An abundant periplasmic protein of the denitrifying phototroph Rhodobacter sphaeroides f. sp. denitrificans is PstS, a component of an ABC phosphate transport system

Phosphate-containing polyethylene glycol polymers prevent lethal sepsis by multidrug-resistant pathogens

Antibiotic resistance among highly pathogenic strains of bacteria and fungi is a growing concern in the face of the ability to sustain life during critical illness with advancing medical interventions. The longer patients remain critically ill, the more likely they are to become colonized by multidrug-resistant (MDR) pathogens. The human gastrointestinal tract is the primary site of colonization of many MDR pathogens and is a major source of life-threatening infections due to these microorganisms. Eradication measures to sterilize the gut are difficult if not impossible and carry the risk of further antibiotic resistance. Here, we present a strategy to contain rather than eliminate MDR pathogens by using an agent that interferes with the ability of colonizing pathogens to express virulence in response to host-derived and local environmental factors. The antivirulence agent is a phosphorylated triblock high-molecular-weight polymer (here termed Pi-PEG 15-20) that exploits the known properties of phosphate (Pi) and polyethylene glycol 15-20 (PEG 15-20) to suppress microbial virulence and protect the integrity of the intestinal epithelium. The compound is nonmicrobiocidal and appears to be highly effective when tested both in vitro and in vivo. Structure functional analyses suggest that the hydrophobic bis-aromatic moiety at the polymer center is of particular importance to the biological function of Pi-PEG 15-20, beyond its phosphate content. Animal studies demonstrate that Pi-PEG prevents mortality in mice inoculated with multiple highly virulent pathogenic organisms from hospitalized patients in association with preservation of the core microbiome.

The pstSCAB operon for phosphate uptake is regulated by the global regulator GlxR in Corynebacterium glutamicum

The pstSCAB operon of Corynebacterium glutamicum, which encodes a high affinity transport system for uptake of the phosphorus source inorganic phosphate, is induced upon phosphate starvation involving activation by the two-component regulatory system PhoS-PhoR. Partial phosphate starvation induction of the pstSCAB operon in a ΔphoRS mutant indicated the involvement of (an) additional transcriptional regulator(s). Here, GlxR, a global cAMP-dependent transcriptional regulator, was shown to bind to the pstS promoter -133 bp to -117 bp upstream of the transcriptional start site as shown by gel shift and mutation experiments. Transcriptional fusion analysis revealed that GlxR activates the pstSCAB operon under phosphate limiting conditions in a carbon source dependent manner. Commensurate with these findings, overexpression of glxR was shown to stimulate growth under phosphate limiting conditions with glucose, but not with acetate, as carbon source. Thus, in C. glutamicum pstSCAB expression is regulated in response to the availability of phosphorus and carbon sources.

The high-affinity phosphate-binding protein PstS is accumulated under high fructose concentrations and mutation of the corresponding gene affects differentiation in Streptomyces lividans

The secreted protein pattern of Streptomyces lividans depends on the carbon source present in the culture media. One protein that shows the most dramatic change is the high-affinity phosphate-binding protein PstS, which is strongly accumulated in the supernatant of liquid cultures containing high concentrations (>3 %) of certain sugars, such as fructose, galactose and mannose. The promoter region of this gene and that of its Streptomyces coelicolor homologue were used to drive the expression of a xylanase in S. lividans that was accumulated in the culture supernatant when grown in the presence of fructose. PstS accumulation was dramatically increased in a S. lividans polyphosphate kinase null mutant (Deltappk) and was impaired in a deletion mutant lacking phoP, the transcriptional regulator gene of the two-component phoR-phoP system that controls the Pho regulon. Deletion of the pstS genes in S. lividans and S. coelicolor impaired phosphate transport and accelerated differentiation and sporulation on solid media. Complementation with a single copy in a S. lividans pstS null mutant returned phosphate transport and sporulation to levels similar to those of the wild-type strain. The present work demonstrates that carbon and phosphate metabolism are linked in the regulation of genes and that this can trigger the genetic switch towards morphogenesis.

SoxRS-mediated regulation of chemotrophic sulfur oxidation in Paracoccus pantotrophus

Paracoccus pantotrophus GB17 requires thiosulfate for induction of the sulfur-oxidizing (Sox) enzyme system. The soxRS genes are divergently oriented to the soxVWXYZA–H genes. soxR predicts a transcriptional regulator of the ArsR family and soxS a periplasmic thioredoxin. The homogenote mutant GBΩS carrying a disruption of soxS by the Ω-kanamycin-resistance-encoding interposon expressed a low thiosulfate-oxidizing activity under heterotrophic and mixotrophic growth conditions. This activity was repressed by complementation with soxR, suggesting that SoxR acts as a repressor and SoxS is essential for full expression. Sequence analysis uncovered operator characteristics in the intergenic regions soxS–soxV and soxW–soxX. In each region a transcription start site was identified by primer extension analysis. Both regions were cloned into the vector pRI1 and transferred to P. pantotrophus. Strains harbouring pRI1 with soxS–soxV or soxW–soxX expressed the sox genes under heterotrophic conditions at a low rate, indicating repressor titration. Sequence analysis of SoxR suggested a helix–turn–helix (HTH) motif at position 87–108 and uncovered an invariant Cys-80 and a cysteine residue at the C-terminus. SoxR was overproduced in Escherichia coli with an N-terminal His6-tag and purified to near homogeneity. Electrophoretic gel mobility shift assays with SoxR retarded the soxS–soxV region as a single band while the soxW–soxX region revealed at least two protein–DNA complexes. These data demonstrated binding of SoxR to the relevant DNA. This is believed to be the first report of regulation of chemotrophic sulfur oxidation at the molecular level.