Coenzyme B -dependent and independent photoregulation of carotenogenesis across Myxococcales.

Light-induced carotenogenesis in Myxococcus xanthus is controlled by the B -based CarH repressor and photoreceptor, and by a separate intricate pathway involving singlet oxygen, the B -independent CarH paralogue CarA and various other proteins, some eukaryotic-like. Whether other myxobacteria conserve these pathways and undergo photoregulated carotenogenesis is unknown. Here, comparative analyses across 27 Myxococcales genomes identified carotenogenic genes, albeit arranged differently, with carH often in their genomic vicinity, in all three Myxococcales suborders.

Light-Triggered Carotenogenesis in : New Paradigms in Photosensory Signaling, Transduction and Gene Regulation.

Myxobacteria are Gram-negative δ-proteobacteria found predominantly in terrestrial habitats and often brightly colored due to the biosynthesis of carotenoids. Carotenoids are lipophilic isoprenoid pigments that protect cells from damage and death by quenching highly reactive and toxic oxidative species, like singlet oxygen, generated upon growth under light. The model myxobacterium turns from yellow in the dark to red upon exposure to light because of the photoinduction of carotenoid biosynthesis.

A bacterial light response reveals an orphan desaturase for human plasmalogen synthesis.

Plasmalogens are glycerophospholipids with a hallmark -1 vinyl ether bond. These lipids are found in animals and some bacteria and have proposed membrane organization, signaling, and antioxidant roles. We discovered the plasmanylethanolamine desaturase activity that is essential for vinyl ether bond formation in a bacterial enzyme, CarF, which is a homolog of the human enzyme TMEM189.

Multifactorial control of the expression of a CRISPR-Cas system by an extracytoplasmic function σ/anti-σ pair and a global regulatory complex.

Expression of CRISPR-Cas systems is a prerequisite for their defensive role against invading genetic elements. Yet, much remains unknown about how this crucial step is regulated. We describe a new mechanism controlling CRISPR-cas expression, which requires an extracytoplasmic function (ECF) σ factor (DdvS), its membrane-bound anti-σ (DdvA) and a global regulatory complex (CarD-CarG).

Caulobacter crescentus CdnL is a non-essential RNA polymerase-binding protein whose depletion impairs normal growth and rRNA transcription.

CdnL is an essential RNA polymerase (RNAP)-binding activator of rRNA transcription in mycobacteria and myxobacteria but reportedly not in Bacillus. Whether its function and mode of action are conserved in other bacteria thus remains unclear. Because virtually all alphaproteobacteria have a CdnL homolog and none of these have been characterized, we studied the homolog (CdnL) of the model alphaproteobacterium Caulobacter crescentus.

ParABS system in chromosome partitioning in the bacterium Myxococcus xanthus.

Chromosome segregation is an essential cellular function in eukaryotic and prokaryotic cells. The ParABS system is a fundamental player for a mitosis-like process in chromosome partitioning in many bacterial species. This work shows that the social bacterium Myxococcus xanthus also uses the ParABS system for chromosome segregation.

Two systems for conditional gene expression in Myxococcus xanthus inducible by isopropyl-β-D-thiogalactopyranoside or vanillate.

Conditional expression of a gene is a powerful tool to study its function and is typically achieved by placing the gene under the control of an inducible promoter. There is, however, a dearth of such inducible systems in Myxococcus xanthus, a well-studied prokaryotic model for multicellular development, cell differentiation, motility, and light response and a promising source of secondary metabolites. The few available systems have limitations, and exogenously based ones are unavailable.

Polar remodeling and histidine kinase activation, which is essential for Caulobacter cell cycle progression, are dependent on DNA replication initiation.

Caulobacter crescentus initiates a single round of DNA replication during each cell cycle. Following the initiation of DNA replication, the essential CckA histidine kinase is activated by phosphorylation, which (via the ChpT phosphotransferase) enables the phosphorylation and activation of the CtrA global regulator. CtrA approximately P then blocks the reinitiation of replication while regulating the transcription of a large number of cell cycle-controlled genes.

Cell pole-specific activation of a critical bacterial cell cycle kinase.

Caulobacter crescentus integrates phospho-signaling pathways and transcription factor regulatory cascades to drive the cell cycle. Despite the essential role of the CckA histidine kinase in the control of cell cycle events, the factors that signal its activation at a specific time in the cell cycle have remained elusive. A conditional genetic screen for CckA mislocalization mutants, using automated fluorescence microscopy and an image processing platform, revealed that the essential DivL protein kinase promotes CckA localization, autophosphorylation, and activity at the new cell pole.

A bacterial control circuit integrates polar localization and proteolysis of key regulatory proteins with a phospho-signaling cascade.

Dynamic protein localization is an integral component of the regulatory circuit that drives the Caulobacter cell cycle. The ClpXP protease is localized to the Caulobacter cell pole, where it catalyzes the degradation of the CtrA master regulator at specific times in the cell cycle. Clearance of active CtrA at the G1/S transition allows the initiation of DNA replication and cell-cycle progression.

Conversion of the lycopene monocyclase of Myxococcus xanthus into a bicyclase.

Depending on the cyclized hydrocarbon backbone ends, carotenoids can be acyclic, monocyclic, or bicyclic. Lycopene cyclases are the enzymes responsible for catalyzing the formation of cyclic carotenoids from acyclic lycopene. Myxococcus xanthus is a bacterium that accumulates monocyclic carotenoids such as a glycoside ester of myxobacton.

A comprehensive set of plasmids for vanillate- and xylose-inducible gene expression in Caulobacter crescentus.

Caulobacter crescentus is widely used as a powerful model system for the study of prokaryotic cell biology and development. Analysis of this organism is complicated by a limited selection of tools for genetic manipulation and inducible gene expression. This study reports the identification and functional characterization of a vanillate-regulated promoter (P(van)) which meets all requirements for application as a multi-purpose expression system in Caulobacter, thus complementing the established xylose-inducible system (P(xyl)).

Cell cycle regulation in Caulobacter: location, location, location.

Cellular reproduction in all organisms requires temporal and spatial coordination of crucial events, notably DNA replication, chromosome segregation and cytokinesis. Recent studies on the dimorphic bacterium Caulobacter crescentus (Caulobacter) highlight mechanisms by which positional information is integrated with temporal modes of cell cycle regulation. Caulobacter cell division is inherently asymmetric, yielding progeny with different fates: stalked cells and swarmer cells.

Cooperation of two carotene desaturases in the production of lycopene in Myxococcus xanthus.

In Myxococcus xanthus, all known carotenogenic genes are grouped together in the gene cluster carB-carA, except for one, crtIb (previously named carC). We show here that the first three genes of the carB operon, crtE, crtIa, and crtB, encode a geranygeranyl synthase, a phytoene desaturase, and a phytoene synthase, respectively. We demonstrate also that CrtIa possesses cis-to-trans isomerase activity, and is able to dehydrogenate phytoene, producing phytofluene and zeta-carotene.

High-throughput identification of transcription start sites, conserved promoter motifs and predicted regulons.

Using 62 probe-level datasets obtained with a custom-designed Caulobacter crescentus microarray chip, we identify transcriptional start sites of 769 genes, 53 of which are transcribed from multiple start sites. Transcriptional start sites are identified by analyzing probe signal cross-correlation matrices created from probe pairs tiled every 5 bp upstream of the genes. Signals from probes binding the same message are correlated.

A phospho-signaling pathway controls the localization and activity of a protease complex critical for bacterial cell cycle progression.

Temporally and spatially controlled master regulators drive the Caulobacter cell cycle by regulating the expression of >200 genes. Rapid clearance of the master regulator, CtrA, by the ClpXP protease is a critical event that enables the initiation of chromosome replication at specific times in the cell cycle. We show here that a previously unidentified single domain-response regulator, CpdR, when in the unphosphorylated state, binds to ClpXP and, thereby, causes its localization to the cell pole.

A dynamically localized protease complex and a polar specificity factor control a cell cycle master regulator.

Regulated proteolysis is essential for cell cycle progression in both prokaryotes and eukaryotes. We show here that the ClpXP protease, responsible for the degradation of multiple bacterial proteins, is dynamically localized to specific cellular positions in Caulobacter where it degrades colocalized proteins. The CtrA cell cycle master regulator, that must be cleared from the Caulobacter cell to allow the initiation of chromosome replication, interacts with the ClpXP protease at the cell pole where it is degraded.