Center for Nonlinear Dynamics and Department of Physics, University of Texas at Austin, Austin, Texas, USA.
mBio. 2011 May 31;2(3):e00069-11. doi: 10.1128/mBio.00069-11. Print 2011.
Natural habitats vary in available nutrients and room for bacteria to grow, but successful colonization can lead to overcrowding and stress. Here we show that competing sibling colonies of Paenibacillus dendritiformis bacteria survive overcrowding by switching between two distinct vegetative phenotypes, motile rods and immotile cocci. Growing colonies of the rod-shaped bacteria produce a toxic protein, Slf, which kills cells of encroaching sibling colonies. However, sublethal concentrations of Slf induce some of the rods to switch to Slf-resistant cocci, which have distinct metabolic and resistance profiles, including resistance to cell wall antibiotics. Unlike dormant spores of P. dendritiformis, the cocci replicate. If cocci encounter conditions that favor rods, they secrete a signaling molecule that induces a switch to rods. Thus, in contrast to persister cells, P. dendritiformis bacteria adapt to changing environmental conditions by inducible and reversible phenotypic switching.
In favorable environments, species may face space and nutrient limits due to overcrowding. Bacteria provide an excellent model for analyzing principles underlying overcrowding and regulation of density in nature, since their population dynamics can be easily and accurately assessed under controlled conditions. We describe a newly discovered mechanism for survival of a bacterial population during overcrowding. When competing with sibling colonies, Paenibacillus dendritiformis produces a lethal protein (Slf) that kills cells at the interface of encroaching colonies. Slf also induces a small proportion of the cells to switch from motile, rod-shaped cells to nonmotile, Slf-resistant, vegetative cocci. When crowding is reduced and nutrients are no longer limiting, the bacteria produce a signal that induces cocci to switch back to motile rods, allowing the population to spread. Genes encoding components of this phenotypic switching pathway are widespread among bacterial species, suggesting that this survival mechanism is not unique to P. dendritiformis.
自然栖息地的营养物质和细菌生长的空间各不相同，但成功的定殖可能导致过度拥挤和压力。在这里，我们表明，分枝杆菌的竞争姐妹菌落通过在两种不同的营养体表型之间切换来在过度拥挤的情况下存活下来，这两种表型是运动的杆状和不运动的球菌。生长中的杆状细菌菌落产生一种有毒的蛋白质 Slf，它杀死入侵的姐妹菌落的细胞。然而，Slf 的亚致死浓度诱导一些杆状细胞转换为 Slf 抗性球菌，后者具有不同的代谢和抗性特征，包括对细胞壁抗生素的抗性。与分枝杆菌的休眠孢子不同，球菌会繁殖。如果球菌遇到有利于杆状细胞的条件，它们会分泌一种信号分子，诱导它们向杆状细胞转变。因此，与持久细胞不同，分枝杆菌通过可诱导和可逆的表型转换来适应不断变化的环境条件。
在有利的环境中，由于过度拥挤，物种可能会面临空间和营养限制。细菌为分析自然中过度拥挤和密度调节的原理提供了一个极好的模型，因为它们的种群动态可以在受控条件下轻松准确地评估。我们描述了一种新发现的细菌种群在过度拥挤时生存的机制。当与姐妹菌落竞争时，分枝杆菌会产生一种致命的蛋白质（Slf），该蛋白质会杀死侵入菌落界面的细胞。Slf 还诱导一小部分细胞从运动的杆状细胞转换为非运动的、Slf 抗性的营养球菌。当拥挤减少且营养不再受到限制时，细菌会产生一种信号，诱导球菌回到运动的杆状细胞，从而使种群扩散。编码这种表型转换途径的基因在细菌物种中广泛存在，这表明这种生存机制并非分枝杆菌所特有。
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