Project description:Cell fate determination in the asymmetric bacterium Caulobacter crescentus (Caulobacter) is triggered by the localization of the developmental regulator SpmX to the old (stalked) cell pole during the G1-S transition. While SpmX is required to localize and activate the cell fate-determining kinase DivJ at the stalked pole in Caulobacter, it is also required for organelle (stalk) positioning in the cousin Asticaccaulis. We unearth the conserved s54-dependent transcriptional activator regulator TacA as global regulator in Caulobacter whose activation by phosphorylation is indirectly down-regulated by SpmX. Using a combination of forward genetics and cytological screening we uncover a previously uncharacterized and polarized component (SpmY) of the TacA phosphorylation control system, and we show that the SpmY function and localization is conserved. Thus, we demonstrate that SpmX organizes a site-specific, ancestral and multi-functional regulatory hub whose function includes the coordinated control of two co-oscillating global transcriptional regulators, CtrA and TacA.
Project description:Polyamines, such as putrescine and spermidine, are aliphatic organic compounds with multiple amino groups. They are found ubiquitously in marine systems. However, compared with the extensive studies on the concentration and fate of other dissolved organic nitrogen compounds in seawater, such as dissolved free amino acids (DFAA), investigations of bacterially-mediated polyamine transformations have been rare. Bioinformatic analysis identified genes encoding polyamine transporters in 74 of 109 marine bacterial genomes surveyed, a surprising frequency for a class of organic nitrogen compounds not generally recognized as an important source of carbon and nitrogen for marine bacterioplankton. The genome sequence of marine model bacterium Silicibacter pomeroyi DSS-3 contains a number of genes putatively involved in polyamine use, including six four-gene ATP-binding cassette transport systems. In the present study, polyamine uptake and metabolism by S. pomeroyi was examined to confirm the role of putative polyamine-related genes, and to investigate how well current gene annotations reflect function. A comparative whole-genome microarray approach (Bürgmann et al., 2007) allowed us to identify key genes for transport and metabolism of spermidine in this bacterium, and specify candidate genes for in situ monitoring of polyamine transformations in marine bacterioplankton communities.
