The microorganisms would die from because the water would move out of the cells of the microorganisms by osmosis and the cytoplasm would become dehydrated, killing the cells.
The brine solution would have a lower osmotic potential than the cytoplasm of the cell, which simply means that there would be more water in the cell than in the solution. Water would move down the concentration gradient and exit the cell by the process of osmosis. This would result in the death of the cells.
