Cell cycle and physiological characteristics of Synechococcus (WH7803) in chemostat culture
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abstract
The marine cyanobacterium Synechococcus spp. is one of the most abundant picoplanktonic photoautotrophs in the world's oceans. When grown in nitrogen-limited chemostat culture under continuous light, Synechococcus strain WH7803 displays a bimodal DNA histogram. Consequently, the duration of each growth phase can be computed from the proportion of cells in each cell cycle phase. We measured cellular DNA distribution, carbon and nitrogen content, and pigment composition of Synechococcus WH7803 in a series of chemostat experiments with growth rate ranging from 0.1 to 0.9 d-1. Flow cytometric data showed that the duration of each cell cycle phase increased linearly with doubling time, and the fraction of cells in the S and G2 phases, f(S+G2), was relatively constant at growth rates of less than i doubling d-1. Cellular carbon and nitrogen contents were about 200 and 40 fg cell-1, respectively, but were much higher for slowly growing cells. The carbon to nitrogen ratio, the carbon to chlorophyll a ratio, and the ratio of zeaxanthin to chlorophyll a all decreased with increasing growth rate. These observed relationships are useful for applying cell cycle analysis to estimate growth rate, or for using cell abundance or pigment concentrations to estimate biomass and productivity of Synechococcus in the sea.
