Institute of Evolutionary Biology and Environmental Studies, University of Zurich, Switzerland.
J R Soc Interface. 2011 Dec 7;8(65):1772-84. doi: 10.1098/rsif.2011.0102. Epub 2011 May 18.
Filamentous bacteria are the oldest and simplest known multicellular life forms. By using computer simulations and experiments that address cell division in a filamentous context, we investigate some of the ecological factors that can lead to the emergence of a multicellular life cycle in filamentous life forms. The model predicts that if cell division and death rates are dependent on the density of cells in a population, a predictable cycle between short and long filament lengths is produced. During exponential growth, there will be a predominance of multicellular filaments, while at carrying capacity, the population converges to a predominance of short filaments and single cells. Model predictions are experimentally tested and confirmed in cultures of heterotrophic and phototrophic bacterial species. Furthermore, by developing a formulation of generation time in bacterial populations, it is shown that changes in generation time can alter length distributions. The theory predicts that given the same population growth curve and fitness, species with longer generation times have longer filaments during comparable population growth phases. Characterization of the environmental dependence of morphological properties such as length, and the number of cells per filament, helps in understanding the pre-existing conditions for the evolution of developmental cycles in simple multicellular organisms. Moreover, the theoretical prediction that strains with the same fitness can exhibit different lengths at comparable growth phases has important implications. It demonstrates that differences in fitness attributed to morphology are not the sole explanation for the evolution of life cycles dominated by multicellularity.
丝状细菌是已知最古老和最简单的多细胞生命形式。通过使用计算机模拟和实验来解决丝状环境中的细胞分裂问题，我们研究了一些生态因素，这些因素可能导致丝状生命形式出现多细胞生命周期。该模型预测，如果细胞分裂和死亡率取决于种群中细胞的密度，则会产生短丝和长丝之间可预测的循环。在指数增长期间，将存在大量的多细胞丝，而在承载能力下，种群趋于以短丝和单细胞为主。通过对异养和光合细菌物种的培养进行实验测试和验证了模型预测。此外，通过制定细菌种群的世代时间公式，可以表明世代时间的变化可以改变长度分布。该理论预测，给定相同的种群增长曲线和适应性，在可比的种群增长阶段，世代时间较长的物种的丝更长。对长度和每丝细胞数量等形态特性的环境依赖性进行特征描述，有助于理解简单多细胞生物中发育周期进化的先前条件。此外，理论预测表明，在可比的生长阶段具有相同适应性的菌株可以表现出不同的长度，这具有重要意义。它表明，归因于形态的适应性差异并不是以多细胞性为主的生命周期进化的唯一解释。
