of the extraeellular pH to pH1.2.In the mix-culture of A. ferrooxidans and Aph. acidophilum with S0as energy source, the growth of A. ferrooxidans definitely predominates in the early stage, however, Aph. acidophilum quickly exceeds A. ferrooxidans till A. ferrooxidans reaches stationary phase, soon Aph. acidophilum becomes the predominate strain as A. ferrooxidans enters decline phase. Based on the above phenomenon, it could be suggested that the growth of Aph. acidophilum depends on A. ferrooxidans, while its growth could bring negative effect to A. ferrooxidans at the same time.Real-time quantitative PCR is applied to study the characteristics of leaching bacteria under stress brought by organic extractant P204, and results reveal that different resistance abilities are suggested in A. ferrooxidans while mix-cultured with Aph. acidophilum. In pure culture of A. ferrooxidans, it could perform related resistance mechanisms against the stress brought by P204, however, the mechanisms only present actively till A. ferrooxidans is stressed for a while, approximately10to20minutes. The conclusion is based on the expression discrepancies of related genes. Rpos, which is considered the signal of active resistance mechanism, shows the tendency of up-regulation as the stress went on, and it is induced till A. ferrooxidans is stressed for20min. The similar tendency could be seen in genes related to stress resistance, such as RpoE, RpoN, Omp40, Phosphoheptose isomerase/cytidylyltransferase, PhnL, PhnK and Universal stress family protein(AFE2259, AFE2183, AFE2133), thus it could be safely concluded that A. ferrooxidans needs a recuperation period after the procedure of extraction in industry application as resistance mechanisms against the stress brought by P204are active till then.In the mix-culture, resistance ability of A. ferrooxidans seems to differ from the one in pure culture. According to the expression discrepancies of RpoS, it is induced at10min while the up-regulation doesn’t go on as the stress is on. Besides, RpoE, PhnK and Universal stress family protein (AFE2183) are slightly induced when A. ferrooxidans is stressed for5min, then they are not significantly regulated as the stress is on, among all the detected genes which are related to stress resistance. Combined with the growth curve of mix-culture upon stress from P204, that is, A. ferrooxidans declinced quickly upon the stress, it could be suggested the resistance mechanisms in A. ferrooxidans of mix-culture are weaker than that of pure culture, and its growth and metabolism are effected as the stress from P204continues. In this case, A.ferrooxidan in mix-culture might need a longer recuperation period after the procedure of extraction in industry application as its resistance ability seems to be weaker than A.ferrooxidan in pure culture.