Bacterial persisters are non-growing cells that are highly tolerant to bactericidal antibiotics. However, this tolerance is reversible and not mediated by heritable genetic changes. Lon, an ATP-dependent protease, has repeatedly been shown to play a critical role in fluoroquinolone persistence. Although lon deletion (Δlon) is thought to kill persister cells via accumulation of the cell division inhibitor protein SulA, the exact mechanism underlying this phenomenon has yet to be elucidated. Here, we show that Lon is an important regulatory protein for the resuscitation of the fluoroquinolone persisters in Escherichia coli, and lon deletion impairs the ability of persister cells to form colonies during recovery, without killing these cells, through a sulA- and ftsZ-dependent mechanism. Notably, this observed non-culturable state of antibiotic-tolerant Δlon cells is transient, as environmental conditions, such as starvation, can restore their culturability. Our data further indicate that starvation-induced SulA degradation or expression of Lon during recovery facilitates Z-ring formation in Δlon persisters. Calculating the ratio of the cell length (L in µm) to the number of Z-rings (Z) for each ofloxacin-treated intact cell analyzed has revealed a strong correlation between persister resuscitation and calculated L/Z values, which represents a potential biomarker for Δlon persisters that are transitioning to the normal cell state under the conditions studied here.

This is a companion discussion topic for the original entry at https://doi.org/10.1101/2021.09.22.461453