Tungsten accumulation by highly tolerant marine hydrothermal Sulfitobacter dubius strains carrying a tupBCA cluster

Tungsten (W) has industrial and economic importance, and is in the European Union list of metals with a high supply risk. It is used by living organisms, which transport it into the cell, in the form of tungstate ion (WO₄^2-), using three different ABC-type transporters from the specific W-uptake system coded by tupABC gene cluster. In this study, strains from a collection recovered from deep-sea hydrothermal sediments were selected according to their ability to tolerate metals and to possess the tup genetic determinants. Three multimetal-tolerant strains, Sulfitobacter dubius NA4, As(V)4 and Sb5, were chosen. The strains were able to grow in the presence of high tungsten concentrations and their growth was unaffected by 1mM tungsten. Moreover, strain Sb5 was able to accumulate up to 52μg W mg^-1 protein. Their tup genes were shown to be organized as tupBCA, which is not the most usual gene arrangement. All three strains had the classical TupA conserved motif TTTS, comprising a first Thr replaced by a Val, which seems to be a common feature of the genus Sulfitobacter. This study was an important first step in the exploration of new biological strategies for recovering tungsten from natural or anthropogenic W-impacted environments.