细菌依靠细胞壁来防止物理和化学损害及渗透溶解，但研究人员却在一些细菌中发现了被认为没有细胞壁的罕见的L-型细胞。它们可能在躲避宿主免疫系统及青霉素等抗生素（它们以细胞壁合成为作用目标）的识别中发挥一定作用。
然而，L-型细胞非常难生长和操纵，因而难以研究。这种情况现在有可能改变，因为研究人员找到了培养常见模型生物B. subtilis 168的可通过基因手段跟踪的L-型细胞的一个途径。关于这一新系统的早期发现证实，L-型细胞的复制并不需要细胞壁合成，也不需要正常细胞分裂机制。相反，L-型细胞利用一个“extrusion-resolution”机制来增殖，通过一个步骤生成多种后代。这些发现在演化方面可能具有一定意义。细胞壁普遍见于各种细菌，所以很可能存在于这些古生物的最后共同祖先内。L-型细胞所采用的这一新颖的复制过程，有可能为了解细胞壁出现之前的增殖模式提供一个窗口。（生物谷Bioon.com）
生物谷推荐原始出处：
Nature 457, 849-853 (12 February 2009) | doi:10.1038/nature07742
Life without a wall or division machine in Bacillus subtilis
M. Leaver1, P. Domínguez-Cuevas1, J. M. Coxhead2, R. A. Daniel1 & J. Errington1
1 Institute for Cell and Molecular Biosciences, Newcastle University, Framlington Place, Newcastle Upon Tyne NE2 4HH, UK
2 Institute for Human Genetics, Newcastle University, International Centre for Life, Central Parkway, Newcastle Upon Tyne NE1 3BZ, UK
The cell wall is an essential structure for virtually all bacteria, forming a tough outer shell that protects the cell from damage and osmotic lysis. It is the target of our best antibiotics. L-form strains are wall-deficient derivatives of common bacteria that have been studied for decades. However, they are difficult to generate and typically require growth for many generations on osmotically protective media with antibiotics or enzymes that kill walled forms. Despite their potential importance for understanding antibiotic resistance and pathogenesis, little is known about their basic cell biology or their means of propagation. We have developed a controllable system for generating L-forms in the highly tractable model bacterium Bacillus subtilis. Here, using genome sequencing, we identify a single point mutation that predisposes cells to grow without a wall. We show that propagation of L-forms does not require the normal FtsZ-dependent division machine but occurs by a remarkable extrusion-resolution mechanism. This novel form of propagation provides insights into how early forms of cellular life may have proliferated.
