Department of Plant Pathology and Microbiology, Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel.
Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel.
mBio. 2024 Aug 14;15(8):e0071524. doi: 10.1128/mbio.00715-24. Epub 2024 Jul 22.
The bacterial predator is considered to be obligatorily prey (host)-dependent (H-D), and thus unable to form biofilms. However, spontaneous host-independent (H-I) variants grow axenically and can form robust biofilms. A screen of 350 H-I mutants revealed that single mutations in stator genes or were sufficient to generate flagellar motility-defective H-I strains able to adhere to surfaces but unable to develop biofilms. The variants showed large transcriptional shifts in genes related to flagella, prey-invasion, and cyclic-di-GMP (CdG), as well as large changes in CdG cellular concentration relative to the H-D parent. The introduction of the parental allele resulted in a full reversion to the H-D phenotype, but we propose that specific interactions between stator proteins prevented functional complementation by paralogs. In contrast, specific mutations in a pilus-associated protein (Bd0108) mutant background were necessary for biofilm formation, including secretion of extracellular DNA (eDNA), proteins, and polysaccharides matrix components. Remarkably, disruption strongly reduced biofilm development. All H-I variants grew similarly without prey, showed a strain-specific reduction in predatory ability in prey suspensions, but maintained similar high efficiency in prey biofilms. Population-wide allele sequencing suggested additional routes to host independence. Thus, stator and invasion pole-dependent signaling control the H-D and the H-I biofilm-forming phenotypes, with single mutations overriding prey requirements, and enabling shifts from obligate to facultative predation, with potential consequences on community dynamics. Our findings on the facility and variety of changes leading to facultative predation also challenge the concept of and like organisms being obligate predators.
The ability of bacteria to form biofilms is a central research theme in biology, medicine, and the environment. We show that cultures of the obligate (host-dependent) "solitary" predatory bacterium , which cannot replicate without prey, can use various genetic routes to spontaneously yield host-independent (H-I) variants that grow axenically (as a single species, in the absence of prey) and exhibit various surface attachment phenotypes, including biofilm formation. These routes include single mutations in flagellar stator genes that affect biofilm formation, provoke motor instability and large motility defects, and disrupt cyclic-di-GMP intracellular signaling. H-I strains also exhibit reduced predatory efficiency in suspension but high efficiency in prey biofilms. These changes override the requirements for prey, enabling a shift from obligate to facultative predation, with potential consequences on community dynamics.
被认为是强制性猎物（宿主）依赖（H-D）的细菌捕食者，因此无法形成生物膜。然而，自发的宿主独立（H-I）变体可以在无宿主的情况下生长，并能形成强大的生物膜。对 350 个 H-I 突变体的筛选表明，定子基因 或 的单一突变足以产生鞭毛运动缺陷的 H-I 菌株，这些菌株能够附着在表面上，但无法形成生物膜。这些变体在与鞭毛、猎物入侵和环二鸟苷（CdG）相关的基因以及 CdG 细胞浓度相对于 H-D 亲本的大量变化方面表现出明显的转录变化。引入亲本 等位基因导致完全恢复到 H-D 表型，但我们提出定子蛋白的特定相互作用阻止了 旁系同源物的功能互补。相比之下，在菌毛相关蛋白（Bd0108）突变体背景下，特定突变对于生物膜形成是必要的，包括细胞外 DNA（eDNA）、蛋白质和多糖基质成分的分泌。值得注意的是， 缺失强烈降低了生物膜的形成。所有 H-I 变体在没有猎物的情况下生长相似，在猎物悬浮液中表现出特定的捕食能力降低，但在猎物生物膜中保持相似的高效率。全种群等位基因测序表明了其他获得宿主独立性的途径。因此，定子和入侵极依赖信号控制 H-D 和 H-I 生物膜形成表型，单个突变可克服猎物的要求，并使从专性捕食转变为兼性捕食成为可能，这可能对群落动态产生影响。我们关于导致兼性捕食的各种变化的便利性和多样性的发现也挑战了像 这样的生物体是专性捕食者的概念。
细菌形成生物膜的能力是生物学、医学和环境领域的一个核心研究主题。我们表明，专性（宿主依赖）“孤独”捕食菌 的培养物不能在没有猎物的情况下复制，它可以使用各种遗传途径自发产生宿主独立（H-I）变体，这些变体可以在无宿主的情况下（作为单一物种生长，没有猎物）生长，并表现出各种表面附着表型，包括生物膜形成。这些途径包括影响生物膜形成的鞭毛定子基因的单一突变，引发马达不稳定性和大的运动缺陷，并破坏环二鸟苷（c-di-GMP）细胞内信号。H-I 菌株在悬浮液中的捕食效率也降低，但在猎物生物膜中效率很高。这些变化克服了对猎物的要求，使从专性捕食到兼性捕食的转变成为可能，这可能对群落动态产生影响。
