All of the marine bacterioplankton-derived 16S ribosomal DNA sequences previously deposited in GenBankwere reanalyzed to determine the number of bacterial species in the oceanic surface waters. These sequenceshave been entered into the database since 1990. The rate of new additions reached a peak in 1999 andsubsequently leveled off, suggesting that much of the marine microbial species richness has been sampled.When the GenBank sequences were dereplicated by using 97% similarity as a cutoff, 1,117 unique ribotypeswere found. Of the unique sequences, 609 came from uncultured environmental clones and 508 came fromcultured bacteria. We conclude that the apparent bacterioplankton species richness is relatively low.
