The inorganic ion content of native aquatic bacteria

In this study we have quantified the ionic content and volume of native aqu atic, and two cultured bacteria, by X-ray microanalysis (XRMA) in the trans mission electron microscope (TEM). The cellular concentrations of magnesium (means of 630 and 710 mM) were more than an order of a magnitude higher th an the outside concentrations. The internal concentrations of sodium were o n average 50-180 mM, and the [K+]/[Na+] ratios were in the range of 0.1-0.5 ; lowest for apparently nonactive bacteria. Magnesium and chloride probably act as the major components of cell turgor, since no other inorganic ions were present in comparable amounts. Our carbon and nitrogen measurements in dicated that organic solutes are not likely to be present at significant co ncentrations. The estimated charge of inorganic ions (Na, Mg, P, Cl, K, and Ca) gave a positive net internal charge for most cells. However, in cultur es of Vibrio natriegens, the high internal chloride concentration made the net inorganic charge negative in these cells. Our results suggest that grow ing marine bacterioplankton have an internal environment in which magnesium is the dominating cation. These results suggest that actively growing mari ne bacteria are physiologically adapted to high internal concentrations of both magnesium and chloride.