Caulobacter crescentus has a dimorphic life cycle composed of a motile stage and a sessile stage. In the sessile stage, C. crescentus is often found tightly attached to a surface through its adhesive holdfast. In this study, we examined the contribution of growth and external structures to the attachment of C. crescentus to abiotic surfaces. We show that the holdfast is essential but not sufficient for optimal attachment. Rather, adhesion in C. crescentus is a complex developmental process. We found that the attachment of C. crescentus to surfaces is cell cycle regulated and that growth or energy or both are essential for this process. The initial stage of attachment occurs in swarmer cells and is facilitated by flagellar motility and pili. Our results suggest that strong attachment is mediated by the synthesis of a holdfast as the swarmer cell differentiates into a stalked cell.Aquatic bacteria can live in both planktonic and sessile states. In the planktonic state, a bacterium is free to move throughout the environment to find nutrients. However, in nature, bacteria are predominantly found in the sessile state attached to surfaces where they form communities called biofilms (14,25). Biofilms are defined as matrix-enclosed bacterial populations adherent to each other and/or to surfaces or interfaces (7). Bacteria in a biofilm are more resistant to antibiotics and are able to form symbiotic relationships with other members of the biofilm community (4,6,22,46).The transition from a planktonic state to a sessile state is a developmental process involving different environmental cues and the coordination of various molecular pathways and extracellular structures (9, 25, 33). There are three stages of biofilm formation, early attachment, maturation, and detachment. Initially, bacteria are found swimming close to a surface until they are able to overcome surface tension and bind, forming a monolayer biofilm. This monolayer biofilm eventually becomes tightly packed with additional cells, and microcolonies begin to form. During the maturation stage, a three-dimensional structure emerges that is made up of a matrix of exopolysaccharide and cells. The last stage is that of detachment, where planktonic cells are released from the biofilm (25,43).Limited studies on a small number of ␥-proteobacteria have been conducted to determine the genetic pathways and structures that play a role in biofilm development. Three structures show interspecies importance: pili, flagella, and exopolysaccharides. Flagella and type IV pili facilitate early attachment events in Pseudomonas aeruginosa (26) and Vibrio cholerae El Tor (44). Exopolysaccharides play a role in the initial stages of biofilm development in V. cholerae El Tor (44) as well as V. cholerae O139 (45), and contribute to biofilm maturation in Escherichia coli (8). Although there are overlaps in the requirements for adhesion to surfaces, some requirements are not common to all bacteria. For example, unlike the bacteria discussed above, V. cholerae O139 does not require type IV ...