Dynamics of Prochlorococcus transcriptome changes during the transition from the expected dark period into extended darkness. Dynamics of Prochlorococcus transcriptome changes during the transition from the expected dark period into extended darkness. Values depict the number of significantly differentially abundant transcripts at each time point in either axenic (orange) or cocultured (blue) Prochlorococcus cultures which were kept in the dark compared to the corresponding control cultures that remained under a 13:11 diel L:D cycle. Under the unperturbed light cycle, sunrise would have occurred at the 35-h time point (indicated with a black vertical dashed line); the 28- and 32-h time points represent times during the “expected night” period, prior to the shift into extended darkness, and serve as a control. Transcripts significantly enriched in the “extended darkness” cultures are represented by bars above the center line, with depleted transcripts below the center line; the bars at 28 and 32 h are too small to see at this scale. The number of enriched or depleted transcripts are indicated in black numbers; transcripts common to both axenic and cocultures are noted by white dashed lines and numbers. Steven J. Biller et al. mSystems 2018; doi:10.1128/mSystems.00040-18