High degree of genetic variation in Prochlorococcus (Prochlorophyta) revealed by RFLP analysis

A genetic characterization of nine strains of Prochlorococcus originating from various depths of the Mediterranean Sea, the Sargasso Sea, the North and the tropical Atlantic Ocean and the Pacific Ocean was performed by restriction fragment length polymorphism (RFLP) mapping using probes for rbcL, rbcS, psbA and woxA. This study revealed extensive genetic variation among strains, which were grouped into two distinct clusters. Unexpectedly, with one exception (TATL1 strain), the strains clustered by isolation depth (i.e. near surface versus deep isolates) rather than by geographic origin. These relationships were confirmed by secondary RFLP analysis of psbA amplification products using Prochlorococcus-specific polymerase chain reaction (PCR) primers