Murray S R, Bermudes D, de Felipe K S, Low K B
Department of Biology, Yale University, New Haven, Connecticut 06520, USA.
J Bacteriol. 2001 Oct;183(19):5554-61. doi: 10.1128/JB.183.19.5554-5561.2001.
Lipid A, a potent endotoxin which can cause septic shock, anchors lipopolysaccharide (LPS) into the outer leaflet of the outer membrane of gram-negative bacteria. MsbB acylates (KDO)(2)-(lauroyl)-lipid IV-A with myristate during lipid A biosynthesis. Reports of knockouts of the msbB gene describe effects on virulence but describe no evidence of growth defects in Escherichia coli K-12 or Salmonella. Our data confirm the general lack of growth defects in msbB E. coli K-12. In contrast, msbB Salmonella enterica serovar Typhimurium exhibits marked sensitivity to galactose-MacConkey and 6 mM EGTA media. At 37 degrees C in Luria-Bertani (LB) broth, msbB Salmonella cells elongate, form bulges, and grow slowly. msbB Salmonella grow well on LB-no salt (LB-0) agar; however, under specific shaking conditions in LB-0 broth, many msbB Salmonella cells lyse during exponential growth and a fraction of the cells form filaments. msbB Salmonella grow with a near-wild-type growth rate in MSB (LB-0 containing Mg(2+) and Ca(2+)) broth (23 to 42 degrees C). Extragenic compensatory mutations, which partially suppress the growth defects, spontaneously occur at high frequency, and mutants can be isolated on media selective for faster growing derivatives. One of the suppressor mutations maps at 19.8 centisomes and is a recessive IS10 insertional mutation in somA, a gene of unknown function which corresponds to ybjX in E. coli. In addition, random Tn10 mutagenesis carried out in an unsuppressed msbB strain produced a set of Tn10 inserts, not in msbB or somA, that correlate with different suppressor phenotypes. Thus, insertional mutations, in somA and other genes, can suppress the msbB phenotype.
脂多糖A是一种能引发败血性休克的强效内毒素，它将脂多糖（LPS）锚定在革兰氏阴性菌外膜的外小叶中。在脂多糖A生物合成过程中，MsbB会用肉豆蔻酸使（KDO）(2)-（月桂酰）-脂质IV-A发生酰化反应。关于msbB基因敲除的报告描述了其对毒力的影响，但未提及在大肠杆菌K-12或沙门氏菌中存在生长缺陷的证据。我们的数据证实了msbB大肠杆菌K-12普遍不存在生长缺陷。相比之下，msbB鼠伤寒沙门氏菌血清型鼠伤寒杆菌对半乳糖-麦康凯培养基和6 mM EGTA培养基表现出明显的敏感性。在37摄氏度的Luria-Bertani（LB）肉汤中，msbB沙门氏菌细胞伸长、形成凸起且生长缓慢。msbB沙门氏菌在LB无盐（LB-0）琼脂上生长良好；然而，在LB-0肉汤的特定振荡条件下，许多msbB沙门氏菌细胞在指数生长期会裂解一部分细胞会形成丝状。msbB沙门氏菌在MSB（含有Mg(2+)和Ca(2+)的LB-0）肉汤（23至42摄氏度）中以接近野生型的生长速率生长。能部分抑制生长缺陷的基因外补偿性突变会高频自发出现，并且可以在选择生长更快衍生物的培养基上分离出突变体。其中一个抑制突变位于19.8厘摩处，是somA基因中的隐性IS10插入突变，somA是一个功能未知的基因，在大肠杆菌中对应于ybjX。此外，在未抑制的msbB菌株中进行的随机Tn10诱变产生了一组Tn10插入片段，这些片段不在msbB或somA中，而是与不同的抑制表型相关。因此，somA和其他基因中的插入突变可以抑制msbB表型。
