Biology Department, Washington University in St. Louis, St. Louis, MO, USA.
ISME J. 2023 Dec;17(12):2352-2361. doi: 10.1038/s41396-023-01535-5. Epub 2023 Oct 26.
The soil amoeba Dictyostelium discoideum acts as both a predator and potential host for diverse bacteria. We tested fifteen Pseudomonas strains that were isolated from transiently infected wild D. discoideum for ability to escape predation and infect D. discoideum fruiting bodies. Three predation-resistant strains frequently caused extracellular infections of fruiting bodies but were not found within spores. Furthermore, infection by one of these species induces secondary infections and suppresses predation of otherwise edible bacteria. Another strain can persist inside of amoebae after being phagocytosed but is rarely taken up. We sequenced isolate genomes and discovered that predation-resistant isolates are not monophyletic. Many Pseudomonas isolates encode secretion systems and toxins known to improve resistance to phagocytosis in other species, as well as diverse secondary metabolite biosynthetic gene clusters that may contribute to predation resistance. However, the distribution of these genes alone cannot explain why some strains are edible and others are not. Each lineage may employ a unique mechanism for resistance.
土壤变形虫 Dictyostelium discoideum 既是捕食者，也是多种细菌的潜在宿主。我们测试了从短暂感染的野生 D. discoideum 中分离出的 15 株假单胞菌菌株，以测试它们逃避捕食和感染 D. discoideum 子实体的能力。三种抗捕食菌株经常导致子实体的细胞外感染，但在孢子中未发现。此外，其中一种物种的感染会引发二次感染，并抑制对其他可食用细菌的捕食。另一种菌株在被吞噬后可以在变形虫内持续存在，但很少被吸收。我们对分离株的基因组进行了测序，发现抗捕食分离株不是单系的。许多假单胞菌分离株编码分泌系统和毒素，已知这些系统和毒素可以提高其他物种对吞噬作用的抵抗力，以及多样化的次级代谢生物合成基因簇，这些基因簇可能有助于抗捕食作用。然而，这些基因的分布本身并不能解释为什么有些菌株是可食用的，而有些则不是。每个谱系可能都采用了独特的抵抗机制。
