Development of Surface Adhesion inCaulobacter crescentus

Abstract

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 ...

Signals, Regulatory Networks, and Materials That Build and Break Bacterial Biofilms

“…Retractable pili are a common requirement for attachment of gram-negative bacteria to surfaces (20,30,80,158,220,244,254). Pili are long appendages found at the poles of some bacterial cells.…”

Flagellar glycosylation – a new component of the motility repertoire?

“…The three flm operons flmAB, flmEF and flmGH were shown to be regulated by CtrA, the transcriptional regulator which controls class II flagellar genes and as a consequence this novel group of genes was proposed to belong to a new class of flagellar genes in the C. crescentus flagellar regulon. No structural characterization of the flagellin proteins from C. crescentus has been completed to date, but the recent report of a role for flagella in initial attachment of these organisms to surfaces (Bodenmiller et al, 2004) raises the possibility that the glycan structure may indeed reveal important information on the mechanistic basis of this process.Pseudomonas spp. In addition to being ubiquitous environmental organisms, a number of Pseudomonas species are opportunistic pathogens of both humans and plants, and motility appears to be critical to these processes.…”

Getting in the Loop: Regulation of Development inCaulobacter crescentus

“…Making sure that the pili are extruded only after cell separation may be a mechanism to prevent infection of the parent cell, increasing its reproductive fitness. Additionally, it is known that pili aid in surface adhesion (16), and production of pili on predivisional cells could inhibit the efficiency of swarmer cell dispersal (see Evolutionary Role of Developmental Processes below). The flagellum also aids in adhesion (16), but it may also aid in separating daughter cells (Y. Brun, unpublished observation), which would necessitate earlier production of the flagellum.…”

“…However, it seems likely the total length of such a timer based on enzymatic rates would be much shorter than the amount of time that swarmer cells can persist in culture under laboratory conditions and would not account for the various lengths of time that cells can persist in the swarmer stage, depending on nutrient availability. The in vivo analysis of this allosteric regulation effect looked only at phenotypic changes in cell surface attachment, which itself has multiple factors such as flagella, pili, and holdfast production (16,57). Clearly, the observed in vitro effect of DivK on PleC activity needs to be modulated in vivo in order to account for the length and the variation of the swarmer phase.…”