Content of carbon, nitrogen, oxygen, sulfur and phosphorus in native aquatic and cultured bacteria

The content of carbon, nitrogen, oxygen, phosphorus and sulfur was measured in individual cells from 6 native aquatic samples and 4 samples of cultured bacteria by X-ray microanalysis using a transmission electron microscope (TEM). The molar C N:P ratio for the pooled sample was 50:lO:l From length and width measurements of unfixed air-dried cells we estimated cell volumes over a total range of 0.0026 to 15.8 pm3. and mean C:volume ratios of 30 to 162 fg for the samples included. For the marine samples we found mean N:C ratios of 0.25 to 0.28, while cells from fresh or brackish waters had mean N:C ratios of 0.17 to 0.20, indicating differences in nutrient availability. The P:C ratios for the samples analyzed varied from 0.040 to 0.090, with a pooled mean of 0.052, which is approximately twice that of the Redfield ratio for PC. For 0:C ratios we estimated a pooled mean of 0.37 and a range of 0.22 to 0.77 for all samples. We may conclude that slow-growing or non-growing cells have low 0 C ratios. The mean S:C ratio for all samples was 0.031, with a range of 0 016 to 0.084 for the sample means. A general conclus~on is that single-cell analyses of elemental composition give important information on the physiological conditions of cells and on possible nutrient limitations. The rationale for this is the assumption that changes in macromolecular composition are due to nutrient availability.