Department of Chemical Engineering, University of Pennsylvania, 19104, Philadelphia, Pennsylvania, USA.
Microb Ecol. 1988 Sep;16(2):115-31. doi: 10.1007/BF02018908.
Although the dynamic behavior of microbial populations in nonmixed systems is a central aspect of many problems in biochemical engineering and microbiology, the factors that govern this behavior are not well understood. In particular, the effects of bacterial chemotaxis (biased migration of cells in the direction of chemical concentration gradients) have been the subject of much speculation but very little quantitative investigation. In this paper, we provide the first theoretical analysis of the effects of bacterial chemotaxis on the dynamics of competition between two microbial populations for a single rate-limiting nutrient in a confined nonmixed system. We use a simple unstructured model for cell growth and death, and the most soundly based current model for cell population migration. Using numerical finite element techniques, we examine both transient and steady-state behavior of the competing populations, focusing primarily on the influence of the cell random motility coefficient,μ, and the cell chemotaxis coefficient, χ. We find that, in general, there are four possible steady-state outcomes: both populations die out, population 1 exists alone, population 2 exists alone, and the two populations coexist. We find that, in contrast to well-mixed systems, the slower-growing population can coexist and even exist alone if it possesses sufficiently superior motility and chemotaxis properties. Our results allow estimation of the value of χ necessary to allow coexistence and predominance for reasonable values of growth and random motility parameters in common systems. An especially intriguing finding is that there is a minimum value of χ necessary for a chemotactic population to have a competitive advantage over an immotile population in a confined nonmixed system. Further, for typical system parameter values, this minimum value of χ is the range of values that can be estimated from independent experimental assays for chemotaxis.Thus, in typical nonmixed systems, cell motility and chemotaxis properties can be the determining factors in governing population dynamics.
尽管非混合系统中微生物种群的动态行为是生化工程和微生物学许多问题的核心方面，但控制这种行为的因素还没有得到很好的理解。特别是，细菌趋化性（细胞在化学浓度梯度方向上的偏转移）的影响一直是很多推测的主题，但很少有定量研究。在本文中，我们首次对细菌趋化性对两种微生物种群在受限非混合系统中单一限速营养物质竞争动力学的影响进行了理论分析。我们使用简单的无结构细胞生长和死亡模型，以及目前基于最合理的细胞群体迁移模型。使用数值有限元技术，我们研究了竞争群体的瞬态和稳态行为，主要关注细胞随机迁移系数μ和细胞趋化系数χ的影响。我们发现，一般来说，有四种可能的稳态结果：两种群体都灭绝，种群 1 单独存在，种群 2 单独存在，两种群体共存。我们发现，与混合良好的系统相比，如果较慢生长的种群具有足够优越的运动性和趋化性特性，则可以共存甚至单独存在。我们的结果允许估计在常见系统中合理的生长和随机迁移参数值下，允许共存和占优势所需的χ值。一个特别有趣的发现是，在受限非混合系统中，趋化性种群相对于无运动性种群具有竞争优势所需的χ值存在最小值。此外，对于典型的系统参数值，这个最小的χ值是可以从独立的趋化性实验测定中估计的值的范围。因此，在典型的非混合系统中，细胞运动性和趋化性特性可以成为控制种群动态的决定因素。
