The elemental composition of bacteria: A signature of growth conditions?

X-ray microanalysis combined with Transmission Electron Microscopy (TEM) has been employed to measure cell quotas of P:C, N:C and O:C of individual cells from cultures and natural microbial communities. The relevance of such data for evaluation of nutrient availability and growth is discussed according to the Droop model. Using minimum subsistent quotas of 0.031 (P:C) and 0.17 (N:C) and μmax of 1 h−1 we have been able to identify some of the criteria for nutrient limited growth, but energy/carbon limitation will interfere with interpretation of these data. An additional signature for growth limitation may be the O:C ratio for which preliminary data indicate values of >0.40 for growing cells and <0.25 for dormant or stationary phase cells.