Approaches currently used for remediating acid mine drainage (chiefly active chemical treatment and passive bioremediation systems) have a number of major detractions, including their failure to recover potentially valuable metals from these waters. Bioremediation strategies that utilizereactor-housed microorganisms can circumvent this problem, but have tended not to be widely used due to their relatively high costs. We have devised innovative approaches for remediating mine waters that use acidophilic bacteria to remove metals either as oxidized or reduced phases, usingmodular bioreactors that are designed to operate at minimal cost and to generate products that have commercial value. A composite system is described that combines microbial oxidation of ferrous iron with abiotic precipitation of ferric iron as schwertmannite, a mineral that has commercialvalue as an absorbent of arsenate and other environmental pollutants, and as a pigment. Sulfidogenic bioreactors maintained at acidic pH values are used to selectively precipitate metal sulfides, such as CuS. Tests with synthetic mine drainage containing mixtures of soluble metals confirmedthat these systems can generate relatively pure mineral deposits from complex acid waters. The units are designed to be configured differently, according to the nature of the mine water requiring treatment.

Ideally, cell models should resemble the in vivo conditions; however, in most in vitro experimental models, epithelial cells are cultivated as monolayers, in which the establishment of functional epithelial features is not achieved. To overcome this problem, co-culture experiments with probiotics, dendritic cells and intestinal epithelial cells and three-dimensional models attempt to reconcile the complex and dynamic interactions that exist in vivo between the intestinal epithelium and bacteria on the luminal side and between the epithelium and the underlying immune system on the basolateral side. Additional models include tissue explants, bioreactors and organoids. The present review details the in vitro models used to study host–microbe interactions and explores the new tools that may help in understanding the molecular mechanisms of these interactions.