What causes bacteria to die in an extremely salty environment is dehydration due to the loss of osmotic balance in their cells.
Water molecules would normally move from the region of high water potential or low solute concentration to the region of low water potential or high solute concentration through a biologically permeable membrane.
<em>An extremely salty environment would be hypertonic to the cells of bacteria and the cell walls of bacteria act as biologically permeable membranes. Hence, the bacteria cells lose water due to the osmotic movement of water from their cells to the surrounding salty environment. </em>
