I am not sure if this is the correct section, as this topic isn't about medical science. Nevertheless, it's about bacteria and this is the microbiology subsection. Please move if otherwise.

 

In wastewater treatment plants, nitrifying bacteria are used to convert ammonia to nitrite and then to nitrate, the first step of Nitrogen removal process. There are other physical/chemical treatment systems that are used for the same purpose as well.

 

As far as I know, desalination relies on physical/chemical systems to remove salt and minerals from saline water, and desalination methods have thus far been energy intensive (thus expensive), without providing an effective solution for resulting brine or salt.

 

Some microorganisms exist and survive in the dead sea, for example, but they do not remove salt from their environment in any significant degree to impact salinity of the entire water body.

 

Are there microorganisms that remove salt from their environment? Can such a microorganism even exist?

What's the status of research into biological desalination methods?

I honestly cannot think of a mechanism that would allow desalination. Typically, bioremediation is achieved by allowing the bacteria to oxidize or reduce the compounds (they often use them as electron donor or acceptors). For simple chemcials, including e.g. uranium or chromium this results in decreased water solubility. The precipitated metal can then be removed. For more complex compounds degradation to some less toxic compounds or even CO2 may be possible. However, salinity is typically determined by sodium chloride. There is little metabolically that they can do with it. For instance, there are not really any oxidation states that can be exploited.