Survival and growth of Spirulina platensis cells and thermodynamic stability of their main proteins after recultivation following irradiation with Cs137 γ doses of 0 to 400 kGy

Abstract

Using the optical and DSC studies, for the first time, it was shown that Spirulina platensis irradiated with Cs137 γ 400 kGy and then stored under anaerobic conditions in dark at 4 °C remained viable despite 96.9 % denaturation of its whole biomass. After preliminary irradiation with Cs137 γ 10 kGy to 400 kGy doses, the recultivated Spirulina platensis suspension restored its biomass, the cell growth increased by 10 %, chlorophyll increased by 27 %, and the phycobilisome complexes (PBPc) increased by 17 % compared to the normal values. The DSC data showed that PBSc in the recultivated samples, which were preliminarily irradiated with 10–400 kGy doses, melted cooperatively with the following parameters: ∆Hm = 39.39 J/g, Tm = 57.5 ± 0.3 °C, and ∆T = 3.3 ± 0.5 °C. These values were close to the freshly cultivated Spirulina platensis parameters. The PBPc weight percent of the total dry biomass W/W% calculated from the DSC data equaled 59.3 %. We demonstrated that storing native/fresh and/or recultivated Spirulina platensis under conditions close to ones under which it was irradiated caused a decrease in W/W% PBPc in a time-dependent manner, and a sharp increase in proteins that melt within the temperature range of 75–100 °C. We suggested that the observed redistribution of the biomass was caused by blockage of the light-harvesting proteins and initiation of the dark protein synthesis.