Using specific deoxyoligonucleotide probes we have discovered seasonal
ly strong (up to almost-equal-to 100%) dominance of bacteria hybridizi
ng to a single probe, in near shore waters off Scripps pier (32-degree
s 53' N; 117-degrees 15' W). The probes were designed from partially s
equenced 16S rRNA (V3 domain) of isolated marine bacteria. The results
indicate that this approach may be used for studies of bacterial popu
lations in the marine environment. We have shown that a number of geno
types that at times are dominant in the natural assemblages are cultur
able (and not, ''viable-but-unculturable'). Additionally, our data sug
gests that the discrepancy between viable counts and direct counts in
sea water samples can be explained by low plating efficiency.