Radiation Tolerance of Pseudanabaena catenata, a Cyanobacterium Relevant to the First Generation Magnox Storage Pond

Abstract

Recently a species of Pseudanabaena was identified as the dominant photosynthetic organism during a bloom event in a high pH (pH ∼11.4), radioactive spent nuclear fuel pond (SNFP) at the Sellafield Ltd., United Kingdom facility. The metabolic response of a laboratory culture containing the cyanobacterium Pseudanabaena catenata, a relative of the major photosynthetic microorganism found in the SNFP, to X-ray irradiation was studied to identify potential survival strategies used to support colonization of radioactive environments. Growth was monitored and the metabolic fingerprints of the cultures, during irradiation and throughout the post-irradiation recovery period, were determined using Fourier transform infrared (FT-IR) spectroscopy. A dose of 95 Gy delivered over 5 days did not significantly affect growth of P. catenata, as determined by turbidity measurements and cell counts. Multivariate statistical analysis of the FT-IR spectral data revealed metabolic variation during the post-irradiation recovery period, with increased polysaccharide and decreased amide spectral intensities. Increases in polysaccharides were confirmed by complementary analytical methods including total carbohydrate assays and calcofluor white staining. This observed increased production of polysaccharides is of significance, since this could have an impact on the fate of the radionuclide inventory in the pond via biosorption of cationic radionuclides, and may also impact on downstream processes through biofilm formation and biofouling.

Biomineralization of Sr by the Cyanobacterium Pseudanabaena catenata Under Alkaline Conditions

“…A photosynthetic culture dominated by P. catenata, which is a close match to the species identified in the FGMSP, was obtained from the NIVA Culture Collection of Algae (NIVA-CYA 152), Norway. Whilst it was not possible to source an axenic culture, previous 16S rRNA gene sequencing revealed that of the nine operational taxonomic units identified in the NIVA-CYA 152 culture, five were affiliated with genera identified in the FGMSP (Foster et al, 2020b). The P. catenata culture used in the current work was therefore considered representative of the pond community.…”

“…The growth of the P. catenata culture was assessed by measuring optical density at 600 nm (OD 600nm ) to indicate the total biomass present in the cultures. The concentration of Chl-a was determined using the same samples as used for the OD 600nm measurements, as described in Foster et al (2020b). Briefly, the cells from a 1 ml sample were pelleted by centrifuging at 14,000g for 10 min and the supernatant was discarded.…”

“…In order to image any Sr minerals formed during the experiment and their potential interactions with P. catenata [and other associated microorganisms present in the culture, since a nonaxenic culture could not be sourced (Foster et al, 2020b)] electron microscopy was carried out on non-fixed samples. Samples (1 ml) were taken after 20 days of incubation for analysis by TEM.…”

“…Despite its presence in a range of other environments and in algal blooms (Acinas et al, 2009;Zhu et al, 2015), there is little information in the scientific literature about the ecology of this filamentous cyanobacterium. Recently the response of a Pseudanabaena catenata culture, shown to be a close relative of the cyanobacterium in the pond, to ionizing radiation was documented (Foster et al, 2020b). The culture continued to grow when subjected to a total of 95 Gy over a 5 days period and showed elevated polysaccharide production as a result of the treatment.…”

“…While Sr is present in pond waters at low levels, 90 Sr is present at significant levels by activity (average of 160 Bq ml −1 during the sampling campaign reported in Foster et al, 2020a) and is potentially very soluble, and thus needs to be considered carefully during effluent processing to minimize discharges to the environment (Ashworth et al, 2018). The purpose of this investigation was to determine the fate of Sr in the presence of microorganisms representative of those in the FGMSP system, namely a mixed laboratory culture dominated by P. catenata, a good model for the pond community since it is a close relative to the cyanobacterium identified in the FGMSP (Foster et al, 2020b). This study also aimed to determine whether under the conditions of study, intracellular Sr-containing minerals could be formed by this species of cyanobacterium.…”