Microbes in High Salt and Metal Contamination

Environmental pollution with toxic metals poses a problem of global concern. Soluble, bioavailable metal ions concomitantly increase the osmotic pressure. Hence, salt and metal stresses are related and understanding the responses to these stresses may be useful for bioremediation of sites contaminated by industrial or agricultural processes. In particular, soils and their microbial communities experiencing salt and metal stresses are reviewed, in addition to tolerance mechanisms of bacteria and fungi. Among the prokaryotic mechanisms to withstand high osmotic pressure, the salt-in and salt-out strategies are shown and combined with metal resistance involving spore formation, biofilm formation, and biomineralization. For fungi, compatible solutes are discussed and combined with intracellular and extracellular metal resistance mechanisms and signal transduction pathways involved in adjusting to stress. Vacuoles can be used by eukaryotic fungi to remove toxic agents from the cytosol. In addition, biomineralization and biofilm formation contribute to stress resilience. The impact of combined stress on soil microbiomes impacting biogeochemical cycles is reviewed.