Biomass composition and methods for the determination of metabolic reserve polymers in phototrophic sulfur bacteria

To study nutrient fluxes within aquatic ecosystems, the synthesis of biomass and of various storage polymers has been analysed in samples from a meromictic alpine lake. Methods are described for the quantitative determination of whole cell biomass, glycogen, polyhydroxyalkanoates (PHA) and sulfur. Methods were adapted to conditions present in natural environments and tested with samples from blooms of Chromatiaceae and with corresponding laboratory cultures. Dried bacterioplankton-biomass has been analyzed for sulfur, glycogen and polyhydroxyalkanoates, and after complete oxidation for SO₄^2-, NO₃^- and HPO₄^2-. The average elemental composition of biomass from phototrophic sulfur bacteria, depleted of sulfur and carbon storage compounds, was C₃₈₀H₅₈₀O₁₅₃N₆₇P₃S_2.5M, where M stands for the content of the remaining minor elements. C, H, O, N, P and S accounted for 86.7% of the total dry mass. Storage sulfur in natural populations was equivalent to 2.5% to 13.5% of the dry mass; its content varied by 80% within a diurnal cycle. Glycogen contents fluctuated by approximately 50%; they accounted for 7.5% to 15.2% of the dry cell mass. The total content of reserve materials per cell never exceeded 30% of the dry mass. PHA had not been found in appreciable amounts in cells harvested from the natural lake habitat. Under certain conditions in the laboratoryChromatium okenii could be induced, however, to produce polyhydroxyalkanoates. Sulfur, glycogen and PHA contents of 33, 26 and 11%, respectively, were achieved under laboratory-culture conditions. Cells with up to 60% of their dry mass consisting of reserve materials can be obtained under selected laboratory conditions.