Eaton Daniel S, Crosson Sean, Fiebig Aretha
Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, Illinois, USA.
Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, Illinois, USA Department of Microbiology, University of Chicago, Chicago, Illinois, USA.
J Bacteriol. 2016 Sep 9;198(19):2631-42. doi: 10.1128/JB.00027-16. Print 2016 Oct 1.
Growth in a surface-attached bacterial community, or biofilm, confers a number of advantages. However, as a biofilm matures, high-density growth imposes stresses on individual cells, and it can become less advantageous for progeny to remain in the community. Thus, bacteria employ a variety of mechanisms to control attachment to and dispersal from surfaces in response to the state of the environment. The freshwater oligotroph Caulobacter crescentus can elaborate a polysaccharide-rich polar organelle, known as the holdfast, which enables permanent surface attachment. Holdfast development is strongly inhibited by the small protein HfiA; mechanisms that control HfiA levels in the cell are not well understood. We have discovered a connection between the essential general protein chaperone, DnaK, and control of C. crescentus holdfast development. C. crescentus mutants partially or completely lacking the C-terminal substrate binding "lid" domain of DnaK exhibit enhanced bulk surface attachment. Partial or complete truncation of the DnaK lid domain increases the probability that any single cell will develop a holdfast by 3- to 10-fold. These results are consistent with the observation that steady-state levels of an HfiA fusion protein are significantly diminished in strains that lack the entire lid domain of DnaK. While dispensable for growth, the lid domain of C. crescentus DnaK is required for proper chaperone function, as evidenced by observed dysregulation of HfiA and holdfast development in strains expressing lidless DnaK mutants. We conclude that DnaK is an important molecular determinant of HfiA stability and surface adhesion control.
Regulatory control of cell adhesion ensures that bacterial cells can transition between free-living and surface-attached states. We define a role for the essential protein chaperone, DnaK, in the control of Caulobacter crescentus cell adhesion. C. crescentus surface adhesion is mediated by an envelope-attached organelle known as the holdfast. Holdfast development is tightly controlled by HfiA, a small protein inhibitor that directly interacts with a WecG/TagA-family glycosyltransferase required for holdfast biosynthesis. We demonstrate that the C-terminal lid domain of DnaK is not essential for growth but is necessary for proper control of HfiA levels in the cell and for control of holdfast adhesin development.
附着在表面的细菌群落即生物膜的生长具有诸多优势。然而，随着生物膜成熟，高密度生长会给单个细胞带来压力，并且子代留在群落中可能变得不那么有利。因此，细菌会采用多种机制来根据环境状态控制对表面的附着和从表面的分散。淡水贫营养菌新月柄杆菌能够形成一种富含多糖的极性细胞器，称为固着器，它能实现永久性表面附着。固着器的形成受到小蛋白HfiA的强烈抑制；控制细胞中HfiA水平的机制尚不清楚。我们发现了必需的通用蛋白伴侣DnaK与新月柄杆菌固着器形成控制之间的联系。部分或完全缺失DnaK C端底物结合“盖子”结构域的新月柄杆菌突变体表现出更强的整体表面附着能力。DnaK盖子结构域的部分或完全截短使任何单个细胞形成固着器的概率增加3至10倍。这些结果与以下观察结果一致：在缺乏DnaK整个盖子结构域的菌株中，HfiA融合蛋白的稳态水平显著降低。虽然对于生长不是必需的，但新月柄杆菌DnaK的盖子结构域对于正确的伴侣功能是必需的，这在表达无盖子DnaK突变体的菌株中HfiA失调和固着器形成受到影响中得到证明。我们得出结论，DnaK是HfiA稳定性和表面黏附控制的重要分子决定因素。
细胞黏附的调控确保细菌细胞能够在自由生活状态和表面附着状态之间转换。我们确定了必需蛋白伴侣DnaK在新月柄杆菌细胞黏附控制中的作用。新月柄杆菌的表面黏附由一种附着在包膜上的细胞器即固着器介导。固着器的形成受到HfiA的严格控制，HfiA是一种小蛋白抑制剂，它直接与固着器生物合成所需的WecG/TagA家族糖基转移酶相互作用。我们证明，DnaK的C端盖子结构域对于生长不是必需的，但对于细胞中HfiA水平的正确控制以及固着器黏附素的形成控制是必需的。
