LIGHT-ELEMENT ANALYSIS OF INDIVIDUAL BACTERIA BY X-RAY-MICROANALYSIS

A method based on X-ray microanalysis (XRMA) with the transmission ele ctron microscope for measure ment of total amounts of elements in sing le microbial cells has been developed. All major elements in cells exc ept hydrogen can be measured simultaneously, XRMA provided N/C ratios (means +/- standard errors of the mean) for stationary-phase and growi ng Escherichia coli of 0.23 +/- 0.01 and 0.30 +/- 0.01, respectively, while CHN analysis gave values of 0.276 and 0.307, respectively, for s amples from the same cultures. Analyses of free coccoliths from Emilia na huxleyi provided weight fractions close to those of CaCO3: 0.35 +/- 0.01, 0.15 +/- 0.01, and 0.47 +/- 0.01 for calcium, carbon, and oxyge n, 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 betwe en 500 and 5,000 ppm, depending on size. As a single-cell method, XRMA avoids the shortcomings of commonly used fractionation techniques ass ociated with bulk methods, which are based on centrifugation or filtra tion, On the basis of morphology and XRMA, particles may be classified more precisely into groups (e.g., biotic versus abiotic) than is poss ible by bulk methods. Single-cell elemental analysis may provide insig ht into topics like nutritional and energetic status, macromolecular c omposition, and (by multivariate statistics) community structure.