DNA recognition and transcriptional regulation by the WhiA sporulation factor

Sporulation in the filamentous bacteria Streptomyces coelicolor is a tightly regulated process involving aerial hyphae growth, chromosome segregation, septation and spore maturation. Genetic studies have identified numerous genes that regulate sporulation, including WhiA and the sigma factor WhiG. WhiA, which has been postulated to be a transcriptional regulator, contains two regions typically associated with DNA binding: an N-terminal domain similar to LAGLIDADG homing endonucleases, and a C-terminal helix-turn-helix domain. We characterized several in vitro activities displayed by WhiA. It binds at least two sporulation-specific promoters: its own and that of parABp2. DNA binding is primarily driven by its HTH domain, but requires full-length protein for maximum affinity. WhiA transcription is stimulated by WhiG, while the WhiA protein binds directly to WhiG (leading to inhibition of WhiG-dependent transcription). These separate activities, which resemble a possible feedback loop, may help coordinate the closely timed cessation of aerial growth and subsequent spore formation

A trehalose biosynthetic enzyme doubles as an osmotic stress sensor to regulate bacterial morphogenesis

The dissacharide trehalose is an important intracellular osmoprotectant and the OtsA/B pathway is the principal pathway for trehalose biosynthesis in a wide range of bacterial species. Scaffolding proteins and other cytoskeletal elements play an essential role in morphogenetic processes in bacteria. Here we describe how OtsA, in addition to its role in trehalose biosynthesis, functions as an osmotic stress sensor to regulate cell morphology in Arthrobacter strain A3. In response to osmotic stress, this and other Arthrobacter species undergo a transition from bacillary to myceloid growth. An otsA null mutant exhibits constitutive myceloid growth. Osmotic stress leads to a depletion of trehalose-6-phosphate, the product of the OtsA enzyme, and experimental depletion of this metabolite also leads to constitutive myceloid growth independent of OtsA function. In vitro analyses indicate that OtsA can self-assemble into protein networks, promoted by trehalose-6-phosphate, a property that is not shared by the equivalent enzyme from E. coli, despite the latter's enzymatic activity when expressed in Arthrobacter. This, and the localization of the protein in non-stressed cells at the mid-cell and poles, indicates that OtsA from Arthrobacter likely functions as a cytoskeletal element regulating cell morphology. Recruiting a biosynthetic enzyme for this morphogenetic function represents an intriguing adaptation in bacteria that can survive in extreme environments

The dpsA Gene of Streptomyces coelicolor: Induction of Expression from a Single Promoter in Response to Environmental Stress or during Development

The DpsA protein plays a dual role in Streptomyces coelicolor, both as part of the stress response and contributing to nucleoid condensation during sporulation. Promoter mapping experiments indicated that dpsA is transcribed from a single, sigB-like dependent promoter. Expression studies implicate SigH and SigB as the sigma factors responsible for dpsA expression while the contribution of other SigB-like factors is indirect by means of controlling sigH expression. The promoter is massively induced in response to osmotic stress, in part due to its sensitivity to changes in DNA supercoiling. In addition, we determined that WhiB is required for dpsA expression, particularly during development. Gel retardation experiments revealed direct interaction between apoWhiB and the dpsA promoter region, providing the first evidence for a direct WhiB target in S. coelicolor

Glucose Starvation Boosts Entamoeba histolytica Virulence

The unicellular parasite, Entamoeba histolytica, is exposed to numerous adverse conditions, such as nutrient deprivation, during its life cycle stages in the human host. In the present study, we examined whether the parasite virulence could be influenced by glucose starvation (GS). The migratory behaviour of the parasite and its capability to kill mammalian cells and to lyse erythrocytes is strongly enhanced following GS. In order to gain insights into the mechanism underlying the GS boosting effects on virulence, we analyzed differences in protein expression levels in control and glucose-starved trophozoites, by quantitative proteomic analysis. We observed that upstream regulatory element 3-binding protein (URE3-BP), a transcription factor that modulates E.histolytica virulence, and the lysine-rich protein 1 (KRiP1) which is induced during liver abscess development, are upregulated by GS. We also analyzed E. histolytica membrane fractions and noticed that the Gal/GalNAc lectin light subunit LgL1 is up-regulated by GS. Surprisingly, amoebapore A (Ap-A) and cysteine proteinase A5 (CP-A5), two important E. histolytica virulence factors, were strongly down-regulated by GS. While the boosting effect of GS on E. histolytica virulence was conserved in strains silenced for Ap-A and CP-A5, it was lost in LgL1 and in KRiP1 down-regulated strains. These data emphasize the unexpected role of GS in the modulation of E.histolytica virulence and the involvement of KRiP1 and Lgl1 in this phenomenon

DivIVA uses an N-terminal conserved region and two coiled-coil domains to localize and sustain the polar growth in Corynebacterium glutamicum

Corynebacterium glutamicum is a rod-shaped actinomycete with a distinct model of peptidoglycan synthesis during cell elongation, which takes place at the cell poles and is sustained by the essential protein DivIVA(CG) (C. glutamicum DivIVA). This protein contains a short conserved N-terminal domain and two coiled-coil regions: CC1 and CC2. Domain deletions and chimeric versions of DivIVA were used to functionally characterize the three domains, and all three were found to be essential for proper DivIVA(CG) function. However, in the presence of the N-terminal domain from DivIVA(CG), either of the two coiled-coil domains of DivIVA(CG) could be replaced by the equivalent coiled-coil domain of Bacillus subtilis DivIVA (DivIVA(BS)) without affecting the function of the original DivIVA(CG), and more than one domain had to be exchanged to lose function. Although no single domain was sufficient for subcellular localization or function, CC1 was mainly implicated in stimulating polar growth and CC2 in targeting to DivIVA(CG) assemblies at the cell poles in C. glutamicum

Bacterial growth kinetics estimation by fluorescence in situ hybridization and spectrofluorometric quantification

Aims: The aim of this study was to develop a specific and rapid method to identify and quantify relevant bacterial populations in mixed biomass by spectrofluorometric quantification (SQ) of whole cells hybridized with fluorescently labelled oligonucleotide probes targeting mature 16S ribosomal RNA (rRNA). Probe targeting the precursor of rRNA synthesis was also employed because it was being suggested as more indicative of the activity state of the micro-organisms. Methods and Results: Original fluorescence in situ hybridization protocol was modified to be applied to liquid samples and the fluorescence emission from the Cy3-labelled cells was measured by spectrofluorometry. The method was calibrated on an exponentially growing cell suspension of Acinetobacter johnsonii and was successfully applied to generate kinetic data. No substantial difference in the estimated maximum specific growth rate (mu(max)) values was found between the SQ method and the classical method, using absorbance at 420 nm (6.2 d(-1)). The preliminary validation tests showed their direct applicability to target enriched cultures. Conclusions: This study demonstrated the validity of the SQ method to easily quantify the concentration and to determine the growth rate of specific micro-organisms present in mixed cultures. Significan ce and Impact of the Study: The proposed method can be directly utilized for quantification and kinetic characterization of microbial enrichments. It has the advantage of being easily applicable using simple, inexpensive equipment suitable for routine analysis

Coiled-coil protein Scy is a key component of a multiprotein assembly controlling polarized growth in Streptomyces

Polarized growth in eukaryotes requires polar multiprotein complexes. Here, we establish that selection and maintenance of cell polarity for growth also requires a dedicated multiprotein assembly in the filamentous bacterium, Streptomyces coelicolor. We present evidence for a tip organizing center and confirm two of its main components: Scy (Streptomyces cytoskeletal element), a unique bacterial coiled-coil protein with an unusual repeat periodicity, and the known polarity determinant DivIVA. We also establish a link between the tip organizing center and the filament-forming protein FilP. Interestingly, both deletion and overproduction of Scy generated multiple polarity centers, suggesting a mechanism wherein Scy can both promote and limit the number of emerging polarity centers via the organization of the Scy-DivIVA assemblies. We propose that Scy is a molecular “assembler,” which, by sequestering DivIVA, promotes the establishment of new polarity centers for de novo tip formation during branching, as well as supporting polarized growth at existing hyphal tips