Department of Molecular and Cellular Biology, Harvard University, Cambridge, Massachusetts, USA.
Department of Molecular and Cellular Biology, Harvard University, Cambridge, Massachusetts, USA
J Bacteriol. 2019 Oct 21;201(22). doi: 10.1128/JB.00420-19. Print 2019 Nov 15.
Lipopolysaccharide (LPS) is normally considered to be essential for viability in Gram-negative bacteria but can be removed in Mutant cells lacking this component of the outer membrane show growth and morphological defects. Here, we report that growth rates equivalent to the wild type can be achieved simply by propagation in minimal medium. The loss of LPS requires that cells rely on phospholipids for both leaflets of the outer membrane. We show that growth rate in the absence of LPS is not limited by nutrient availability but by the rate of outer membrane biogenesis. We hypothesize that because cells grow more slowly, outer membrane synthesis ceases to be rate limiting in minimal medium. Gram-negative bacteria are defined by their asymmetric outer membrane that consists of phospholipids on the inner leaflet and lipopolysaccharide (LPS) in the outer leaflet. LPS is essential in all but a few Gram-negative species; the reason for this differential essentiality is not well understood. One species that can survive without LPS, , shows characteristic growth and morphology phenotypes. We show that these phenotypes can be suppressed under conditions of slow growth and describe how LPS loss is connected to the growth defects. In addition to better defining the challenges cells face in the absence of LPS, we provide a new hypothesis that may explain the species-dependent conditional essentiality.
脂多糖 (LPS) 通常被认为是革兰氏阴性菌生存所必需的，但在外膜缺少这种成分的突变细胞中可以去除。缺失这种成分的突变细胞表现出生长和形态缺陷。在这里，我们报告说，仅仅通过在最小培养基中繁殖，就可以达到与野生型相当的生长速度。 LPS 的缺失要求细胞依赖磷脂来形成外膜的两个叶。我们表明，在没有 LPS 的情况下，生长速率不受营养物质可用性的限制，而是受外膜生物发生的速率限制。我们假设，由于细胞生长较慢，在外膜合成不再是最小培养基中限速步骤。革兰氏阴性菌的定义是其不对称的外膜，由内层的磷脂和外层的脂多糖 (LPS) 组成。 LPS 在除少数革兰氏阴性菌以外的所有物种中都是必需的；这种差异性必需性的原因尚不清楚。有一种可以在没有 LPS 的情况下存活的物种 ， ，它表现出典型的生长和形态表型。我们表明，这些表型可以在缓慢生长的条件下被抑制，并描述了 LPS 缺失如何与生长缺陷相关联。除了更好地定义细胞在没有 LPS 的情况下所面临的挑战外，我们还提出了一个新的假设，可能解释了物种依赖性条件必需性。
