Biofilm dynamics and EPS production of a thermoacidophilic bioleaching archaeon

Bioleaching of metal sulfides represents an interfacial process where biofilm formation is important in the initial steps of this process. In technical applications of bioleaching, such as reactor leaching in the temperature range of 50 up to 90 °C and also in (self-heating) heaps, thermophilic archaea play an important role and often are the leaching organisms of choice. Nevertheless, to date there is little information available on the interactions between thermoacidophilic archaea and their natural mineral substrates such as pyrite. Especially for extracellular polymeric substances (EPS) of archaea and their biofilms in bioleaching environments information is rather limited. The present work focused on investigations of biofilm dynamics and EPS production of the thermoacidophilic archaeon Acidianus sp. DSM 29099 under bioleaching conditions. The results show that biofilms are dispersed non-homogeneously on pyrite. Large parts of the pyrite surfaces remain free of cells. Cell detachment from pyrite results in microbial "footprints" which, based on lectin binding assays, consist of mannose, glucose and fucose containing compounds. A monolayer biofilm develops on pyrite after 2-4 days of incubation. In addition, the pyrite surface is covered with a layer of organic compounds. EPS analysis indicates the presence of proteins, polysaccharides and uronic acids, the composition of which varies according to substrate and lifestyle (i.e. planktonic, biofilm cells). This report provides insight into EPS and biofilm characteristics of thermophilic archaea and improves understanding of the mineral-microbial-biofilm interfacial interactions in extreme environments. Moreover, the results on interaction dynamics of archaeal microbial consortia will facilitate the understanding of thermophilic bioleaching.