FIG. 6.

In situ hybridization of natural Prochlorococcus population. (A) Flow cytometric signature of Prochlorococcus (with 0.474-mm-diameter latex beads) showing forward angle light scatter (related to size) versus red fluorescence (from chlorophyll). (B) Probe-conferred fluorescence of Prochlorococcus cells as defined from panel A, hybridized with positive probe (pEUB339), negative probe (pNEG1198), and no probe. Water was collected from the Pacific Ocean in an oligotrophic region off the California coast.