Caulobacter crescentus is a Gram-negative, oligotrophic bacterium widely distributed in fresh water lakes and streams.

The differentiation process includes a morphological transition characterized by ejection of its flagellum and growth of a stalk at the same pole.

The genetic basis of the phenotypic differences between the two strains results from coding, regulatory, and insertion/deletion polymorphisms at five chromosomal loci.

[7] The genome contains multiple clusters of genes encoding proteins essential for survival in a nutrient-poor habitat.

Included are those involved in chemotaxis, outer membrane channel function, degradation of aromatic ring compounds, and the breakdown of plant-derived carbon sources, in addition to many extracytoplasmic function sigma factors, providing the organism with the ability to respond to a wide range of environmental fluctuations.

Many, perhaps most, of the swarmer daughter cells will not find a productive environment, but the obligate dispersal stage must increase the reproductive fitness of the species as a whole.

A control system constructed using biochemical and genetic logic circuitry organizes the timing of initiation of each of these subsystems.

The central feature of the cell cycle regulation is a cyclical genetic circuit—a cell cycle engine—that is centered around the successive interactions of five master regulatory proteins: DnaA, GcrA, CtrA, SciP, and CcrM whose roles were worked out by the laboratories of Lucy Shapiro and Harley McAdams.

[16] The signaling and the control subsystem interfaces with the environment by means of sensory modules largely located on the cell surface.

A major function of the top level control is to ensure that the operations involved in the cell cycle occur in the proper temporal order.

The cell cycle control system manages the time and place of the initiation of chromosome replication and cytokinesis as well as the development of polar organelles.

However, they can adapt, somewhat independently of the cell cycle control logic, to changing composition and levels of the available nutrient sources.

These evolutionary changes reflect enormous differences between the individual species in fitness strategies and ecological niches.

For example, Agrobacterium tumefaciens is a plant pathogen, Brucella abortus is an animal pathogen, and Sinorhizobium meliloti is a soil bacterium that invades, and becomes a symbiont in, plant root nodules that fix nitrogen yet most of the proteins of the Caulobacter cell cycle control are also found in these species.

Caulobacter crescentus is a member of a group of bacteria that possess the stalk structure, a tubular extension from the cell body.

However, the positioning of the stalk is not necessarily conserved at the pole of the cell body in different closely related species.

Specifically, research has shown that not only the position of the stalk can change, but the number can vary as well in the closely related genus Asticcacaulis.

[17][18] SpmX, a polarly localized protein in Caulobacter crescentus, has been shown to manipulate stalk positioning in these Asticcacaulis species.

[19][20] On the basis of experimental evolution studies in C. crescentus, Ackermann et al.[19] suggested that aging is probably a fundamental property of all cellular organisms.

Yale University's data strongly suggest a model in which TipN regulates the orientation of the polarity axis by providing a positional cue from the preceding cell cycle.