EtBr data for log2Fold change graph.xlsx 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 <i>Dictyostelium discoideum</i> 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 <i>D. discoideum</i> aggregates and may play a central role in defense against pathogens. We measured the number and functionality of sentinel cells in aggregates of <i>D. discoideum</i> infected by bacterial endosymbionts in the genus <i>Paraburkholderia</i>. Infected <i>D. discoideum</i> produced fewer and less functional sentinel cells, suggesting that <i>Paraburkholderia</i> may interfere with its host's immune system. Despite impaired sentinel cells, however, infected <i>D. discoideum</i> were less sensitive to ethidium bromide toxicity, suggesting that <i>Paraburkholderia</i> may also have a protective effect on its host. By contrast, <i>D. discoideum</i> infected by <i>Paraburkholderia</i> 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 <i>D. discoideum</i> and <i>Paraburkholderia</i>, which has considerable potential as a model for the study of symbiosis.

部分生活于宿主体内的内共生菌（endosymbionts）为实现感染与持续定殖，必须调控宿主的免疫系统。本研究探讨了一株细菌内共生菌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，其功能类似高等多细胞生物的免疫系统。哨兵细胞可截留并清除盘基网柄菌聚集体中的毒素，在宿主抵御病原体的过程中发挥核心作用。本研究对被帕拉伯克霍尔德菌属（Paraburkholderia）细菌内共生菌感染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，这表明帕拉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，提示帕拉伯克霍尔德菌或许还能为宿主提供保护作用。与之相反，被帕拉伯克霍尔德菌感染的盘基网柄菌，对两种非共生病原体的敏感性并未出现显著差异。本研究结果拓展了此前关于盘基网柄菌与帕拉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有极高的应用潜力。