A small and compact genome in the marine cyanobacterium Prochlorococcus marinus CCMP 1375: lack of an intron in the gene for tRNA(Leu)(UAA) and a single copy of the rRNA operon

Data obtained by pulsed field gel electrophoresis revealed for Prochlorococ cus marinus CCMP 1375 a genome size of 1.81 +/- 0.04 Mbp. This value is sig nificantly smaller than for all other cyanobacteria investigated so far. Th e absence of an intron in the gene for tRNA(Leu)(UAA), which otherwise is w idespread among cyanobacteria, and the additional finding that the ribosoma l operon exists as a single copy suggest that the deletion of non-essential sequences played a major role in the evolution of P. marinus. A small geno me may have been advantageous in the adaptation to very oligotrophic marine conditions. (C) 1999 Federation of European Microbiological Societies. Pub lished by Elsevier Science B.V. All rights reserved.