Use of high temperature catalytic oxidation (HTCO) to measure carbon content of microorganisms

High temperature catalytic oxidation (HTCO) was used for the first time to determine carbon content of heterotrophic protists (the helioflagellate Pteridomonas danica, the dinoflagellate Oxyrrhis marina, and the scuticociliate Uronema sp.) and bacteria (Escherichia coli). This technique has the advantage, over the conventional CHN analysis of glass-fiber filters, of measuring total organic carbon in the liquid phase. Failing to retain small organisms on filters and cell rupture during filtration can thus be avoided. Cell volumes were measured on live (Coulter Counter) and Lugol's iodine- or formaldehyde-preserved cells and used to obtain a carbon:biovolume conversion factor for each species. Carbon:biovolume conversion factors ranged from 123 to 175 and from 121 to 864 fg C mu m super(-3) for live and preserved cells, respectively. A linear regression of cell carbon content versus live biovolume gave a mean carbon:biovolume conversion factor of 125.3 plus or minus 7.6 (SE) fg C mu m super(-3) for the 4 species studied with biovolumes ranging from 0.69 to 1590 mu m super(3). The data obtained in this study is compared to live and preserved cells data obtained from the literature and the possibility of using a single carbon:biovolume conversion factor for bacteria and protozoa is discussed.