<i>Caulobacter crescentus</i>
            as a Whole-Cell Uranium Biosensor

Hillson, Nathan J.; Hu, Ping; Andersen, Gary L.; Shapiro, Lucy

doi:10.1128/aem.01566-07

Cited by 63 publications

(63 citation statements)

References 36 publications

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“…Caulobacter species are able to tolerate high concentrations of U(VI) (24) and have been found in U-contaminated sites (25). Exposure of C. crescentus to U(VI) has been shown to elicit U-specific cellular responses on both the transcriptional and proteomic levels (24,26,27). We show here that C. crescentus is able to tolerate uranium through its native phosphatase activity enabled by a periplasmic enzyme PhoY, demonstrating the potential for C. crescentus to be used for U(VI) bioremediation under aerobic conditions.…”

mentioning

confidence: 99%

Biomineralization of Uranium by PhoY Phosphatase Activity Aids Cell Survival in Caulobacter crescentus

Yung

Jiao

2014

Appl Environ Microbiol

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Caulobacter crescentus is known to tolerate high levels of uranium [U(VI)], but its detoxification mechanism is poorly understood. Here we show that C. crescentus is able to facilitate U(VI) biomineralization through the formation of U-P i precipitates via its native alkaline phosphatase activity. The U-P i precipitates, deposited on the cell surface in the form of meta-autunite structures, have a lower U/P i ratio than do chemically produced precipitates. The enzyme that is responsible for the phosphatase activity and thus the biomineralization process is identified as PhoY, a periplasmic alkaline phosphatase with broad substrate specificity. Furthermore, PhoY is shown to confer a survival advantage on C. crescentus toward U(VI) under both growth and nongrowth conditions. Results obtained in this study thus highlight U(VI) biomineralization as a resistance mechanism in microbes, which not only improves our understanding of bacterium-mineral interactions but also aids in defining potential ecological niches for metal-resistant bacteria.

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confidence: 99%

Biomineralization of Uranium by PhoY Phosphatase Activity Aids Cell Survival in Caulobacter crescentus

Yung

Jiao

2014

Appl Environ Microbiol

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“…If we seek to task microbes with the cleanup of contaminated sites, an understanding of how microbes defend against U toxicity is crucial. Understanding these mechanisms is necessary for the optimization of strains intended for use as U biosensors (3) or for the purpose of bioremediation (2,4,5).…”

mentioning

confidence: 99%

“…We have chosen to focus on the aquatic organism Caulobacter crescentus, a widely distributed nonpathogenic bacterium that can survive in low-nutrient environments with great potential to be exploited for the purpose of bioremediation (3,23). C. crescentus is known to tolerate high levels of U(VI) and is able to facilitate U biomineralization through the formation of uranium phosphate precipitates (4).…”

mentioning

confidence: 99%

Transposon Mutagenesis Paired with Deep Sequencing of Caulobacter crescentus under Uranium Stress Reveals Genes Essential for Detoxification and Stress Tolerance

et al. 2015

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The ubiquitous aquatic bacterium Caulobacter crescentus is highly resistant to uranium (U) and facilitates U biomineralization and thus holds promise as an agent of U bioremediation. To gain an understanding of how C. crescentus tolerates U, we employed transposon (Tn) mutagenesis paired with deep sequencing (Tn-seq) in a global screen for genomic elements required for U resistance. Of the 3,879 annotated genes in the C. crescentus genome, 37 were found to be specifically associated with fitness under U stress, 15 of which were subsequently tested through mutational analysis. Systematic deletion analysis revealed that mutants lacking outer membrane transporters (rsaF a and rsaF b ), a stress-responsive transcription factor (cztR), or a ppGpp synthetase/hydrolase (spoT) exhibited a significantly lower survival rate under U stress. RsaF a and RsaF b , which are homologues of TolC in Escherichia coli, have previously been shown to mediate S-layer export. Transcriptional analysis revealed upregulation of rsaF a and rsaF b by 4-and 10-fold, respectively, in the presence of U. We additionally show that rsaF a mutants accumulated higher levels of U than the wild type, with no significant increase in oxidative stress levels. Our results suggest a function for RsaF a and RsaF b in U efflux and/or maintenance of membrane integrity during U stress. In addition, we present data implicating CztR and SpoT in resistance to U stress. Together, our findings reveal novel gene targets that are key to understanding the molecular mechanisms of U resistance in C. crescentus. IMPORTANCECaulobacter crescentus is an aerobic bacterium that is highly resistant to uranium (U) and has great potential to be used in U bioremediation, but its mechanisms of U resistance are poorly understood. We conducted a Tn-seq screen to identify genes specifically required for U resistance in C. crescentus. The genes that we identified have previously remained elusive using other omics approaches and thus provide significant insight into the mechanisms of U resistance by C. crescentus. In particular, we show that outer membrane transporters RsaF a and RsaF b , previously known as part of the S-layer export machinery, may confer U resistance by U efflux and/or by maintaining membrane integrity during U stress. U ranium (U) contamination is widespread and poses significant concerns for environmental ecology and human health (1). Chemical and physical techniques for waste treatment or removal of U are challenging and expensive. A promising, microbially mediated method for U remediation, in situ U immobilization, is more cost-effective and environmentally friendly than conventional approaches (2). If we seek to task microbes with the cleanup of contaminated sites, an understanding of how microbes defend against U toxicity is crucial. Understanding these mechanisms is necessary for the optimization of strains intended for use as U biosensors (3) or for the purpose of bioremediation (2, 4, 5).A great deal is known about various strategies used by microbes...

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“…NJH199 (24), an NA1000 derivative lacking CC_1634 (lacA) and containing a plasmid-borne translational P urcA -lacZ fusion, was grown in PYE containing U(VI) in the presence of 2 g/ml chloramphenicol. This reporter fusion included a 1-kb region upstream of the urcA start codon through the first 24 nucleotides of urcA, fused to lacZ (24). To terminate cell growth and any further protein synthesis, tetracycline was added to a final concentration of 1 g/ml and cells were placed on ice.…”

Section: Methodsmentioning

confidence: 99%

“…To further examine the reduction in U(VI) toxicity during growth arrest, the expression of P urcA , a promoter that was previously shown to specifically sense U(VI) (24), was monitored using a plasmid-borne translational fusion of the first 8 amino acids of UrcA to LacZ under the control of the urcA promoter. Strikingly, the dynamics of P urcA -lacZ expression correlated precisely with the duration of growth arrest (Fig.…”

Section: U(vi) Induces a Reversible Growth Arrest In C Crescentusmentioning

confidence: 99%

Modulation of Medium pH by Caulobacter crescentus Facilitates Recovery from Uranium-Induced Growth Arrest

Park

Jiao

2014

Appl Environ Microbiol

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The oxidized form of uranium [U(VI)] predominates in oxic environments and poses a major threat to ecosystems. Due to its ability to mineralize U(VI), the oligotroph Caulobacter crescentus is an attractive candidate for U(VI) bioremediation. However, the physiological basis for U(VI) tolerance is unclear. Here we demonstrated that U(VI) caused a temporary growth arrest in C. crescentus and three other bacterial species, although the duration of growth arrest was significantly shorter for C. crescentus. During the majority of the growth arrest period, cell morphology was unaltered and DNA replication initiation was inhibited. However, during the transition from growth arrest to exponential phase, cells with shorter stalks were observed, suggesting a decoupling between stalk development and the cell cycle. Upon recovery from growth arrest, C. crescentus proliferated with a growth rate comparable to that of a control without U(VI), although a fraction of these cells appeared filamentous with multiple replication start sites. Normal cell morphology was restored by the end of exponential phase. Cells did not accumulate U(VI) resistance mutations during the prolonged growth arrest, but rather, a reduction in U(VI) toxicity occurred concomitantly with an increase in medium pH. Together, these data suggest that C. crescentus recovers from U(VI)-induced growth arrest by reducing U(VI) toxicity through pH modulation. Our finding represents a unique U(VI) detoxification strategy and provides insight into how microbes cope with U(VI) under nongrowing conditions, a metabolic state that is prevalent in natural environments.

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Caulobacter crescentus as a Whole-Cell Uranium Biosensor

Cited by 63 publications

References 36 publications

Biomineralization of Uranium by PhoY Phosphatase Activity Aids Cell Survival in Caulobacter crescentus

Biomineralization of Uranium by PhoY Phosphatase Activity Aids Cell Survival in Caulobacter crescentus

Transposon Mutagenesis Paired with Deep Sequencing of Caulobacter crescentus under Uranium Stress Reveals Genes Essential for Detoxification and Stress Tolerance

Modulation of Medium pH by Caulobacter crescentus Facilitates Recovery from Uranium-Induced Growth Arrest

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