Copper tolerance of the thermoacidophilic archaeon Sulfolobus metallicus: possible role of polyphosphate metabolism

Abstract

It has been postulated that inorganic polyphosphate (polyP) and transport of metal-phosphate complexes could participate in heavy metal tolerance in some bacteria. To study if such a system exists in archaea, the presence of polyP was determined by the electron energy loss spectroscopy (EELS) procedure and quantified by using specific enzymic methods in Sulfolobus acidocaldarius, Sulfolobus metallicus and Sulfolobus solfataricus. All three micro-organisms synthesized polyP during growth, but only S. metallicus greatly accumulated polyP granules. The differences in the capacity to accumulate polyP between these archaea may reflect adaptive responses to their natural environment. Thus, S. metallicus could grow in and tolerate up to 200 mM copper sulfate, with a concomitant decrease in its polyP levels with increasing copper concentrations. On the other hand, S. solfataricus could not grow in or tolerate more than 1-5 mM copper sulfate, most likely due to its low levels of polyP. Shifting S. metallicus cells to copper sulfate concentrations up to 100 mM led to a rapid increase in their exopolyphosphatase (PPX) activity which was concomitant in time with a decrease in their polyP levels and a stimulation of phosphate efflux. Furthermore, copper in the range of 10 mM greatly stimulated PPX activity in cell-free extracts from S. metallicus. The results strongly suggest that a metal tolerance mechanism mediated through polyP is functional in members of the genus Sulfolobus. This ability to accumulate and hydrolyse polyP may play an important role not only in the survival of these micro-organisms in sulfidic mineral environments containing high toxic metals concentrations, but also in their applications in biomining.

The influence of single and combined effects of Zn, Cu and temperature on microbial growth

“…Zn was also observed to stimulate the PXX activity of A. ferrooxidans at 1-2 μM concentrations; however, this stimulation effect was only half compared to that of exposure to Cu (Alvarez and Jerez, 2004). Stimulation effect of Zn on the PXX activity was also seen for S. metallicus in the micromolar range, similarly lower than of the Cu effect (Remonsellez et al, 2006), both consistent with our observations with Arthrobacter sp. Stimulation by Cu was also observed for the superoxide dismutase (SOD) activity of the strain N6 of the yeast Cryptococcus sp.…”

“…Similar stimulatory effects of Cu have also been observed for exopolyphosphatase (PPX) activity of A. ferrooxidans up to 1-2 μM Cu, where inhibition in the PXX activity occurred for Cu concentrations greater than 5 μM (Alvarez and Jerez, 2004), and up to 10 μM Cu for the archaeon Sulfolobus metallicus (Remonsellez et al, 2006). Zn was also observed to stimulate the PXX activity of A. ferrooxidans at 1-2 μM concentrations; however, this stimulation effect was only half compared to that of exposure to Cu (Alvarez and Jerez, 2004).…”

Heavy Metal Resistance Strategies of Acidophilic Bacteria and Their Acquisition: Importance for Biomining and Bioremediation

“…In the environment of biomining microorganisms, copper and other nominal metal concentrations are one or two orders of magnitude greater than those tolerated by neutrophiles (Remonsellez et al, 2006;Orell et al, 2010;Orell et al, 2013). However, since the growth conditions of these two types of bacteria are completely diff erent the comparison cannot be directly made.…”

“…In this regard, polyP granules have also been observed in electron micrographs of thin sections of T. arsenitoxydans (Arséne-Ploetze et al, 2010). Thus a polyP-dependent system for Cu-resistance has been proposed for A. ferrooxidans (Alvarez and Jerez, 2004) and S. metallicus (Remonsellez et al, 2006), reviewed in Orell et al, (2012). This resistance mechanism is based on the observed in vitro activation of PPX by the presence of intracellular copper (Alvarez and Jerez, 2004).…”

Phosphate-Mediated Remediation of Metals and Radionuclides

“…In response to the local geochemistry of contaminated environments, production of intracellular polyphosphate provides microorganisms with a means to sequester toxic ions within the cell cytosol as well as the regulation of gene(s) expressed in response to cellular stress (e.g., DNA repair, RNA polymerase sigma factor, and pH extremes) [55,[127][128][129][130][131]. The reactivity of cytosolic polyphosphates has been shown to facilitate intracellular sequestration of Cd, Cu, Hg, Pb, U, and Zn in genetically engineered bacterial strains as well as naturally occurring archaeal and bacterial strains [52,55,[132][133][134][135][136]. Electron microscopy analyses of cells exposed to these elements demonstrated intracellular localization with phosphate-rich granules, suggesting that contaminant sequestration may be achieved by polyphosphates and may protect sensitive cytosolic molecules from oxidative damage.…”