Septal secretion of protein A in Staphylococcus aureus requires SecA and lipoteichoic acid synthesis

Surface proteins of Staphylococcus aureus are secreted across septal membranes for assembly into the bacterial cross-wall. This localized secretion requires the YSIRK/GXXS motif signal peptide, however the mechanisms supporting precursor trafficking are not known. We show here that the signal peptide of staphylococcal protein A (SpA) is cleaved at the YSIRK/GXXS motif. A SpA signal peptide mutant defective for YSIRK/GXXS cleavage is also impaired for septal secretion and co-purifies with SecA, SecDF and LtaS. SecA depletion blocks precursor targeting to septal membranes, whereas deletion of secDF diminishes SpA secretion into the cross-wall. Depletion of LtaS blocks lipoteichoic acid synthesis and abolishes SpA precursor trafficking to septal membranes. We propose a model whereby SecA directs SpA precursors to lipoteichoic acid-rich septal membranes for YSIRK/GXXS motif cleavage and secretion into the cross-wall.

Septal Secretion of Protein A inStaphylococcus aureusRequires SecA and Lipoteichoic Acid Synthesis

Surface proteins ofStaphylococcus aureusare secreted across septal membranes for assembly into the bacterial cross-wall. This localized secretion requires the YSIRK/GXXS motif signal peptide, however the mechanisms supporting precursor trafficking are not known. We show here that the signal peptide of staphylococcal protein A (SpA) is cleaved at the YSIRK/GXXS motif. A signal peptide mutant defective for cleavage can be crosslinked to SecA, SecDF and LtaS. SecA depletion blocks precursor targeting to septal membranes, whereas deletion ofsecDFdiminishes SpA secretion into the cross-wall. Depletion of LtaS blocks lipoteichoic acid synthesis and promotes precursor trafficking to peripheral membranes. We propose a model whereby SecA directs SpA precursors to lipoteichoic acid-rich septal membranes for YSIRK/GXXS motif cleavage and secretion into the cross-wall.

Evaluation of Dicamba Persistence among Various Agricultural Hose Types and Cleanout Procedures Using Soybean (Glycine max) as a Bio-Indicator

Synthetic rubbers, synthetic plastic polymers (polyvinyl chlorides [PVC]), polyurethane blends, and polyethylene blends make up modern-day agricultural spray hoses. The objective of this study was to determine whether agricultural hose types would differ with respect to 3,6-dichloro-2-methoxybenzoic acid (dicamba) sequestration. Field and greenhouse studies were conducted to evaluate the sequestration potential of dicamba within five agricultural hose types when cleaned with different cleanout procedures. Rinsate solutions were applied to soybean, which was used as a bio-indicator to test for cleanout efficiency. Differences among hose types and cleanout procedures exist with observations including soybean injury, height reduction, dry matter, yield, and part per million by volume (ppmv) analyte retained. The makeup of PVC polyurethane-blend and synthetic rubber–blend hoses increased retention of dicamba analyte when compared with the polyethylene blend hose. No differences were observed after the addition of ammonia to the cleanout solution when compared with water alone. Differences in a hose type’s ability to sequester the dicamba analyte may have more to do with the hose’s internal chemical composition, manufacturing process, and composition breakdown. Scanning electron microscopy revealed imperfections in new PVC polyurethane and synthetic rubber hoses that eventually lead to inner wall depletion of these hose types. This is in contrast to what was found in the polyethylene-blend hose type, in which the inner wall is smooth and free of imperfections.

Correction: The effect of wall depletion and hydrodynamic interactions on stress-gradient-induced polymer migration

Correction for ‘The effect of wall depletion and hydrodynamic interactions on stress-gradient-induced polymer migration’ by Hossein Rezvantalab et al., Soft Matter, 2016, 12, 5883–5897.

Flow of power-law liquids in a Hele-Shaw cell driven by non-uniform electro-osmotic slip in the case of strong depletion

We analyse flow of non-Newtonian fluids in a Hele-Shaw cell, subjected to spatially non-uniform electro-osmotic slip. Motivated by their potential use for increasing the characteristic pressure fields, we specifically focus on power-law fluids with wall depletion properties. We derive a $p$-Poisson equation governing the pressure field, as well as a set of linearized equations representing its asymptotic approximation for weakly non-Newtonian behaviour. To investigate the effect of non-Newtonian properties on the resulting fluidic pressure and velocity, we consider several configurations in one and two dimensions, and calculate both exact and approximate solutions. We show that the asymptotic approximation is in good agreement with exact solutions even for fluids with significant non-Newtonian behaviour, allowing its use in the analysis and design of microfluidic systems involving electrokinetic transport of such fluids.