Differential utilization of cyclic, orthorhombic α- and chain-like polymeric μ-sulfur by Acidithiobacillus ferrooxidans

The differential utilization of cyclic, orthorhombic α-sulfur (α-S) and chain-like polymeric μ-sulfur (μ-S) by Acidithiobacillus ferrooxidans was investigated. The growth and sulfur oxidation results indicated that utilization of μ-S by A. ferrooxidans was clearly different from α-S. Even if the planktonic cells were produced, the fall of pH and the rise of sulfate concentration were the same after 300 h on each substrate, the speeds of the planktonic cells increase, pH decrease and sulfate concentration increase in the earlier cultivation stage were faster on polymeric sulfur compared with the orthorhombic form. The adsorption capacity of the cells was higher on μ-S than on α-S. The results of SEM, DRIFTS and XRD analyses indicated that the surfaces of α-S and μ-S were modified differently by cells. Differential expression of 11 selected sulfur adsorption-activation and metabolism relevant genes was detected by RT-qPCR. The results showed that the expression of the hydrophobic substrate transport proteins and the sulfur metabolism related proteins was up-regulated, and the adsorption and activation related proteins were down-regulated when the cells were grown on μ-S, suggesting that μ-S could be more easily bio-adapted and activated than α-S.