Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, Ontario, Canada.
Institute for Infectious Disease Research, McMaster University, Hamilton, Ontario, Canada.
mBio. 2024 Apr 10;15(4):e0242423. doi: 10.1128/mbio.02424-23. Epub 2024 Mar 12.
Two growth modes have been described for the filamentous bacteria. Their classic developmental life cycle culminates in the formation of dormant spores, where movement to new environments is mediated through spore dispersal. In contrast, exploratory growth proceeds as a rapidly expanding vegetative mycelium that leads to extensive surface colonization and is associated with the release of volatile compounds that promote alkalinization (and reduced iron bioavailability) of its surrounding environment. Here, we report that exploratory growth in can proceed in tandem with classic sporulating development in response to specific nutritional cues. Sporulating exploration is not accompanied by a rise in environmental pH but has the same iron acquisition requirements as conventional exploration. We found that mutants that were defective in their ability to sporulate were unaffected in exploration, but mutants undergoing precocious sporulation were compromised in their exploratory growth and this appeared to be mediated through premature activation of the developmental regulator WhiI. Cell envelope integrity was also found to be critical for exploration, as mutations in the cell envelope stress-responsive extracytoplasmic function sigma factor SigE led to a failure to explore robustly under all exploration-promoting conditions. Finally, in expanding the known exploration-promoting conditions, we discovered that the model species exhibited exploration capabilities, supporting the proposal that exploration is conserved across diverse streptomycetes.
bacteria have evolved diverse developmental and metabolic strategies to thrive in dynamic environmental niches. Here, we report the amalgamation of previously disparate developmental pathways, showing that colony expansion via exploration can proceed in tandem with colony sporulation. This developmental integration extends beyond phenotype to include shared genetic elements, with sporulation-specific repressors being required for successful exploration. Comparing this new exploration mode with previously identified strategies has revealed key differences (e.g., no need for environmental alkalinization), and simultaneously allowed us to define unifying requirements for exploration. The "reproductive exploration" phenomenon reported here represents a unique bet-hedging strategy, with the colony engaging in an aggressive colonization strategy while transporting a protected genetic repository.
丝状细菌有两种生长模式。它们经典的发育生命周期以休眠孢子的形成而告终，而新环境的运动则通过孢子传播来介导。相比之下，探索性生长以快速扩展的营养菌丝体进行，导致广泛的表面定植，并与挥发性化合物的释放有关，这些化合物促进其周围环境的碱化（降低铁的生物利用度）。在这里，我们报告说，在特定营养线索的作用下，丝状可以与经典的孢子形成发育同时进行探索性生长。孢子形成的探索并没有伴随着环境 pH 值的升高，但它具有与传统探索相同的铁获取要求。我们发现，在孢子形成能力有缺陷的突变体中，探索不受影响，但过早进行孢子形成的突变体在探索性生长中受到损害，这似乎是通过发育调节剂 WhiI 的过早激活来介导的。细胞壁完整性也被发现对探索至关重要，因为细胞外功能 sigma 因子 SigE 的细胞壁应激反应突变体在所有促进探索的条件下都无法强有力地探索。最后，在扩大已知的探索促进条件下，我们发现模式种 也表现出探索能力，支持了探索在不同的链霉菌中保守的观点。
具有进化出多样的发育和代谢策略，以在动态环境小生境中茁壮成长。在这里，我们报告了以前不同发育途径的合并，表明通过探索进行菌落扩张可以与菌落孢子形成同时进行。这种发育整合不仅扩展到表型，还包括共享的遗传元件，成功探索需要孢子形成特异性的抑制剂。将这种新的探索模式与以前确定的策略进行比较，揭示了关键差异（例如，不需要环境碱化），同时也使我们能够定义 探索的统一要求。这里报道的“生殖探索”现象代表了一种独特的风险对冲策略， 菌落采用积极的定植策略，同时携带受保护的遗传库。
