Vitamin K3 inhibits FtsZ assembly, disrupts the Z-ring in Streptococcus pneumoniae and displays anti-pneumococcal activity.

The respiratory pathogen, Streptococcus pneumoniae has acquired multiple-drug resistance over the years. An attractive strategy to combat pneumococcal infection is to target cell division to inhibit the proliferation of S. pneumoniae. This work presents Vitamin K3 as a potential anti-pneumococcal drug that targets FtsZ, the master coordinator of bacterial cell division. Vitamin K3 strongly inhibited S. pneumoniae proliferation with a minimum inhibitory concentration (MIC) and a minimum bactericidal concentration (MBC) of 6 µg/ml. Vitamin K3 disrupted the Z-ring localization in both S. pneumoniae and Bacillus subtilis within 30 min of treatment, while the membrane integrity and nucleoid segregation remain unchanged. Several complementary experiments showed that Vitamin K3 inhibits the assembly of purified S. pneumoniae FtsZ (SpnFtsZ) and induces conformational changes in the protein. Interestingly, Vitamin K3 interfered with GTP binding onto FtsZ and increased the GTPase activity of FtsZ polymers. The intrinsic tryptophan fluorescence of SpnFtsZ revealed that Vitamin K3 delays the nucleation of FtsZ polymers and reduces the rate of polymerization. In the presence of a non-hydrolyzable analog of GTP, Vitamin K3 did not show inhibition of FtsZ polymerization. These results indicated that Vitamin K3 induces conformational changes in FtsZ that increase GTP hydrolysis and thereby, destabilize the FtsZ polymers. Together, our data provide evidence that Vitamin K3 derives its potent anti-pneumococcal activity by inhibiting FtsZ assembly.

Correction: Comprehensive Analysis of Temporal Alterations in Cellular Proteome of Bacillus subtilis under Curcumin Treatment.

[This corrects the article DOI: 10.1371/journal.pone.0120620.].

Comprehensive analysis of temporal alterations in cellular proteome of Bacillus subtilis under curcumin treatment.

Curcumin is a natural dietary compound with antimicrobial activity against various gram positive and negative bacteria. This study aims to investigate the proteome level alterations in Bacillus subtilis due to curcumin treatment and identification of its molecular/cellular targets to understand the mechanism of action. We have performed a comprehensive proteomic analysis of B. subtilis AH75 strain at different time intervals of curcumin treatment (20, 60 and 120 min after the drug exposure, three replicates) to compare the protein expression profiles using two complementary quantitative proteomic techniques, 2D-DIGE and iTRAQ. To the best of our knowledge, this is the first comprehensive longitudinal investigation describing the effect of curcumin treatment on B. subtilis proteome. The proteomics analysis revealed several interesting targets such UDP-N-acetylglucosamine 1-carboxyvinyltransferase 1, putative septation protein SpoVG and ATP-dependent Clp protease proteolytic subunit. Further, in silico pathway analysis using DAVID and KOBAS has revealed modulation of pathways related to the fatty acid metabolism and cell wall synthesis, which are crucial for cell viability. Our findings revealed that curcumin treatment lead to inhibition of the cell wall and fatty acid synthesis in addition to differential expression of many crucial proteins involved in modulation of bacterial metabolism. Findings obtained from proteomics analysis were further validated using 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) assay for respiratory activity, resazurin assay for metabolic activity and membrane integrity assay by potassium and inorganic phosphate leakage measurement. The gene expression analysis of selected cell wall biosynthesis enzymes has strengthened the proteomics findings and indicated the major effect of curcumin on cell division.