We use mathematical modelling to examine how microbial strain communities are structured by the host specialisation traits and antigenic relationships of their members. The model is quite general and broadly applicable, but we focus on Borrelia burgdorferi, the Lyme disease bacterium, transmitted by ticks to mice and birds. In this system, host specialisation driven by the evasion of innate immunity has been linked to multiple niche polymorphism, while antigenic differentiation driven by the evasion of adaptive immunity has been linked to negative frequency dependence. Our model is composed of two host species, one vector, and multiple co-circulating pathogen strains that vary in their host specificity and their antigenic distances from one another. We explore the conditions required to maintain pathogen diversity. We show that the combination of host specificity and antigenic differentiation creates an intricate niche structure. Unequivocal rules that relate the stability of a strain community directly to the trait composition of its members are elusive. However, broad patterns are evident. When antigenic differentiation is weak, stable communities are typically composed entirely of generalists that can exploit either host species equally well. As antigenic differentiation increases, more diverse stable communities emerge, typically around trait compositions of generalists, generalists and very similar specialists, and specialists roughly balanced between the two host species.

我们使用数学模型来检查微生物菌株群落是如何由宿主专业化特征和其成员的抗原关系构成的。该模型非常普遍且适用广泛，但我们关注的是伯氏疏螺旋体，莱姆病细菌，由蜱传播给老鼠和鸟类。在这个系统中，逃避先天免疫驱动的宿主特化与多重生态位多态性有关，而逃避适应性免疫驱动的抗原分化与负频率依赖性有关。我们的模型由两种宿主物种、一种载体和多种共同循环的病原体菌株组成，这些菌株的宿主特异性和彼此之间的抗原距离各不相同。我们探索维持病原体多样性所需的条件。我们表明，宿主特异性和抗原分化的结合创造了一个复杂的生态位结构。将菌株群落的稳定性直接与其成员的性状组成联系起来的明确规则是难以捉摸的。然而，广泛的模式是显而易见的。当抗原分化较弱时，稳定的群落通常完全由可以同样利用任一宿主物种的通才组成。随着抗原分化的增加，出现了更多样化的稳定群落，通常围绕通才、通才和非常相似的专家的性状组成，以及在两个宿主物种之间大致平衡的专家。