CHARACTERIZATION OF NUCLEAR-DNA IN 12 SPECIES OF CHLORELLA (CHLOROCOCCALES, CHLOROPHYTA) BY DNA REASSOCIATION

Strains of 12 different species of the genus Chlorella were analyzed for amount, reiteration frequency and kinetic complexity of chromosomal DNA components by C0t analysis. The resulting C0t curves reveal at least two different DNA components consisting of single copy DNA (up to 95%) and of repetitive DNA with complexities of 4.1 × 103 base pairs (bp) to approximately 11.7 × 103 bp and a reiteration frequency of 100-760. The total amount of repetitive DNA is less than 9% of the nuclear genome and similar in all strains studied. In contrast, the total kinetic complexity varies in a wide range from 1.26 × 107 bp to 8.08 × 107 bp which is mainly due to differences in the size of single copy DNA. The genome sizes in Chlorella seem not to be correlated with biochemical and physiological characteristics and therefore are unlikely to be useful as a taxonomical marker. A comparison of thermal denaturation profiles showed that the melting points of repetitive and single copy DNA differ by approximately 7°C which may result from base mismatch and/or from a distinct base composition of the repetitive DNA. © 1990.