Caulobacter crescentus is a Gram-negative, oligotrophic bacterium widely distributed in fresh water lakes and streams. The taxon is more properly known as Caulobacter vibrioides (Henrici and Johnson 1935). C. crescentus is an important model organism for studying the regulation of the cell cycle, asymmetric cell division, and cellular differentiation. Caulobacter daughter cells have two very different forms. One daughter is a mobile "swarmer" cell that has a single flagellum at one cell pole that provides swimming motility for chemotaxis. The other daughter, called the "stalked" cell, has a tubular stalk structure protruding from one pole that has an adhesive holdfast material on its end, with which the stalked cell can adhere to surfaces. Swarmer cells differentiate into stalked cells after a short period of motility. Chromosome replication and cell division only occurs in the stalked cell stage. C. crescentus derives its name from its crescent shape, which is caused by the protein crescentin. It is an interesting organism to study because it inhabits nutrient-poor aquatic environments. Their ability to thrive in low levels of nutrients is facilitated by its dimorphic developmental cycle. The swarmer cell has a flagellum that protrudes from a single pole and is unable to initiate DNA replication unless differentiated into a stalked cell. The differentiation process includes a morphological transition characterized by ejection of its flagellum and growth of a stalk at the same pole. Stalked cells can elongate and replicate their DNA while growing a flagellum at the opposite pole, giving rise to a pre-divisional cell. Although the precise function of stalks is still being investigated, it is likely that the stalks are involved in the uptake of nutrients in nutrient-limited conditions. Its use as a model originated with developmental biologist Lucy Shapiro. Strains In the laboratory, researchers distinguish between C. crescentus strain CB15 (the strain originally isolated from a freshwater lake) and NA1000 (the primary experimental strain). In strain NA1000, which was derived from CB15 in the 1970s, the stalked and predivisional cells can be physically separated in the laboratory from new swarmer cells, while cell types from strain CB15 cannot be physically separated. The isolated swarmer cells can then be grown as a synchronized cell culture. Detailed study of the molecular development of these cells as they progress through the cell cycle has enabled researchers to understand Caulobacter cell cycle regulation in great detail. Due to this capacity to be physically synchronized, strain