Insights into chromate resistance of Shewanella decolorationis LDS1.

The Shewanella genus is well known for its genetic diversity, its outstanding respiratory capacity and its high potential for bioremediation. Here, a novel strain isolated from sediments of the Indian Ocean was characterized. A 16S rRNA analysis indicated that it belongs to the S. decolorationis species. It was named Shewanella decolorationis LDS1. This strain presented an unusual ability to grow efficiently from 24 °C to 40 °C, without apparent modifications of its metabolism as shown by testing respiratory activities or carbon assimilation and in a wide range of salt concentrations. Moreover, S. decolorationis LDS1 tolerates high chromate concentrations. Indeed, it was able to grow in the presence of 4 mM chromate at standard temperature and 3 mM at 40 °C. Interestingly, whatever the temperature, when the culture reached the stationary phase, the strain reduced the chromate present in the growth medium. In addition, S. decolorationis LSD1 degrades different toxic dyes including anthraquinone-, triarylmethane- and azo-dye. Thus, compared to S. oneidensis, this strain presented better capacity to cope with various abiotic stresses in particular at high temperatures. The analysis of genome sequence preliminary data indicated that, in contrast to S. oneidensis and S. decolorationis S12, S. decolorationis LDS1 possesses the phosphorothioate modification machinery that has been described to participate to survival against various abiotic stresses by protecting DNA. We demonstrate that its heterologous production in S. oneidensis allows it to resist higher concentrations of chromate.Importance Shewanella species have long been described as interesting microorganisms in regards to their ability to reduce many organic and inorganic compounds including metals. However, members of the Shewanella genus are often depicted as cold water microorganisms although usually their optimal growth temperature ranges around 25-28 °C under laboratory growth conditions. S. decolorationis LDS1 is highly attractive since its metabolism allows it to develop efficiently from 24 to 40 °C conserving its ability to respire alternative substrates and to reduce toxic compounds such as chromate or toxic dyes. Our results clearly indicate that this novel strain has the potential to be a powerful tool for bioremediation and unveil one of the mechanisms involved in the chromate resistance.