Liao Chengheng, Rigali Sébastien, Cassani Cuauhtemoc Licona, Marcellin Esteban, Nielsen Lars Keld, Ye Bang-Ce
Laboratory of Biosystems and Microanalysis, State Key Laboratory of Bioreactor Engineering, Shanghai Collaborative Innovation Center for Biomanufacturing Technology, East China University of Science and Technology, Shanghai 200237, PR China.
Centre for Protein Engineering, Institut de Chimie B6a, B-4000 Liège, Belgium.
Microbiology (Reading). 2014 Sep;160(Pt 9):1914-1928. doi: 10.1099/mic.0.078261-0. Epub 2014 Jul 9.
Chitin degradation and subsequent N-acetylglucosamine (GlcNAc) catabolism is thought to be a common trait of a large majority of actinomycetes. Utilization of aminosugars had been poorly investigated outside the model strain Streptomyces coelicolor A3(2), and we examined here the genetic setting of the erythromycin producer Saccharopolyspora erythraea for GlcNAc and chitin utilization, as well as the transcriptional control thereof. Sacch. erythraea efficiently utilize GlcNAc most likely via the phosphotransferase system (PTS(GlcNAc)); however, this strain is not able to grow when chitin or N,N'-diacetylchitobiose [(GlcNAc)2] is the sole nutrient source, despite a predicted extensive chitinolytic system (chi genes). The inability of Sacch. erythraea to utilize chitin and (GlcNAc)2 is probably because of the loss of genes encoding the DasABC transporter for (GlcNAc)2 import, and genes for intracellular degradation of (GlcNAc)2 by β-N-acetylglucosaminidases. Transcription analyses revealed that in Sacch. erythraea all putative chi and GlcNAc utilization genes are repressed by DasR, whereas in Strep. coelicolor DasR displayed either activating or repressing functions whether it targets genes involved in the polymer degradation or genes for GlcNAc dimer and monomer utilization, respectively. A transcriptomic analysis further showed that GlcNAc not only activates the transcription of GlcNAc catabolism genes but also activates chi gene expression, as opposed to the previously reported GlcNAc-mediated catabolite repression in Strep. coelicolor. Finally, synteny exploration revealed an identical genetic background for chitin utilization in other rare actinomycetes, which suggests that screening procedures that used only the chitin-based protocol for selective isolation of antibiotic-producing actinomycetes could have missed the isolation of many industrially promising strains.
几丁质降解以及随后的N-乙酰葡糖胺（GlcNAc）分解代谢被认为是绝大多数放线菌的共同特征。在模式菌株天蓝色链霉菌A3(2)之外，对氨基糖利用的研究较少，我们在此研究了红霉素产生菌糖多孢红霉菌中GlcNAc和几丁质利用的遗传背景及其转录调控。糖多孢红霉菌很可能通过磷酸转移酶系统（PTS(GlcNAc)）有效利用GlcNAc；然而，尽管预测有广泛的几丁质分解系统（chi基因），但当几丁质或N,N'-二乙酰壳二糖[（GlcNAc）2]作为唯一营养源时，该菌株无法生长。糖多孢红霉菌无法利用几丁质和（GlcNAc）2可能是因为编码用于（GlcNAc）2导入的DasABC转运蛋白的基因以及用于通过β-N-乙酰葡糖胺酶进行（GlcNAc）2细胞内降解的基因缺失。转录分析表明，在糖多孢红霉菌中，所有假定的chi和GlcNAc利用基因都受到DasR的抑制，而在天蓝色链霉菌中，DasR根据其靶向参与聚合物降解的基因还是分别靶向GlcNAc二聚体和单体利用的基因，表现出激活或抑制功能。转录组分析进一步表明，与之前报道的天蓝色链霉菌中GlcNAc介导的分解代谢物阻遏相反，GlcNAc不仅激活GlcNAc分解代谢基因的转录，还激活chi基因表达。最后，同线性探索揭示了其他稀有放线菌中几丁质利用的相同遗传背景，这表明仅使用基于几丁质的方案进行选择性分离产抗生素放线菌的筛选程序可能会错过许多具有工业前景的菌株的分离。
