Elemental C, N, and P cell content of individual bacteria collected at the Bermuda Atlantic Time-series Study (BATS) site

Accurate assessments of the true elemental cellular content of carbon (C), nitrogen (N), and phosphorus (P) in bacteria have been a major difficulty in microbial research for some time. This study is the first to present single-cell elemental C, N, and P measurements on natural populations of bacteria from the Sargasso Sea using a transmission electron microscope (TEM) equipped with an X-ray detector unit. Elemental cell content showed a best fit as a power function of the cell size, and smaller bacteria had significantly more elemental C, N, and P per cell volume than the larger ones (scaling factor a < I ), contrary to coastal, brackish, and freshwater systems, the bacteria collected in this study appeared to have a molar elemental P:N close to the Redfield ratio of 0.063 (N: P = 16). The geometric mean of C per cell volume analyzed in this study (148 fg C μm -3 ) was higher than any other estimates reported from coastal and brackish water systems. Total amount of bacterial C calculated from abundance estimates requires an average conversion factor, and the choice of a representative bacterial cell volume is therefore critical. We were able to demonstrate that the outcome of biomass assessments is highly dependant on the choice of cell-specific conversion factors. By applying cell volumes previously reported from the BATS site, the average 0-250 m depth integration of bacterial C between 1991 and 1996 ranged between 1.7 and 2.5 times less than other recent biomass estimates for these waters.