Microbial enrichment and gene functional categories revealed on the walls of a spent fuel pool of a nuclear power plant

Microorganisms developing in the liner of the spent fuel pool (SFP) and the fuel transfer channel (FTC) of a Nuclear Power Plant (NPP) can form high radiation resistant biofilms and cause corrosion. Due to difficulties and limitations to obtain large samples from SFP and FTC, cotton swabs were used to collect the biofilm from the wall of these installations. Molecular characterization was performed using massively parallel sequencing to obtain a taxonomic and functional gene classification. Also, samples from the drainage system were evaluated because microorganisms may travel over the 12-meter column of the pool water of the Brazilian Nuclear Power Plant (Angra1), which has been functioning since 1985. Regardless of the treatment of the pool water, our data reveal the unexpected presence of Fungi (Basidiomycota and Ascomycota) as the main contaminators of the SFP and FTC. Ustilaginomycetes (Basidiomycota) was the major class contributor (70%) in the SFP and FTC reflecting the little diversity in these sites; nevertheless, Proteobacteria, Actinobacteria, Firmicutes (Bacilli) were present in small proportions. Mapping total reads against six fungal reference genomes indicate that there is, in fact, a high abundance of fungal sequences in samples collected from SFP and FTC. Analysis of the ribosomal internal transcribed spacer (ITS) 1 and 2 regions and the protein found in the mitochondria of eukaryotic cells, cytochrome b (cytb) grouped our sample fungi in the clade 7 as Ustilago and Pseudozyma. In contrast, in the drainage system, Alphaproteobacteria were present in high abundances (55%). The presence of Sphingopyxis, Mesorhizobium, Erythrobacter, Sphingomonas, Novosphingobium, Sphingobium, Chelativorans, Oceanicaulis, Acidovorax, and Cyanobacteria was observed. Based on genomic annotation data, the assessment of the biological function found a higher proportion of protein-coding sequences related to respiration and protein metabolism in SFP and FTC samples. The knowledge of this biological inventory present in the system may contribute to further studies of potential microorganisms that might be useful for bioremediation of nuclear waste.核电站（Nuclear Power Plant, NPP）的乏燃料池（Spent Fuel Pool, SFP）与燃料转运通道（Fuel Transfer Channel, FTC）衬里中滋生的微生物，可形成高抗辐射生物膜并引发腐蚀。由于从SFP和FTC获取大体积样本存在难度与局限性，研究人员采用棉拭子从上述设施的壁面采集生物膜样本。通过大规模平行测序开展分子表征，以获得分类学与功能基因分类数据。此外，研究还对排水系统的样本进行了评估，因为微生物可能会在这座自1985年起投入运行的巴西核电站（Angra1）的12米水池水柱中迁移。无论池水采用何种处理方式，我们的数据均显示，真菌（担子菌门Basidiomycota、子囊菌门Ascomycota）作为SFP与FTC的主要污染物，其存在出乎预料。黑粉菌纲（Ustilaginomycetes，属于担子菌门Basidiomycota）是SFP与FTC中的优势类群，占比达70%，反映出这些位点的微生物多样性极低；不过变形菌门、放线菌门、厚壁菌门（芽孢杆菌纲Bacilli）仅占少量比例。将总reads比对至6个真菌参考基因组的结果表明，SFP和FTC采集的样本中确实存在丰度极高的真菌序列。对核糖体内部转录间隔区（ribosomal internal transcribed spacer, ITS）1和2区域，以及真核细胞线粒体细胞色素b（cytochrome b, cytb）蛋白的分析，将本次研究样本中的真菌归类为黑粉菌属（Ustilago）与假丝酵母属（Pseudozyma）所属的第7进化支。与之相反，排水系统的样本以α-变形菌纲（Alphaproteobacteria）占比最高（55%）。研究还观察到鞘氨醇单胞菌属（Sphingopyxis）、中慢生根瘤菌属（Mesorhizobium）、赤杆菌属（Erythrobacter）、鞘氨醇单胞菌属（Sphingomonas）、新鞘氨醇杆菌属（Novosphingobium）、鞘氨醇杆菌属（Sphingobium）、螯合杆菌属（Chelativorans）、海洋杆菌属（Oceanicaulis）、食酸菌属（Acidovorax）以及蓝细菌门（Cyanobacteria）的存在。基于基因组注释数据，对生物学功能的分析显示，SFP与FTC样本中与呼吸作用及蛋白质代谢相关的蛋白质编码序列占比更高。对该系统中存在的生物群落的认知，可为后续研究潜在的、可用于核废料生物修复的微生物提供参考。