Distinct salt-dependent effects impair Fremyella diplosiphon pigmentation and cellular shape

Salt impairs cellular morphology and photosynthetic pigment accumulation in the cyanobacterium Fremyella diplosiphon. Recent findings indicated that the impact of salt on cellular morphology was attributable to salt-associated effects on osmotic regulation, as the impact on morphology was reversible when cells were treated with an osmoticum in the presence of salt. The impact of salt on photosynthetic pigment accumulation was associated with ionic effects of salt on the cells, as pigment levels remained low when salt-treated cells were incubated together with an osmoticum or an antioxidant, the latter to mitigate the impact of a salt-associated accumulation of reactive oxygen species. Here, we provide evidence that the transcripts for genes encoding the phycobiliproteins are not reduced in the presence of salt. These results suggest that the negative impact of salt-mediated changes on pigment accumulation occurs post-transcriptionally. A greater understanding of the mechanisms which impact growth of strains such as F. diplosiphon, which harbor pigments that allow low-light and shade-tolerated growth, may facilitate the development or adaptation of such strains as useful for remediation of salt-impacted soils or biofuel production.