Sll0751 and Sll1041 are involved in acid stress tolerance in Synechocystis sp PCC 6803

The ATP-binding cassette (ABC) transporter is a multi-subunit membrane protein complex involved in lipid transport and acid stress tolerance in the cyanobacterium Synechocystis sp. PCC 6803. This organism has two sets of three ABC transporter subunits: Slr1045 and Slr1344, Sll0751 and Sll1002, and Sll1001 and Sll1041. We previously found that Slr1045 is essential for survival under acid stress condition (Tahara et al. 2012). In the present study, we examined the participation of other ABC transporter subunits in acid stress tolerance using a deletion mutant series of Synechocystis sp. PCC 6803. Although Slr1344 is highly homologous to Slr1045, Delta slr1344 cells were not susceptible to acid stress. Delta sll0751 and Delta sll1041 cells displayed acid stress sensitivity, whereas Delta sll1001/sll1002 double mutant cells grew normally. Under high- and low-temperature stress conditions, the growth rate of Delta slr1344 and Delta sll1001/sll1002 cells did not differ from WT cells, whereas Delta sll0751 and Delta sll1041 cells showed significant growth retardation, as previously observed in Delta slr1045 cells. Moreover, nile red staining showed more lipid accumulation in Delta slr1045, Delta sll0751, and Delta sll1041 cells than in WT cells. These results suggest that Slr1045, Sll0751, and Sll1041 function together as a lipid transport complex in Synechocystis sp. PCC 6803 and are essential for growth under various stresses.