README.md from Symbiotic bacteria, immune-like sentinel cells, and the response to pathogens in a social amoeba

Some endosymbionts living within a host must modulate their hosts' immune systems in order to infect and persist. We studied the effect of a bacterial endosymbiont on a facultatively multicellular social amoeba host. Aggregates of the amoeba Dictyostelium discoideum contain a subpopulation of sentinel cells that function akin to the immune systems of more conventional multicellular organisms. Sentinel cells sequester and discard toxins from D. discoideum aggregates and may play a central role in defense against pathogens. We measured the number and functionality of sentinel cells in aggregates of D. discoideum infected by bacterial endosymbionts in the genus Paraburkholderia. Infected D. discoideum produced fewer and less functional sentinel cells, suggesting that Paraburkholderia may interfere with its host's immune system. Despite impaired sentinel cells, however, infected D. discoideum were less sensitive to ethidium bromide toxicity, suggesting that Paraburkholderia may also have a protective effect on its host. By contrast, D. discoideum infected by Paraburkholderia did not show differences in their sensitivity to two non-symbiotic pathogens. Our results expand previous work on yet another aspect of the complicated relationship between D. discoideum and Paraburkholderia, which has considerable potential as a model for the study of symbiosis.寄居宿主体内的部分内共生体（endosymbionts）需调控宿主免疫系统，方可成功侵染并持续存活于宿主体内。本研究聚焦于一株细菌内共生体对兼性多细胞社会性变形虫宿主的影响。盘基网柄菌（Dictyostelium discoideum）的聚集体中存在一类哨兵细胞（sentinel cells）亚群，其功能类似常规多细胞生物的免疫系统。哨兵细胞可捕获并清除盘基网柄菌聚集体中的毒素，且可能在宿主抵御病原体过程中发挥核心作用。我们对感染副伯克霍尔德菌属（Paraburkholderia）细菌内共生体的盘基网柄菌聚集体中的哨兵细胞数量与功能活性进行了检测。受感染的盘基网柄菌产生的哨兵细胞数量更少、功能更弱，这表明副伯克霍尔德菌可能会干扰宿主的免疫系统。尽管哨兵细胞功能受损，但受感染的盘基网柄菌对溴化乙锭（ethidium bromide）毒性的敏感性却有所降低，这提示副伯克霍尔德菌或许也能为宿主提供保护作用。与之相反，感染副伯克霍尔德菌的盘基网柄菌对两种非共生病原体的敏感性并无显著差异。本研究结果拓展了此前关于盘基网柄菌与副伯克霍尔德菌之间复杂共生关系的研究维度，二者作为共生研究模型具备极高的应用潜力。