Active Fe-containing superoxide dismutase and abundant sodF mRNA in Nostoccommune (cyanobacteria) after years of desiccation

Active Fe-superoxide dismutase (SodF) was the third most abundant soluble p rotein in cells of Nostoc commune CHEN/1986 after prolonged (13 years) stor age in the desiccated state. Upon rehydration, Fe-containing superoxide dis umutase (Fe-SOD) was released and the activity was distributed between rehy drating cells and the extracellular fluid. The 21-kDa Fe-SOD polypeptide wa s purified, the N terminus was sequenced, and the data were used to isolate sodF from the clonal isolate N, commune DRH1, sodF encodes an open reading frame of 200 codons and is expressed as a monocistronic transcript (of app roximately 750 bases) from a region of the genome which includes genes invo lved in nucleic acid synthesis and repair, including dipyrimidine photolyas e (phr) and cytidylate monophosphate kinase (panC). sodF mRNA was abundant and stable in cells after long-term desiccation. Upon rehydration of desicc ated cells, there was a turnover of sodF mRNA within 15 min and then a rise in the mRNA pool to control levels (quantity of sodF mRNA in cells in late logarithmic phase of growth) over approximately 24 h. The extensive extrac ellular polysaccharide (glycan) of N. commune DRH1 generated superoxide rad icals upon exposure to W-A or -B irradiation, and these were scavenged by S OD, Despite demonstrated roles for the glycan in the desiccation tolerance of N, commune, it may in fact be a significant source of damaging free radi cals in vivo. It is proposed that the high levels of SodF in N. commune, an d release of the enzyme from dried cells upon rehydration, counter the effe cts of oxidative stress imposed by multiple cycles of desiccation and rehyd ration during W-A or -B irradiation in situ.