c Streptomyces species are bacteria that resemble filamentous fungi in their hyphal mode of growth and sporulation. In Streptomyces coelicolor, the conversion of multigenomic aerial hyphae into chains of unigenomic spores requires synchronized septation accompanied by segregation of tens of chromosomes into prespore compartments. The chromosome segregation is dependent on ParB protein, which assembles into an array of nucleoprotein complexes in the aerial hyphae. Here, we report that nucleoprotein ParB complexes are bound in vitro and in vivo by topoisomerase I, TopA, which is the only topoisomerase I homolog found in S. coelicolor. TopA cannot be eliminated, and its depletion inhibits growth and blocks sporulation. Surprisingly, sporulation in the TopA-depleted strain could be partially restored by deletion of parB. Furthermore, the formation of regularly spaced ParB complexes, which is a prerequisite for proper chromosome segregation and septation during the development of aerial hyphae, has been found to depend on TopA. We hypothesize that TopA is recruited to ParB complexes during sporulation, and its activity is required to resolve segregating chromosomes.

Prior to bacterial cell division, the ATP-dependent polymerization of the cytoskeletal protein, ParA, positions the newly replicated origin-proximal region of the chromosome by interacting with ParB complexes assembled on parS sites located close to the origin. During the formation of unigenomic spores from multi-genomic aerial hyphae compartments of Streptomyces coelicolor, ParA is developmentally triggered to form filaments along the hyphae; this promotes the accurate and synchronized segregation of tens of chromosomes into prespore compartments. Here, we show that in addition to being a segregation protein, ParA also interacts with the polarity protein, Scy, which is a component of the tip-organizing centre that controls tip growth. Scy recruits ParA to the hyphal tips and regulates ParA polymerization. These results are supported by the phenotype of a strain with a mutant form of ParA that uncouples ParA polymerization from Scy. We suggest that the ParA–Scy interaction coordinates the transition from hyphal elongation to sporulation.

Background: Infective endocarditis (IE) remains a diagnostic and therapeutic challenge associated with high morbidity and mortality. We evaluated the microbial profile and clinical manifestation of IE in children. Methods: A retrospective study examining pediatric IE cases treated between 2000 and 2017 at the Department of Pediatric Cardiology, KU Leuven, was conducted. Clinical presentation, treatment, complications, outcome of IE, underlying microorganisms and congenital heart defects were reviewed. Results: 53 patients were diagnosed with IE. Overall, 19 patients (36%) required cardiac surgery. 7 patients (13%) died. 87% of patients had an underlying congenital cardiac defect. 18 (34%) children presented with prosthetic graft IE. A causative organism was found in 49 (92%) cases: viridans group streptococci were identified in 17 (32%), S. aureus in 13 (25%) and coagulase-negative staphylococci (CNS) in 11 (20%) children. Community acquired (CA) IE increased significantly from 8 (33%) cases in 2000 -2007 to 20 (74%) cases in 2008 -2017 (p<0.01). Even with viridans streptococci being significantly more prevalent in the CA group (p<0.01), we did not observe an increase of streptococcal IE from 2008 -2017. 17 (32%) patients presented with HA IE during the first year of life with 14 (82%) children after surgery and a prevalence of CNS (53%). Conclusion:The incidence of pediatric IE was similar over the investigated time period with a shift towards CA IE. Streptococci and staphylococci accounted for the majority of cases in both periods. Awareness of IE and its prevention is crucial in patients after implantation of prosthetic grafts.

Adhesion of to endothelial cells (ECs) is paramount in infective endocarditis. Bacterial proteins such as clumping factor A (ClfA) and fibronectin binding protein A (FnbpA) mediate adhesion to EC surface molecules and (sub)endothelial matrix proteins including fibrinogen (Fg), fibrin, fibronectin (Fn) and von Willebrand factor (vWF). We studied the influence of shear flow and plasma on the binding of ClfA and FnbpA (including its sub-domains A, A, ABC, CD) to coverslip-coated vWF, Fg/fibrin, Fn or confluent ECs, making use of , expressing these adhesins heterologously. Global adherence profiles were similar in static and flow conditions. In the absence of plasma, binding to Fg increased with shear forces, whereas binding to fibrin did not. The degree of adhesion of to EC-bound Fn and of to EC-bound Fg, furthermore, was similar to that of to coated vWF domain A1, in the presence of vWF-binding protein (vWbp). Yet, in plasma, adherence to activated EC-vWF/vWbp dropped over 10 minutes by 80% due to vWF-hydrolysis by a disintegrin and metalloproteinase with thrombospondin type 1 motif, member 13 and that of likewise by > 70% compared to the adhesion in absence of plasma. In contrast, plasma Fg supported high binding to resting and activated ECs. Or, in plasma adhesion to active endothelium occurs mainly via two complementary pathways: a rapid but short-lived vWF/vWbp pathway and a stable integrin-coupled Fg-pathway. Hence, the pharmacological inhibition of ClfA-Fg interactions may constitute a valuable additive treatment in infective endocarditis.