Vesicle size variation with changes in environmental factors. The measured vesicle diameters are shown for (A) Alteromonas macleodii MIT1002 across growth temperatures, (B) Prochlorococcus strains across growth temperatures, and (C) Prochlorococcus strains grown at different relative light irradiances. LL, low light; ML, medium light; HL, high light; VHL, very high light (Table S1). Asterisks indicate conditions that differ significantly from the overall strain mean diameter (Wilcoxon test; *, P ≤ 0.05; **, P ≤ 0.01; ***, P ≤ 0.001; ****, P ≤ 0.0001).