Roles of Two Shewanella oneidensis MR-1 Extracellular Endonucleases
Roles of Two Shewanella oneidensis MR-1 Extracellular Endonucleases
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DOI：
10.1128/aem.00643-11
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发表时间：
2011-08-01
影响因子：
4.4
通讯作者：
Thormann, Kai M.
中科院分区：
文献类型：
--
作者：
Goedeke, Julia;Heun, Magnus;Thormann, Kai M.
异化铁还原菌Shewanella oneidensis MR-1能够利用胞外DNA（eDNA）作为碳、磷和氮的唯一来源。此外，我们最近证明了S。oneidensis MR-1在生物膜形成的所有阶段都需要eDNA作为结构组分。在这项研究中，我们的特点的两个希瓦氏菌胞外核酸内切酶，ExeS和ExeM的作用。虽然ExeS可能分泌到培养基中，但预计ExeM仍与细胞包膜结合。exeM和exeS都在磷酸盐限制条件下高度表达。缺乏exeS和/或exeM的突变体表现出降低的eDNA降解;然而，S. oneidensis MR-1利用DNA作为唯一磷源的能力仅在缺乏exeM的突变体中受到影响。这两种核酸内切酶都不能消除eDNA浓度增加的毒性作用。exeM和/或exeS的缺失显著影响S的生物膜形成。oneidensis MR-1在静态条件下表达，并且在静态生物膜形成期间exeM和exeS的表达急剧增加。在流体动力学条件下，exeM的缺失导致改变的生物膜，其由被厚层eDNA覆盖的密集堆积的结构组成。基于这些结果，我们假设，一个主要的作用，ExeS，特别是，ExeM的S。oneidensis MR-1的作用是在生物膜形成期间降解作为基质组分的eDNA，以改善营养供应并使其能够分离。
The dissimilatory iron-reducing bacterium Shewanella oneidensis MR-1 is capable of using extracellular DNA (eDNA) as the sole source of carbon, phosphorus, and nitrogen. In addition, we recently demonstrated that S. oneidensis MR-1 requires eDNA as a structural component during all stages of biofilm formation. In this study, we characterize the roles of two Shewanella extracellular endonucleases, ExeS and ExeM. While ExeS is likely secreted into the medium, ExeM is predicted to remain associated with the cell envelope. Both exeM and exeS are highly expressed under phosphate-limited conditions. Mutants lacking exeS and/or exeM exhibit decreased eDNA degradation; however, the capability of S. oneidensis MR-1 to use DNA as the sole source of phosphorus is only affected in mutants lacking exeM. Neither of the two endonucleases alleviates toxic effects of increased eDNA concentrations. The deletion of exeM and/or exeS significantly affects biofilm formation of S. oneidensis MR-1 under static conditions, and expression of exeM and exeS drastically increases during static biofilm formation. Under hydrodynamic conditions, a deletion of exeM leads to altered biofilms that consist of densely packed structures which are covered by a thick layer of eDNA. Based on these results, we hypothesize that a major role of ExeS and, in particular, ExeM of S. oneidensis MR-1, is to degrade eDNA as a matrix component during biofilm formation to improve nutrient supply and to enable detachment.