The type VI secretion system (T6SS) is a widespread antibacterial weapon capable of secreting multiple effectors for inhibition of competitor cells. Most of the effectors in the system share the same purpose of target intoxication, but the rationale for maintaining various types of effectors in a species is not well studied. In this study, we showed that a peptidoglycan amidase effector in Agrobacterium tumefaciens, Tae, cleaves d-Ala-meso-diaminopimelic acid (mDAP) and d-Glu bonds in peptidoglycan and is able to suppress the growth of Escherichia coli recipient cells. The growth suppression was effective only under the condition in which E. coli cells are actively growing. In contrast, the Tde DNase effectors in the strain possessed a dominant killing effect under carbon starvation. Microscopic analysis showed that Tde triggers cell elongation and DNA degradation, while Tae causes cell enlargement without DNA damage in E. coli recipient cells. In a rich medium, A. tumefaciens harboring only functional Tae was able to maintain competitiveness among E. coli and its own sibling cells. Growth suppression and the competitive advantage of A. tumefaciens were abrogated when recipient cells produced the Tae-specific immunity protein Tai. Given that Tae is highly conserved among A. tumefaciens strains, the combination of Tae and Tde effectors could allow A. tumefaciens to better compete with various competitors by increasing its survival during changing environmental conditions.

中文翻译：

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根癌农杆菌采用通用的抗菌策略以提高其竞争力

VI型分泌系统（T6SS）是一种广泛的抗菌武器，能够分泌多种效应物来抑制竞争细胞。系统中的大多数效应子具有共同的目标中毒目的，但是在物种中维持各种类型效应子的基本原理尚未得到很好的研究。在这项研究中，我们发现，肽聚糖酰胺酶的效应在根癌土壤杆菌，跆拳道，裂解d -Ala-内消旋二氨基庚二酸（MDAP）和ð在肽聚糖-Glu键和能够抑制生长的大肠杆菌的受体细胞。仅在大肠杆菌条件下，生长抑制才有效细胞正在活跃地增长。相反，该菌株中的Tde DNase效应子在碳饥饿下具有主要的杀伤作用。显微镜分析表明，Tde引发细胞伸长和DNA降解，而Tae引起细胞扩增而在大肠杆菌受体细胞中没有DNA损伤。在丰富的培养基中，仅含有功能性Tae的根癌农杆菌能够维持大肠杆菌及其同胞的竞争能力。当受体细胞产生Tae特异性免疫蛋白Tai时，废除根癌农杆菌的生长抑制和竞争优势。鉴于Tae在根癌农杆菌菌株中高度保守，因此Tae和Tde效应子的组合可以允许根癌农杆菌通过在不断变化的环境条件下提高生存能力，从而更好地与各种竞争者竞争。