Bistable expression of the Salmonella enterica pathogenicity island 1 (SPI-1) and the flagellar network (Flag) has been described previously. In this study, simultaneous monitoring of OFF and ON states in SPI-1 and in the flagellar regulon reveals independent switching, with concomitant formation of four subpopulations: SPI-1^OFF Flag^OFF, SPI-1^OFF Flag^ON, SPI-1^ON Flag^OFF, and SPI-1^ON Flag^ON. Invasion assays upon cell sorting show that none of the four subpopulations is highly invasive, thus raising the possibility that Flag^OFF cells might contribute to optimal invasion as previously proposed for SPI-1^OFF cells. Time lapse microscopy observation indicates that expression of the flagellar regulon contributes to the growth impairment previously described in SPI-1^ON cells. As a consequence, growth resumption in SPI-1^ON Flag^ON cells requires switching to both SPI-1^OFF and Flag^OFF states.

中文翻译：

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肠道沙门氏菌中致病岛1和鞭毛调节基因双稳态表达的单细胞分析

先前已经描述了肠沙门氏菌致病岛1（SPI-1）和鞭毛网络（Flag）的双稳态表达。在这项研究中，同时监视SPI-1和鞭毛调节器中的OFF和ON状态揭示了独立​​的切换，并伴随着四个亚群的形成：SPI-1 ^OFF标志^OFF，SPI-1 ^OFF标志^ON，SPI-1 ^ON标志^OFF，并且SPI-1 ^ON标志为^ON。细胞分选后的侵袭分析表明，这四个亚群均没有高度侵袭性，因此增加了将标志^关闭的可能性如先前针对SPI-1 ^OFF细胞所提出的，细胞可能有助于最佳侵袭。延时显微镜观察表明，鞭毛调节子的表达有助于先前在SPI-1 ^ON细胞中描述的生长障碍。结果，在SPI-1 ^ON Flag ^ON单元中恢复生长需要同时切换到SPI-1 ^OFF和Flag ^OFF状态。