Functional Specificity of Extracellular Nucleases of Shewanella oneidensis MR-1
Functional Specificity of Extracellular Nucleases of Shewanella oneidensis MR-1
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DOI：
10.1128/aem.07895-11
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发表时间：
2012-06-01
影响因子：
4.4
通讯作者：
Thormann, Kai M.
中科院分区：
文献类型：
--
作者：
Heun, Magnus;Binnenkade, Lucas;Thormann, Kai M.
像希瓦氏菌（Shewanella oneidensis） MR-1这样的细菌物种需要胞外核分解活性来利用细胞外DNA （eDNA）作为营养来源，并在生物膜形成过程中作为结构基质成分的eDNA进行周转。我们之前已经鉴定了两种s.o onedensis MR-1的细胞外核酸酶，ExeM和ExeS。虽然两者都参与生物膜的形成，但它们并不是利用eDNA作为营养物质所必需的。在这里，我们鉴定并表征了希瓦氏菌的第三种胞外核酸酶EndA。异种过量生产和纯化的蛋白质是高活性和快速降解各种来源的线性和超螺旋dna。功能需要二价金属离子（Mg2+或Mn2+）。endA与细胞外磷酸酶phoA共转录，在缺磷时不上调。endA的缺失既取消了s.o oneidensis MR-1对DNA的细胞外降解，也取消了将eDNA作为磷的唯一来源的能力。利用eDNA作为营养物，PhoA并不是严格要求的。在浮游生物生长过程中，EndA的活性阻止了大细胞聚集体的形成。然而，与ExeM的结果相反，endA的缺失对生物膜的形成只有轻微的影响。研究结果表明，在不同的条件下，蛇麻草的胞外核酸酶发挥着特定的功能。
Bacterial species such as Shewanella oneidensis MR-1 require extracellular nucleolytic activity for the utilization of extracellular DNA (eDNA) as a source of nutrients and for the turnover of eDNA as a structural matrix component during biofilm formation. We have previously characterized two extracellular nucleases of S. oneidensis MR-1, ExeM and ExeS. Although both are involved in biofilm formation, they are not specifically required for the utilization of eDNA as a nutrient. Here we identified and characterized EndA, a third extracellular nuclease of Shewanella. The heterologously overproduced and purified protein was highly active and rapidly degraded linear and supercoiled DNAs of various origins. Divalent metal ions (Mg2+ or Mn2+) were required for function. endA is cotranscribed with phoA, an extracellular phosphatase, and is not upregulated upon phosphostarvation. Deletion of endA abolished both extracellular degradation of DNA by S. oneidensis MR-1 and the ability to use eDNA as a sole source of phosphorus. PhoA is not strictly required for the exploitation of eDNA as a nutrient. The activity of EndA prevents the formation of large cell aggregates during planktonic growth. However, in contrast to the findings for ExeM, endA deletion had only minor effects on biofilm formation. The findings strongly suggest that the extracellular nucleases of S. oneidensis exert specific functions required under different conditions.