Diurnal Rhythms Result in Significant Changes in the Cellular Protein Complement in the Cyanobacterium Cyanothece 51142

Cyanothece sp. ATCC 51142 is a diazotrophic cyanobacterium notable for its ability to perform oxygenic photosynthesis and dinitrogen fixation in the same single cell. Previous transcriptional analysis revealed that the existence of these incompatible cellular processes largely depends on tightly synchronized expression programs involving ∼30% of genes in the genome. To expand upon current knowledge, we have utilized sensitive proteomic approaches to examine the impact of diurnal rhythms on the protein complement in Cyanothece 51142. We found that 250 proteins accounting for ∼5% of the predicted ORFs from the Cyanothece 51142 genome and 20% of proteins detected under alternating light/dark conditions exhibited periodic oscillations in their abundances. Our results suggest that altered enzyme activities at different phases during the diurnal cycle can be attributed to changes in the abundance of related proteins and key compounds. The integration of global proteomics and transcriptomic data further revealed that post-transcriptional events are important for temporal regulation of processes such as photosynthesis in Cyanothece 51142. This analysis is the first comprehensive report on global quantitative proteomics in a unicellular diazotrophic cyanobacterium and uncovers novel findings about diurnal rhythms.Cyanothece sp. ATCC 51142是一种固氮蓝细菌（diazotrophic cyanobacterium），其独特特征为可在单个细胞内同时完成产氧光合作用与生物固氮作用。既往转录组分析显示，这两种相互拮抗的细胞过程的共存，高度依赖于基因组中约30%基因参与的紧密同步化表达程序。为拓展现有研究认知，本研究采用高灵敏度蛋白质组学方法，探究昼夜节律对Cyanothece 51142蛋白质组的影响。本研究发现，250种蛋白质（占Cyanothece 51142基因组预测开放阅读框（Open Reading Frames, ORFs）的约5%），以及明暗交替培养条件下检测到的20%的蛋白质，其丰度呈现周期性振荡。研究结果表明，昼夜周期不同阶段的酶活性变化，可归因于相关蛋白质与关键化合物的丰度改变。全局蛋白质组学与转录组学数据的整合分析进一步揭示，转录后调控事件对于Cyanothece 51142中光合作用等过程的时序调控至关重要。本项蛋白质组分析是首个针对单细胞固氮蓝细菌的全局定量蛋白质组学综合报道，并揭示了有关昼夜节律的全新研究发现。