NUCLEIC-ACID CONTENT OF SYNECHOCOCCUS SPP. DURING GROWTH IN CONTINUOUS LIGHT AND LIGHT DARK CYCLES/

Light-limited batch cultures of Synechococcus spp. strains PCC 6301 an d WH 8103 exhibited a positive correlation between the specific growth rate and the cellular content of both RNA and DNA. The ratio of RNA t o DNA increased with the growth rate in Synechococcus sp. strain WH 81 03, as it does in heterotrophic bacteria, but remained constant in Syn echococcus sp, strain PCC 6301. The cellular content of nucleic acids decreased during light periods and increased during dark periods in Sy nechococcus sp, strain PCC 6301 entrained by 12-h light/12-h dark (diu rnal) cycles. This result was unexpected in light of experiments demon strating a circadian increase in transcriptional activity during the s ubjective light periods and a decrease in transcriptional activity dur ing subjective dark periods. The cyclical variation in cellular nuclei c acid content during diurnal cycles appears to be in part a function of the timing of cell division and will influence estimates of in situ growth rates or relative abundances of cyanobacteria using oligonucle otide probes complementary to 16S rRNA.