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Roles of Two Shewanella oneidensis MR-1 Extracellular Endonucleases

机译：两种沙瓦氏沙瓦氏菌MR-1细胞外核酸内切酶的作用

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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.
机译：异化还原铁细菌沙瓦氏菌One-1能够利用细胞外DNA（eDNA）作为碳，磷和氮的唯一来源。此外，我们最近证明，在生物膜形成的所有阶段，拟南芥MR-1都需要eDNA作为结构成分。在这项研究中，我们表征了两种希瓦氏菌胞外核酸内切酶ExeS和ExeM的作用。尽管ExeS可能会分泌到培养基中，但预计ExeM仍与细胞包膜相关。 exeM和exeS在磷酸盐限制的条件下都高度表达。缺少exeS和/或exeM的突变体表现出降低的eDNA降解;然而，只有在缺乏exeM的突变体中，沙门氏菌MR-1才能利用DNA作为磷的唯一来源。两种核酸内切酶均不能缓解eDNA浓度升高的毒性作用。在静态条件下，exeM和/或exeS的缺失会显着影响oneidensis MR-1的生物膜形成，并且在静态生物膜形成过程中exeM和exeS的表达急剧增加。在流体动力学条件下，exeM的缺失会导致生物膜发生变化，该生物膜由致密堆积的结构组成，这些结构被厚厚的eDNA覆盖。基于这些结果，我们假设ExeS，尤其是S.oneidensis MR-1的ExeM的主要作用是在生物膜形成过程中降解eDNA作为基质成分，从而改善营养供应并实现分离。

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