A Cell Cycle and Nutritional Checkpoint Controlling Bacterial Surface Adhesion

Abstract

In natural environments, bacteria often adhere to surfaces where they form complex multicellular communities. Surface adherence is determined by the biochemical composition of the cell envelope. We describe a novel regulatory mechanism by which the bacterium, Caulobacter crescentus, integrates cell cycle and nutritional signals to control development of an adhesive envelope structure known as the holdfast. Specifically, we have discovered a 68-residue protein inhibitor of holdfast development (HfiA) that directly targets a conserved glycolipid glycosyltransferase required for holdfast production (HfsJ). Multiple cell cycle regulators associate with the hfiA and hfsJ promoters and control their expression, temporally constraining holdfast development to the late stages of G1. HfiA further functions as part of a ‘nutritional override’ system that decouples holdfast development from the cell cycle in response to nutritional cues. This control mechanism can limit surface adhesion in nutritionally sub-optimal environments without affecting cell cycle progression. We conclude that post-translational regulation of cell envelope enzymes by small proteins like HfiA may provide a general means to modulate the surface properties of bacterial cells.

Author Summary

Bacteria predominantly exist within surface-attached communities that facilitate metabolic cooperation, sharing of genetic information, and protect cells against stress. The freshwater bacterium, Caulobacter crescentus elaborates an adhesive structure known as the holdfast, which enables surface attachment. We have discovered a novel mechanism that controls holdfast development in response to cell cycle and environmental cues. This regulatory mechanism involves a small protein inhibitor, HfiA, which targets a conserved holdfast synthesis enzyme and ensures that the holdfast is produced at the appropriate stage of cell development and under the appropriate environmental conditions. To our knowledge, the regulatory system we report here is unprecedented, and provides a mechanism for integrative control of bacterial cell adhesion in response to cell cycle and environmental signals.