The relationship between optical density and cell number
differs between species
To investigate the relationship between cell count (obtained from flow
cytometry) and OD600 -value (from spectrophotometry)
across all 23 strains, we used linear regression (Figure 1, all
R2 > 0.87, p < 0.01). We
found significant differences between species in the slope of this
relationship (ANOVA: F7,22 = 5.63, p = 0.0025; Figure
2). The average slope extracted from S. cerevisiae regressions
was significantly steeper than the slopes found in S. mikatae,S. jurei, S. arboricola , and S. uvarum (Tukey HSD, allp < 0.05). The random effect ‘strain’ was
non-significant and only explained 4% of the variation in the data
(Wald p = 0.81; Table S2).