Effect of the phospholipid regulator CrpO on salt tolerance. Anoxic phototrophic cultures of R. sphaeroides 2.4.1 containing the plasmids indicated were grown in the presence of added NaCl (0%, 1.5%, or 3%). Plasmids are as follows: ●, pBBR1MCS-2 (vector); ▴, pBBR-CrpO expressing crpO; and ■, pBBR-CrpO′ expressing truncated crpO, i.e., crpO′.