Sentinel cells, symbiotic bacteria, and toxin resistance in the social amoeba Dictyostelium discoideum

The social amoeba Dictyostelium discoideum is unusual among eukaryotes in having both unicellular and multicellular stages. In the multicellular stage, some cells, called sentinels, ingest toxins, waste, and bacteria. The sentinel cells ultimately fall away from the back of the migrating slug, thus removing these substances from the slug. However, some D. discoideum clones called farmers carry commensal bacteria through the multicellular stage while others called non-farmers do not. Farmers profit from their beneficial bacteria. To prevent the loss of these bacteria, we hypothesize that sentinel cell numbers may be reduced in farmers and thus farmers may have a diminished capacity to respond to pathogenic bacteria or toxins. In support, we found that farmers have fewer sentinel cells compared to non-farmers. However, farmers produced no fewer viable spores when challenged with a toxin. These results are consistent with the beneficial bacteria, Burkholderia, providing protection ...盘基网柄菌（Dictyostelium discoideum）是一类特殊的真核生物，兼具单细胞与多细胞生命周期阶段。在多细胞阶段，部分被命名为哨兵细胞（sentinel）的细胞会吞噬毒素、代谢废物与细菌。此类哨兵细胞最终会从迁移中的蛞蝓体（slug）后端脱落，进而将上述物质从蛞蝓体中清除。不过，部分盘基网柄菌克隆被称为农场型克隆（farmers），可在多细胞阶段携带共生细菌（commensal bacteria），而另一类非农场型克隆（non-farmers）则不具备该能力。农场型克隆可从其共生有益菌中获取收益。为防止此类有益菌流失，我们提出假说：农场型克隆的哨兵细胞数量可能有所降低，因此其应对病原菌（pathogenic bacteria）或毒素的能力会减弱。为验证该假说，我们发现农场型克隆的哨兵细胞数量确实少于非农场型克隆。但在经毒素胁迫处理后，农场型克隆产生的存活孢子（viable spores）数量并未减少。上述结果与伯克霍尔德氏菌（Burkholderia）这类有益菌提供保护的推论相符……