The Nickel Tolerance Capability And Resistance Mechanism Of Acidithiobacillus Thiooxidans And Leptospirillum Ferriphilium

The mesophilic iron and sulfur oxidizing bacteria, Leptospirillum ferriphilum and Acidithiobacillus thiooxidans are important acidophilic leaching microorganisms commonly thrive in the earth’s most metal-rich environments, and under the selective pressure they develop an indigenous metal tolerance capability.This study reported the effect of Ni2+on the growth and functional gene expression of the pure culture and co-culture of At. thiooxidans A01and L. ferriphilum YSK. The growth characteristics of At. thiooxidans A01and L. ferriphilum YSK in pure culture and co-culture were studied in the presence of different concentration of Ni2+with regard to media pH changes, iron oxidation rates and total bacterial concentrations. Growth characteristics and functional gene expression of the pure culture and co-culture of At. thiooxidans and L. ferriphilum in present of0and100mM Ni2+were monitored with real-time PCR.The maximum tolerated concentrations of At. thiooxidans A01and L. ferriphilum YSK in pure culture were300mM and100mM Ni2+. Compared with the pure culture, the co-culture showed a stronger sulfur and ferrous ion oxidation activity at the high concentration of Ni2+. In co-culture At. thiooxidans A01was able to oxidize sulphur in the presence of1050mM Ni2+, and the initial Fe2+was completely oxidized in the presence of150mM Ni2+by L. ferriphilum YSK.Growth characteristics of At. thiooxidans A01and L. ferriphilum YSK in pure culture or co-culture at0and100mM Ni2+were measured by real time-PCR. The results showed that without metal addition the cell density of L. ferriphilum YSK in co-culture was two times higher than that in pure culture, while the cell density of At. thiooxidans A01in pure culture was twice as many as that in co-culture and had48hours shorter lag phases. Under the condition of100mM Ni2+, the presence of L. ferriphilum YSK not only decreased the lag time of At. thiooxidans A01but also facilitated its growth in co-culture. The cell number of At. thiooxidans A01in co-culture was about5times higher than that in pure culture. Besides, At. thiooxidans A01in co-culture grew faster and had48hours shorter lag phases.In addition, the expression of functional genes involved in metal resistance was evaluated using real-time PCR. The existence of At. thiooxidans in co-culture activated the expression of some metal resistance genes in L. ferriphilum YSK at least16hours in advance. And the expression of some genes encoding specialized metal-exporting proteins for At. thiooxidans A01, like copper resistance protein, heavy metal transport/detoxification protein, and cation diffusion facilitator family transporter protein, were much higher than that in pure culture at105h, which indicated that At. thiooxidans in co-culture tend to chose more efficient pathways to transport nickel ion, ensuring the export of heavy metal was faster and more effective than that in pure culture. All the data indicated that there were synergetic interactions between iron and sulfur oxidizing bacteria under the stress of nickle ion.