Fig. 2. Concentrations of intracellular and extracellular vitamin B₁₂ normalized to cell counts in Ruegeria pomeroyi cultures grown without an exogenous B₁₂ source across three temperature treatments.

R. pomeroyi cultures in early stationary phase were harvested for cyanocobalamin (B₁₂) measurements by mass spectrometry. Measured values were normalized to the number of cells in the originating culture volume (i.e., the number of cells in a cell pellet or the number of cells removed from a supernatant). Horizontal marks represent the mean B₁₂ concentration per cell for each treatment; vertical error bars are one standard deviation of the mean; open circles are individual data points. Pelleted cells contained significantly more B₁₂ than was present in supernatants (p < 0.05, t-test). While not a statistically significant difference, cells grown in the mid and hot-temperature treatments tended to have higher intracellular vitamin B₁₂ concentrations than cells grown in the cool-temperature treatment.