The iron-regulated isiA gene of Fischerella muscicola strain PCC 73103 is linked to a likewise regulated gene encoding a Pcb-like chlorophyll-binding protein

Abstract

The expression of the chlorophyll a-binding, iron stress-induced protein IsiA is part of the cyanobacterial response to iron deficiency. A new isiA gene from the filamentous heterocystous cyanobacterial strain, Fischerella muscicola PCC 73103, was identified using standard and inverse PCR. While in unicellular cyanobacterial strains isiA is organized in an operon with isiB (encoding flavodoxin), in Fischerella not an isiB gene but another chlorophyll-binding protein encoding gene was identified downstream of isiA, which shows significant similarities to Pcb-like protein encoding genes known from prochlorophytes. The expression of both genes was clearly activated under iron deficiency. Although isiA and pcbC were independently transcribed, the size of the pcbC transcript indicates a large iron-regulated operon. Beside a 10fold increase of isiA transcript content iron-starved cells of Fischerella showed a blue-shift in the red chlorophyll a absorption peak. In addition, chlorophyll fluorescence at 77 K was dominated by an emission peak at 685 nm. These features are in accordance with the characteristics of IsiA accumulation in iron-starved unicellular cyanobacteria, suggesting identical IsiA function in heterocystous strains in spite of different genetic organization. ß

Insights into the Physiology and Ecology of the Brackish-Water-Adapted Cyanobacterium Nodularia spumigena CCY9414 Based on a Genome-Transcriptome Analysis

“…In between the flavodoxin and isiA genes a protein of unknown function with an alpha/beta hydrolase domain is encoded ( nsp37480 ), homologs of which are associated with flavodoxin genes also in most other N2-fixing cyanobacteria. A similar situation with several tightly clustered genes of the IsiA/CP43 family exists in Anabaena PCC 7120 and other filamentous, N2-fixing cyanobacteria such as Fischerella muscicola PCC 73103 [68]. A phylogenetic analysis of these proteins shows that one of the proteins from this family ( nsp37460 ) clusters with several well characterized IsiA proteins and hence is a distinct IsiA homolog.…”

“…Such an antenna complex may be a particularly efficient form of light-harvesting by PSI in the ecological niche of N. spumigena . The regulation of these genes in N. spumigena is not known, but at least for F. muscicola PCC 73103 the iron-stress-regulation of a comparable large operon with Pcb/PsbC homologs was detected [68].…”