Angert E R, Losick R M
Department of Molecular and Cellular Biology, Harvard University, The Biological Laboratories, 16 Divinity Avenue, Cambridge, MA 02138, USA.
Proc Natl Acad Sci U S A. 1998 Aug 18;95(17):10218-23. doi: 10.1073/pnas.95.17.10218.
The Gram-positive bacterium Metabacterium polyspora is an uncultivated symbiont of the guinea pig gastrointestinal tract. Here we present evidence that in M. polyspora vegetative cell division has taken on a minor, and apparently dispensable, role in propagation. Instead, this unusual bacterium has evolved the capacity to produce progeny in the form of multiple endospores. Endospore formation is coordinated with transit of the bacterium through the gastrointestinal tract of the guinea pig. For the majority of cells, sporulation is initiated in the ileum, whereas later stages of development take place in the cecum. We show that multiple endospores are generated both by asymmetric division at both poles of the cell and by symmetric division of the endospores at an early stage of their development. Our findings suggest that M. polyspora represents an intermediate step in the evolution of a novel mode of cellular propagation that originates with endospore-forming Bacillus and Clostridium spp., which reproduce by binary fission, and extends to Epulopiscium spp., which create multiple viviparous offspring by a process of internal reproduction.
革兰氏阳性菌多孢变形菌是豚鼠胃肠道中一种未培养的共生菌。在此，我们提供证据表明，在多孢变形菌中，营养细胞分裂在繁殖过程中发挥的作用较小，而且显然并非必不可少。相反，这种不寻常的细菌已经进化出以多个内生孢子的形式产生后代的能力。内生孢子的形成与该细菌在豚鼠胃肠道中的迁移过程相协调。对于大多数细胞来说，孢子形成在回肠中开始，而发育的后期阶段则在盲肠中进行。我们发现，多个内生孢子既通过细胞两极的不对称分裂产生，也通过内生孢子在发育早期的对称分裂产生。我们的研究结果表明，多孢变形菌代表了一种新型细胞繁殖模式进化过程中的一个中间阶段，这种模式起源于通过二分裂进行繁殖的产内生孢子的芽孢杆菌属和梭菌属，并延伸至通过内部繁殖过程产生多个胎生后代的巨大芽孢杆菌属。
