Synchronous Cell Differentiation in Caulobacter crescentus

1997

J Bacteriol

The alternative factor 54 is required for the biogenesis of both the flagellum and the stalk in Caulobacter crescentus. The DNA sequence downstream of the 54 gene (rpoN) has been determined, revealing three open reading frames (ORFs) encoding peptides of 203, 208, and 159 amino acids. ORF208 and ORF159 are homologous to ORFs found downstream of rpoN in other microorganisms. The organization of this region in C. crescentus is similar to that in other bacteria, with the exception of an additional ORF, ORF203, immediately downstream from rpoN. There is a single temporally regulated promoter that drives the expression of both rpoN and ORF203. Promoter probe analysis indicates the presence of another promoter downstream from ORF203 which exhibits a temporal control that is different from that of the rpoN promoter. Mutational analysis was used to address the function of the proteins encoded by these three downstream ORFs. The mutations have no effect on the transcription of previously known 54 -dependent flagellar promoters except for a slight effect of an ORF159 mutation on transcription of fljK.The aquatic bacterium Caulobacter crescentus exhibits cellular differentiation as a consequence of temporal and positional expression of genetic information (4). This results in an asymmetric predivisional cell that divides to give a motile swarmer cell and a sessile stalked cell. The asymmetry of the predivisional cell is exemplified by the biosynthesis of two different polar structures, the stalk at the pole previously occupied by the flagellum in the swarmer cell, and subsequently the flagellum at the incipient swarmer pole of the predivisional cell. The biogenesis of both these polar structures requires the factor 54 , encoded by the rpoN gene (5). An rpoN::Tn5 mutant of C. crescentus displays a pleiotrophic phenotype, exhibiting defects in cell division and lacking flagella and stalks.54 is required for the transcription of many of the genes encoding flagellar proteins. However, the role of 54 in stalk biosynthesis and cell division is still unknown.In most gram-negative bacteria where the rpoN region has been sequenced, at least two conserved open reading frames (ORFs) are found downstream of rpoN (25). The conserved genes downstream of rpoN have been implicated in modulating the activity of 54 through an unknown mechanism. In Klebsiella pneumoniae, these ORFs are thought to negatively affect 54 activity, as mutations in either of these ORFs result in an increase in the expression of 54 -dependent nif genes (26). In Pseudomonas aeruginosa, ORF2 mutants display the same nutritional requirements for growth on minimal medium as the rpoN mutant (16). This suggests that ORF2 functions as a coinducer of some 54 -controlled genes. Initial sequencing of regions upstream and downstream of rpoN in C. crescentus indicated the presence of ORFs similar to ones genetically linked to rpoN in other bacteria (5). As rpoN functions as a global regulator of cell differentiation in C. crescentus, we wanted to investigate whether the genes ...

Section: Resultssupporting

confidence: 71%

Transcriptional and mutational analyses of the rpoN operon in Caulobacter crescentus

Janakiraman

1997

J Bacteriol

“…Exospore formation is induced by nutrient starvation in Rhodomicrobium vannielii (Whittenbury and Dow, 1977). Swarmer cell differentiation is inhibited in late exponential phase in Hyphomicrobium , R. vannielii (Morgan and Dow, 1985) and in C. crescentus (Iba et al ., 1975; Morgan and Dow, 1985; Janakiraman and Brun, 1997). Phosphate starvation dramatically induces stalk synthesis in C. crescentus (Schmidt and Stanier, 1966), and starvation for nitrogen can block the differentiation of swarmer cells (Chiaverotti et al ., 1981).…”

Section: Introductionmentioning

confidence: 99%

Morphological adaptation and inhibition of cell division during stationary phase in Caulobacter crescentus

Wortinger

Quardokus

1998

Molecular Microbiology

SummaryDuring exponential growth, each cell cycle of the ␣-purple bacterium Caulobacter crescentus gives rise to two different cell types: a motile swarmer cell and a sessile stalked cell. When cultures of C. crescentus are grown for extended periods in complex (PYE) medium, cells undergo dramatic morphological changes and display increased resistance to stress. After cultures enter stationary phase, most cells are arrested at the predivisional stage. For the first 6-8 days after inoculation, the colony-forming units (cfu) steadily decrease from 10 9 cfu ml ¹1 to a minimum of 3 × 10 7 cfu ml ¹1 after which cells gradually adopt an elongated helical morphology. For days 9-12, the cfu of the culture increase and stabilize around 2 × 10 8 cfu ml ¹1 . The viable cells have an elongated helical morphology with no constrictions and an average length of 20 m, which is 15-20 times longer than exponentially growing cells. The level of the cell division initiation protein FtsZ decreases during the first week in stationary phase and remains at a low constant level consistent with the lack of cell division. When resuspended in fresh medium, the elongated cells return to normal size and morphology within 12 h. Cells that have returned from stationary phase proceed through the same developmental changes when they are again grown for an extended period and have not acquired a heritable growth advantage in stationary phase (GASP) compared with overnight cultures. We conclude that the changes observed in prolonged cultures are the result of entry into a new developmental pathway and are not due to mutation.

“…It has been anecdotally observed that C. crescentus cultures in late exponential phase can contain an unusually large proportion of swarmer cells. The proportion of swarmer cells has been seen to rise from 35 to 60% between optical densities of 0.9 and 0.97 (94,105). This phenomenon, affectionately called "swarmer burst," may be the result of nutrient depletion.…”

Section: Metabolic Input Into Developmentmentioning

confidence: 98%

Getting in the Loop: Regulation of Development inCaulobacter crescentus

Curtis

2010

Microbiol Mol Biol Rev

244

233

SUMMARY Caulobacter crescentus is an aquatic Gram-negative alphaproteobacterium that undergoes multiple changes in cell shape, organelle production, subcellular distribution of proteins, and intracellular signaling throughout its life cycle. Over 40 years of research has been dedicated to this organism and its developmental life cycles. Here we review a portion of many developmental processes, with particular emphasis on how multiple processes are integrated and coordinated both spatially and temporally. While much has been discovered about Caulobacter crescentus development, areas of potential future research are also highlighted.