Mutations in ampG and Lytic Transglycosylase Genes Affect the Net Release of Peptidoglycan Monomers from Vibrio fischeri
Mutations in ampG and Lytic Transglycosylase Genes Affect the Net Release of Peptidoglycan Monomers from Vibrio fischeri
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DOI：
10.1128/jb.01547-08
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发表时间：
2009-04-01
影响因子：
3.2
通讯作者：
Stabb, Eric V.
中科院分区：
文献类型：
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作者：
Adin, Dawn M.;Engle, Jacquelyn T.;Stabb, Eric V.
光器官共生体费氏弧菌释放N-乙酰葡糖胺基-1，6-脱水-N-乙酰胞壁酰丙氨酰-γ-谷氨酰二氨基庚二酰丙氨酸，肽聚糖的二硫键四肽组分，在此称为“PG单体”。“相比之下，大多数革兰氏阴性细菌有效地回收PG单体，并且它不会在细胞外积累。PG单体可以刺激宿主鱿鱼Euprymna speakopes中正常的光器官形态发生，导致纤毛附属物的退化，类似于由V. fischeri感染引发的退化。我们研究了费氏弧菌PG单体的净释放是否是由于裂解性转糖基酶活性或AmpG缺陷所致，AmpG是PG单体进入细胞质进行再循环的渗透酶。ampG突变体显示净PG单体释放增加100倍，表明AmpG是功能性的。ampG突变也赋予了非特征性的能力，诱导轻器官形态发生，即使在放置在一个nonmotile flaJ突变，不能感染轻器官隐窝。我们针对五个潜在的裂解转糖基酶基因单独和特定的组合，以评估其在PG单体释放的作用。ltgA、ltgD和ltgY中的突变的组合降低了净PG单体释放，并且缺乏所有这三种基因的三重突变体在培养物上清液中几乎没有PG单体积累。这种突变体和野生型一样在宿主中定居;然而，受muclidae感染的鱿鱼更容易在后来被第二种V. fischeri菌株重复感染。我们建议，缺乏PG单体释放这种突变体的结果在较少的退化的感染促进纤毛附属物，导致这种倾向的重复感染。
The light-organ symbiont Vibrio fischeri releases N-acetylglucosaminyl-1,6-anhydro-N-acetylmuramylalanyl-gamma-glutamyldiaminopimelylalanine, a disaccharide-tetrapeptide component of peptidoglycan that is referred to here as "PG monomer." In contrast, most gram-negative bacteria recycle PG monomer efficiently, and it does not accumulate extracellularly. PG monomer can stimulate normal light-organ morphogenesis in the host squid Euprymna scolopes, resulting in regression of ciliated appendages similar to that triggered by infection with V. fischeri. We examined whether the net release of PG monomers by V. fischeri resulted from lytic transglycosylase activity or from defects in AmpG, the permease through which PG monomers enter the cytoplasm for recycling. An ampG mutant displayed a 100-fold increase in net PG monomer release, indicating that AmpG is functional. The ampG mutation also conferred the uncharacteristic ability to induce light-organ morphogenesis even when placed in a nonmotile flaJ mutant that cannot infect the light-organ crypts. We targeted five potential lytic transglycosylase genes singly and in specific combinations to assess their role in PG monomer release. Combinations of mutations in ltgA, ltgD, and ltgY decreased net PG monomer release, and a triple mutant lacking all three of these genes had little to no accumulation of PG monomers in culture supernatants. This mutant colonized the host as well as the wild type did; however, the mutant-infected squid were more prone to later superinfection by a second V. fischeri strain. We propose that the lack of PG monomer release by this mutant results in less regression of the infection-promoting ciliated appendages, leading to this propensity for superinfection.