Yan Jing, Nadell Carey D, Bassler Bonnie L
Department of Molecular Biology, Princeton University, Princeton, NJ, USA.
Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ, USA.
ISME J. 2017 Jul;11(7):1569-1577. doi: 10.1038/ismej.2017.33. Epub 2017 Mar 24.
Bacteria can grow in a free-swimming state, as planktonic cells, or in surface-attached communities, termed biofilms. The planktonic and biofilm growth modes differ dramatically with respect to spatial constraints, nutrient access, population density and cell-cell interactions. Fitness trade-offs underlie how successfully bacteria compete in each of these environments. Accordingly, some bacteria have evolved to be specialists in biofilm formation, while others specialize in planktonic growth. There are species, however, that possess flexible strategies: they can transition between the molecular programs required for biofilm formation and for planktonic growth. Such flexible strategies often sacrifice competitive ability against specialists in a given habitat. There is little exploration of the ecological conditions favoring the evolution of the flexible biofilm production strategy for bacteria in competition with specialist biofilm producers or specialist non-producers. Here, we study the human pathogen Vibrio cholerae, a flexible biofilm-former, as well as constitutive biofilm-producing and non-producing mutants. We assess the fitness of these strains under biofilm conditions, planktonic conditions and conditions that demand the ability to transition between the two growth modes. We show that, relative to the specialists, the wild type is superior at dispersal from biofilms to the planktonic phase; however, this capability comes at the expense of reduced competitive fitness against constitutive biofilm producers on surfaces. Wild-type V. cholerae can outcompete the constitutive biofilm producers and non-producers if habitat turnover is sufficiently frequent. Thus, selection for phenotypic flexibility in biofilm production depends on the frequency of environmental fluctuations encountered by bacteria.
细菌可以以自由游动的浮游细胞状态生长，也可以在附着于表面的群落（即生物膜）中生长。浮游生长模式和生物膜生长模式在空间限制、营养获取、种群密度以及细胞间相互作用方面存在显著差异。适应性权衡是细菌在这些环境中成功竞争的基础。因此，一些细菌进化成为生物膜形成的专家，而另一些则专门进行浮游生长。然而，有些物种具有灵活的策略：它们可以在生物膜形成和浮游生长所需的分子程序之间转换。这种灵活的策略往往会牺牲在特定栖息地与专家型菌株竞争的能力。目前很少有研究探讨有利于细菌灵活生物膜产生策略进化的生态条件，这种策略是在与专家型生物膜生产者或非生产者竞争时产生的。在这里，我们研究了人类病原体霍乱弧菌，一种具有灵活生物膜形成能力的细菌，以及组成型生物膜产生和不产生的突变体。我们评估了这些菌株在生物膜条件、浮游条件以及需要在两种生长模式之间转换的条件下的适应性。我们发现，相对于专家型菌株，野生型在从生物膜扩散到浮游阶段方面更具优势；然而，这种能力是以降低在表面与组成型生物膜生产者竞争的适应性为代价的。如果栖息地更替足够频繁，野生型霍乱弧菌可以胜过组成型生物膜生产者和非生产者。因此，对生物膜产生表型灵活性的选择取决于细菌遇到的环境波动频率。
