Die1 patterns of cell division in marine Synechococcus spp. (Cyanobacteria): use of the frequency of dividing cells technique to measure growth rate*

Natural populations of the planktonic cyanobacteria Synechococcus spp. exhibit a diel pattern in the frequency of dividing cells (FDC). Based on this observation, we tested the applicability of the FDC technique for estimating growth rate of a population grown on a IighWdark cycle. In laboratory experiments, the phycoerythrin-containing strains WH7803, WH8012, WH8107, and WH8108 were grown under various light and temperature conditions and the duration of division, td, a parameter necessary for the calculation of growth rate, was determined to be 3 h. Using this td value, growth rates of oceanic populations exhibiting diel patterns in FDC were found to range from 0.42 to 0.86 d-l, and these values exceed previous estimates of phytoplankton growth rates in oligotrophic regions. In experiments conducted at a Sargasso Sea station, growth rates calculated by the FDC technique were in close agreement with calculated instantaneous growth rates. In all cases, growth rates were higher for samplesincubated at surface light intensities than at 1 % surface light intensities. Using this technique under appropriate conditions, strain-specific growth rates can be determined.