l-Arabinose Induces the Formation of Viable Nonproliferating Spheroplasts in Vibrio cholerae

ABSTRACT

Vibrio cholerae, the agent of the deadly human disease cholera, propagates as a curved rod-shaped bacterium in warm waters. It is sensitive to cold but persists in cold waters in the form of viable but nondividing coccoidal-shaped cells. Additionally, V. cholerae is able to form nonproliferating spherical cells in response to cell wall damage. It was recently reported that l-arabinose, a component of the hemicellulose and pectin of terrestrial plants, stops the growth of V. cholerae. Here, we show that l-arabinose induces the formation of spheroplasts that lose the ability to divide and stop growing in volume over time. However, they remain viable, and upon removal of l-arabinose, they start expanding in volume, form branched structures, and give rise to cells with a normal morphology after a few divisions. We further show that WigKR, a histidine kinase/response regulator pair implicated in the induction of high-level expression of cell wall synthetic genes, prevents the lysis of the spheroplasts during growth restart. Finally, we show that the physiological perturbations result from the import and catabolic processing of l-arabinose by the V. cholerae homolog of the Escherichia coli galactose transport and catabolic system. Taken together, our results suggest that the formation of nongrowing spherical cells is a common response of vibrios exposed to detrimental conditions. They also permit us to define conditions preventing any physiological perturbation of V. cholerae when using l-arabinose to induce gene expression from the tightly regulated promoter of the Escherichia coli araBAD operon.

IMPORTANCE Vibrio spp., among other bacteria, form transient cell wall-deficient forms as a response to different stresses and revert to proliferating rods when permissive conditions have been restored. Such cellular forms have been associated with antimicrobial tolerance, chronic infections, and environmental dispersion. The effect of l-Ara on V. cholerae could provide an easily tractable model to study the ability of vibrios to form viable reversible spheroplasts. Indeed, the quick transition to spheroplasts and reversion to proliferating rods by addition or removal of l-Ara are ideal to understand the genetic program governing this physiological state and the spatial rearrangements of the cellular machineries during cell shape transitions.