Department of Plant Sciences, University of Oxford, Oxford, United Kingdom.
PLoS One. 2007 Aug 15;2(8):e740. doi: 10.1371/journal.pone.0000740.
Bacterial adaptation to new environments often leads to the establishment of new genotypes with significantly altered phenotypes. In the Wrinkly Spreader (WS), ecological success in static liquid microcosms was through the rapid colonisation of the air-liquid interface by the production of a cellulose-based biofilm. Rapid surface spreading was also seen on agar plates, but in this two-dimensional environment the WS appears maladapted and rapidly reverts to the ancestral smooth (SM)-like colony genotype. In this work, the fitness of WS relative to SM in mixed colonies was found to be low, confirming the WS instability on agar plates. By examining defined WS mutants, the maladaptive characteristic was found to be the expression of cellulose. SM-like revertants had a higher growth rate than WS and no longer expressed significant amounts of cellulose, further confirming that the expression of this high-cost polymer was the basis of maladaptation and the target of compensatory mutation in developing colonies. However, examination of the fate of WS-founded populations in either multiple-colony or single mega-colony agar plate microcosms demonstrated that the loss of WS lineages could be reduced under conditions in which the rapid spreading colony phenotype could dominate nutrient and oxygen access more effectively than competing SM/SM-like genotypes. WS-like isolates recovered from such populations showed increased WS phenotype stability as well as changes in the degree of colony spreading, confirming that the WS was adapting to the two-dimensional agar plate microcosm.
细菌对新环境的适应常常导致新基因型的建立，这些基因型的表型有明显改变。在褶皱扩展菌（WS）中，在静态液体微环境中的生态成功是通过产生基于纤维素的生物膜来快速定殖气液界面。在琼脂平板上也观察到快速表面扩散，但在这种二维环境中，WS 似乎适应不良，并迅速恢复到祖先的光滑（SM）样菌落基因型。在这项工作中，发现 WS 相对于 SM 在混合菌落中的适应性较低，这证实了 WS 在琼脂平板上的不稳定性。通过检查定义明确的 WS 突变体，发现适应性差的特征是纤维素的表达。SM 样回复变体的生长速度高于 WS，并且不再表达大量纤维素，这进一步证实了这种高成本聚合物的表达是适应不良的基础，也是在发育中的菌落中发生补偿性突变的目标。然而，对多菌落或单一大菌落琼脂平板微宇宙中 WS 种群的命运进行检查表明，在快速扩散的菌落表型能够比竞争的 SM/SM 样基因型更有效地获取营养和氧气的情况下，可以减少 WS 谱系的丧失。从这些种群中回收的 WS 样分离株显示出 WS 表型稳定性的增加以及菌落扩散程度的变化，这证实了 WS 正在适应二维琼脂平板微宇宙。
