The inorganic ion content of native aquatic bacteria.

In this study we have quantified the ionic content and volume of native aquatic, and two cultured bacteria, by X-ray microanalysis (XRMA) in the transmission electron microscope (TEM). The cellular concentrations of magnesium (means of 630 and 710 mM) were more than an order of a magnitude higher than the outside concentrations. The internal concentrations of sodium were on 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 indicated that organic solutes are not likely to be present at significant concentrations. The estimated charge of inorganic ions (Na, Mg, P, Cl, K, and Ca) gave a positive net internal charge for most cells. However, in cultures of Vibrio natriegens, the high internal chloride concentration made the net inorganic charge negative in these cells. Our results suggest that growing marine bacterioplankton have an internal environment in which magnesium is the dominating cation. These results suggest that actively growing marine bacteria are physiologically adapted to high internal concentrations of both magnesium and chloride.

Light element analysis of individual bacteria by x-ray microanalysis.

A method based on X-ray microanalysis (XRMA) with the transmission electron microscope for measurement of total amounts of elements in single microbial cells has been developed. All major elements in cells except hydrogen can be measured simultaneously. XRMA provided N/C ratios (means (plusmn) standard errors of the mean) for stationary-phase and growing Escherichia coli of 0.23 (plusmn) 0.01 and 0.30 (plusmn) 0.01, respectively, while CHN analysis gave values of 0.276 and 0.307, respectively, for samples from the same cultures. Analyses of free coccoliths from Emiliana huxleyi provided weight fractions close to those of CaCO(inf3): 0.35 (plusmn) 0.01, 0.15 (plusmn) 0.01, and 0.47 (plusmn) 0.01 for calcium, carbon, and oxygen, respectively. Calibration is based on monodisperse latex beads and on microdrops of defined compounds. Elements in particles in the size range from 5 fg to 500 pg are measured with a relative precision between 500 and 5,000 ppm, depending on size. As a single-cell method, XRMA avoids the shortcomings of commonly used fractionation techniques associated with bulk methods, which are based on centrifugation or filtration. On the basis of morphology and XRMA, particles may be classified more precisely into groups (e.g., biotic versus abiotic) than is possible by bulk methods. Single-cell elemental analysis may provide insight into topics like nutritional and energetic status, macromolecular composition, and (by multivariate statistics) community structure.