ComGA-RelA interaction and persistence in the Bacillus subtilis K-state.

Jeanette Hahn,Ileana M. Cristea,Andrew W. Tanner,Valerie J. Carabetta,David Dubnau

doi:10.1111/mmi.13040

Jeanette Hahn, Ileana M. Cristea + Show 3 more

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https://doi.org/10.1111/mmi.13040

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Abstract

The bistably expressed K-state of Bacillus subtilis is characterized by two distinct features; transformability and arrested growth when K-state cells are exposed to fresh medium. The arrest is manifested by a failure to assemble replisomes and by decreased rates of cell growth and rRNA synthesis. These phenotypes are all partially explained by the presence of the AAA(+) protein ComGA, which is also required for the binding of transforming DNA to the cell surface and for the assembly of the transformation pilus that mediates DNA transport. We have discovered that ComGA interacts with RelA and that the ComGA-dependent inhibition of rRNA synthesis is largely bypassed in strains that cannot synthesize the alarmone (p)ppGpp. We propose that the interaction of ComGA with RelA prevents the hydrolysis of (p)ppGpp in K-state cells, which are thus trapped in a non-growing state until ComGA is degraded. We show that some K-state cells exhibit tolerance to antibiotics, a form of type 1 persistence, and we propose that the bistable expression of both transformability and the growth arrest are bet-hedging adaptations that improve fitness in the face of varying environments, such as those presumably encountered by B. subtilis in the soil.

Highlights

The state of competence for transformation in Bacillus subtilis is activated by the transcription factor ComK and exhibits two distinct features compared with most other characterized transformable bacteria; it is bistably expressed in a minority of the cells in a clonal population and the expressing cells are growth-arrested
The division times of both KS and non-KS cells in several experiments were broadly distributed, the non-KS cells typically divided after 45–60 minutes, while the majority of KS cells divided between 110–180 minutes after exposure to fresh growth medium
Since ComGA associates with RelA we considered whether the ComGA-associated phenotypes may be due to an increase in the intracellular pool of (p)ppGpp, as suggested by the synthetic slow growth phenotype of E. coli co-expressing ComGA and the B. subtilis RelA

Summary

Introduction

The state of competence for transformation in Bacillus subtilis is activated by the transcription factor ComK and exhibits two distinct features compared with most other characterized transformable bacteria; it is bistably expressed in a minority of the cells in a clonal population and the expressing cells are growth-arrested. Two ComK-induced proteins, ComGA and Maf (Butler et al, 1993), are known to be involved in the inhibition of cell division in KS cells (Briley et al, 2011b, Haijema et al, 2001). ComGA is a membrane associated AAA+ (ATPases associated with diverse cellular activities) protein, which inhibits cell division and plays a role in the binding of transforming DNA to the cell and is required for the construction of the competence-associated pseudopilus needed for DNA transport (Briley et al, 2011a). The role, if any, of this pyrophosphatase activity in the ability of Maf to inhibit cell division is not clear

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