Which answer most closely represents the number of hours a decrease in optical density was observed during the seawater conditions?
The bacterial strain SN2 (Alteromonas naphthalenivorans) is known to contaminate both tidal flats and seawater. The graphs in Figure 1 show the results of an experiment intended to measure the cell growth of SN2 in a tidal flat environment with added Naphthalene (TF-N) and a tidal flat environment with added Pyruvate (TF-P). The concentration of Naphthalene and Pyruvate were also measured within this experiment. Additionally, changes in the optical density of seawater was measured when both Naphthalene and Pyruvate were added. The goal of this experiment was to better understand the Eco physiological behavior of SN2 in contaminated environments. The graphs in Figure 2 depict levels of correlation in level of gene expression between conditions.
Figures adapted from Genome-wide transcriptional responses of Alteromonas naphthalenivorans SN2 to contaminated seawater and marine tidal flat sediment by Hyun mi Jin et al.
(B) A decrease in optical density was observed during approximately 4 hours of incubation in the seawater conditions. Consider only the bottom graph of Figure 1. There is no observable decrease in SW-P during any time interval, but SW-N clearly decreases in optical density around the 16-hour mark. This continues for the remainder of the graph. Though the exact amount of time of decrease is unclear, the best answer available is 4 hours.