NA1000 has become the predominant experimental Caulobacter strain throughout the world. Additional phenotypic differences between the two strains have subsequently accumulated due to selective pressures on the NA1000 strain in the laboratory environment. The genetic basis of the phenotypic differences between the two strains results from coding, regulatory, and insertion/deletion polymorphisms at five chromosomal loci. C. crescentus is synonymous with Caulobacter vibrioides. Genomics The Caulobacter CB15 genome has 4,016,942 base pairs in a single circular chromosome encoding 3,767 genes. 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. In 2010, the Caulobacter NA1000 strain was sequenced and all differences with the CB15 "wild type" strain were identified. Role of the swarmer cell stage The Caulobacter stalked cell stage provides a fitness advantage by anchoring the cell to surfaces to form biofilms and or to exploit nutrient sources. Generally, the bacterial species that divides fastest will be most effective at exploiting resources and effectively occupying ecological niches. Yet, Caulobacter has the swarmer cell stage that results in slower population growth. The swarmer cell is thought to provide cell dispersal, so that the organism constantly seeks out new environments. This may be particularly useful in severely nutrient-limited environments when the scant resources available can be depleted very quickly. 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. Cell cycle The Caulobacter cell cycle regulatory system controls many modular subsystems that organize the progression of cell growth and reproduction. 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. These five proteins directly control the timing of expression of over 200 genes. The five master regulatory proteins are synthesized and then eliminated from