Abstract
Cyanobacteria are among the few microbes that have the ability to grow in elevated pH. The cyanobacterial acclimation to high pH involves the upregulation of mechanisms targeting pH homeostasis (such as Na+/H+ antiporters) as well as a more general stress response e.g. production of chaperone or heat shock proteins that maintain cellular homeostasis. Previous analysis of the transcriptional response to high pH in the model cyanobacterium Synechocystis sp. PCC 6803 (hereafter, Synechocystis 6803) identified the genes slr1501 (hypothetical) and sll1392 (pfsR) as upregulated at high pH. This study investigated the roles of these genes in relation to high pH acclimation by making mutant strains lacking each of these genes. Experimental data indicates that neither slr1501 nor sll1392 are essential for acclimation to high pH. However, the application of multiple stressors (salt, high light, osmotic stress) did reveal growth phenotypes in the absence of slr1501. Results were consistent with a role for slr1501 in the negative regulation of Synechocystis 6803 growth under certain stressful environment conditions, including combinations of ionic, osmotic and high light stress. The gene sll1392 has been previously shown to have a role in the regulation of high light and iron deprivation response in Synechocystis 6803. In this study the response to high light and iron deprivation was found to be also dependent on the pH of the culture medium. Neither slr1501 nor sll1392 were required for growth at pH 7.5 or pH 10, however, both genes appear to be involved be in stress response and that the pH of culture medium can impact on this response. This research advances the understanding of the cellular mechanisms of acclimation to high pH and other environmental stresses in cyanobacteria.