The Association of Cell Division Regulated by DicC With the Formation of Viable but Non-culturable Escherichia coli O157:H7.

Hanxu Pan,Kai Dong,Liang Zhao,Xiaojun Liao,Lei Rao,Yongtao Wang

doi:10.3389/fmicb.2019.02850

Abstract

The viable but non-culturable (VBNC) state, in which bacteria fail to grow on routine culture media but are actually alive, has been widely recognized as a strategy adopted by bacteria to cope with stressful environments. However, little is known regarding the molecular mechanism of VBNC formation. Here, we aimed to elucidate the specific roles of cell division regulatory proteins and the cell growth rate during VBNC Escherichia coli O157:H7 formation. We have previously found that expression of dicC is reduced by 20.08-fold in VBNC E. coli O157:H7 compared to non-VBNC cells. Little is known about DicC except that it, along with DicA, appears to act as a regulator of cell division by regulating expression of the cell division inhibitor DicB. First, our results showed that the VBNC cell number increased in the ΔdicC mutant as well as the DicA-overexpressing strain but decreased in the DicC-overexpressing strain induced by high-pressure carbon dioxide, acid, and H2O2. Furthermore, the growth rates of both the DicA-overexpressing strain and the ΔdicC mutant were higher than that of the control strain, while DicC-overexpressing strain grew significantly more slowly than the vector strain. The level of the dicB gene, regulated by dicA and dicC and inhibiting cell division, was increased in the DicC-overexpressing strain and decreased in the ΔdicC mutant and DicA-overexpressing strain, which was consistent with the growth phenotypes. In addition, the dwarfing cell morphology of the ΔdicC mutant and DicA-overexpressing strain were observed by SEM and TEM. Taken together, our study demonstrates that DicC negatively regulates the formation of the VBNC state, and DicA enhances the ability of cells to enter the VBNC state. Besides, the cell growth rate and dwarfing cell morphology may be correlated with the formation of the VBNC state.

Highlights

The viable but non-culturable (VBNC) state, a unique biological state, is a positive response strategy used by a number of bacteria to cope with different adverse environments (Colwell, 2000; Oliver, 2005b; Orruno et al, 2017). Xu et al (1982) found that Escherichia coli and Vibrio cholerae from seawater could not be cultured on their routine medium but possessed metabolic activity.Association Among DicC, Cell Division, and VBNCBased on this finding, they proposed the concept of the VBNC state, in which bacteria cannot grow on the routine culture medium but are alive
Transcriptomic data from a previous study showed that the expression of the dicC gene was downregulated by 20.08-fold in VBNC E. coli O157:H7 cells induced by high-pressure carbon dioxide (HPCD) (Zhao et al, 2016)
Similar to the above findings, the number of VBNC cells in the DicA strain was higher than that in the control strain (Figure 2C), indicating the role of DicC and DicA in the formation of the VBNC state. These results demonstrated that DicC negatively regulates the formation of VBNC E. coli O157:H7 induced by HPCD, while DicA could promote the process of VBNC cell formation

Summary

Introduction

The viable but non-culturable (VBNC) state, a unique biological state, is a positive response strategy used by a number of bacteria to cope with different adverse environments (Colwell, 2000; Oliver, 2005b; Orruno et al, 2017). Association Among DicC, Cell Division, and VBNC Based on this finding, they proposed the concept of the VBNC state, in which bacteria cannot grow on the routine culture medium but are alive. They proposed the concept of the VBNC state, in which bacteria cannot grow on the routine culture medium but are alive They further proved that these bacteria can recover from the VBNC state and become culturable again when the environment is suitable, which is termed resuscitation (Roszak et al, 1984). VBNC microorganisms are widely distributed in nature, representing a strategy used by microorganisms to survive in different adverse environments

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