Characterization of Attachment and Growth of Thiobacillus denitrificans on Pyrite Surfaces

Abstract

Anaerobic growth and attachment of the autotrophic denitrifying bacterium Thiobacillus denitrificans on pyrite surfaces were studied. Polished pyrite slabs were exposed to T. denitrificans for 1 to 9 weeks. The reacted pyrite surfaces were imaged with scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). Cells were observed as isolated attached cells, cells in division and cells forming microcolonies embedded in organic films. Bacteria began to colonize pyrite surfaces after 1 week, forming microcolonies after 3 weeks. The rate of colonization of the pyrite surface was around 35 cells mm−2 h−1 for the 3-week period. After 9 weeks, larger areas of the pyrite surface were covered by organic films. Bacterial enumeration on the pyrite surface and in solution showed that most of the cells were not attached to the mineral surface. Nevertheless, both attached and free-living bacteria probably contributed to pyrite-driven denitrification. The results may be applied to the natural environment to better understand pyrite-driven denitrification in aquifers and to improve the long-term performance of bioremediation processes using pyrite.