In Caulobacter crescentus, stalk biosynthesis is regulated by cell cycle cues and by extracellular phosphate concentration. Phosphate-starved cells undergo dramatic stalk elongation to produce stalks as much as 30 times as long as those of cells growing in phosphate-rich medium. To identify genes involved in the control of stalk elongation, transposon mutants were isolated that exhibited a long-stalk phenotype irrespective of extracellular phosphate concentration. The disrupted genes were identified as homologues of the high-affinity phosphate transport genes pstSCAB of Escherichia coli. In E. coli, pst mutants have a constitutively expressed phosphate (Pho) regulon. To determine if stalk elongation is regulated by the Pho regulon, the Caulobacter phoB gene that encodes the transcriptional activator of the Pho regulon was cloned and mutated. While phoB was not required for stalk synthesis or for the cell cycle timing of stalk synthesis initiation, it was required for stalk elongation in response to phosphate starvation. Both pstS and phoB mutants were deficient in phosphate transport. When a phoB mutant was grown with limiting phosphate concentrations, stalks only increased in length by an average of 1.4-fold compared to the average 9-fold increase in stalk length of wild-type cells grown in the same medium. Thus, the phenotypes of phoB and pst mutants were opposite. phoB mutants were unable to elongate stalks during phosphate starvation, whereas pst mutants made long stalks in both high-and low-phosphate media. Analysis of double pst phoB mutants indicated that the long-stalk phenotype of pst mutants was dependent on phoB. In addition, analysis of a pstS-lacZ transcriptional fusion showed that pstS transcription is dependent on phoB. These results suggest that the signal transduction pathway that stimulates stalk elongation in response to phosphate starvation is mediated by the Pst proteins and the response regulator PhoB.

In this study, graduate students and postdoctoral scholars participated in a hybrid, multi-institutional workshop series about course design. Trainees developed college courses based on their research expertise, posting works-in-progress to a shared, online drive for peer review and collaboration. Learners also met weekly with local facilitators at their institution. The program led to similar learning outcomes as when the program was previously run in a face-to-face only format at one institution. However, the multi-institutional design led to additional benefits, especially for leaders at each institution, who described a rich learning community in their collaborative work.

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In this study, graduate students and postdoctoral scholars participated in a hybrid, multi-institutional workshop series about course design. Trainees developed college courses based on their research expertise, posting works-in-progress to a shared, online drive for peer review and collaboration. Learners also met weekly with local facilitators at their institution. The program led to similar learning outcomes as when the program was previously run in a face-to-face only format at one institution. However, the multi-institutional design led to additional benefits, especially for leaders at each institution, who described a rich learning community in their collaborative work.