Effect of Phosphate on the Corrosion of Carbon Steel and on the Composition of Corrosion Products in Two-Stage Continuous Cultures of Desulfovibrio desulfuricans

A field isolate of Desulfovibrio desulfuricans was grown in defined medium in a two-stage continuous culture apparatus with different concentrations of phosphate in the feed medium. The first state (V1) was operated as a conventional chemostat (D = 0.045 h⁻¹) that was limited in energy source (lactate) or phosphate. The second stage (V2) received effluent from V1 but no additional nutrients, and contained a healthy population of transiently starved or resting cells. An increase in the concentration of phosphate in the medium fed to V1 resulted in increased corrosion rates of carbon steel in both V1 and V2. Despite the more rapid corrosion observed in growing cultures relative to that in resting cultures, corrosion products that were isolated under strictly anaerobic conditions from the two culture modes had similar bulk compositions which varied with the phosphate content of the medium. Crystalline mackinawite (Fe₉S₈), vivianite [Fe₃(PO₄)₂ · 8H₂O], and goethite [FeO(OH)] were detected in amounts which varied with the culture conditions. Chemical analyses indicated that the S in the corrosion product was almost exclusively in the form of sulfides, while the P was present both as phosphate and as unidentified components, possibly reduced P species. Some differential localization of S and P was observed in intact corrosion products. Cells from lactate-limited, but not from phosphate-limited, cultures contained intracellular granules that were enriched in P and Fe. The results are discussed in terms of several proposed mechanisms of microbiologically influenced corrosion.     

The recovery of normal DNA replication kinetics in ultraviolet-irradiated Chinese hamster cells

The kinetics of DNA replication were analyzed in the second S phase following UV irradiation of Chinese hamster ovary cells synchronized at the beginning of S phase. The cells were synchronized by treating cells selected in mitosis with hydroxyurea for 9 h. Following UV irradiation, the cells were allowed to progress until the next mitosis; at which time they were resynchronized at the beginning of the second S phase by the same procedure. The kinetics of DNA replication were determined by measuring the proportion of DNA which achieved hybrid buoyant density on CsCl density gradients as a function of the time of incubation in the presence of 5-bromodeoxyuridine.The results of these experiments showed that even though the rate of DNA replication is substantially depressed during the first S phase following UV irradiation with a fluence of 5 J/m², the rate has recovered to the extent that it is indistinguishable from the unirradiated control by the time the cells have entered their second S phase. It was concluded from these observations that the lesions in DNA which caused the rate of DNA replication to be initially depressed during the first S phase have been either removed or modified such that they no longer are able to cause a reduction in the rate of DNA replication in the second S phase following UV irradiation.     

Disparity in Physician Perception of Patients' Adherence to Medications by Obesity Status

Physician perception of medication adherence may alter prescribing patterns. Perception of patients has been linked to readily observable factors, such as race and age. Obesity shares a similar stigma to these factors in society. We hypothesized that physicians would perceive patients with a higher BMI as nonadherent to medication. Data were collected from the baseline visit of a randomized clinical trial of patient–physician communication (240 patients and 40 physicians). Physician perception of patient medication adherence was measured on a Likert scale and dichotomized as fully adherent or not fully adherent. BMI was the predictor of interest. We performed Poisson regression analyses with robust variance estimates, adjusting for clustering of patients within physicians, to examine the association between BMI and physician perception of medication adherence. The mean (s.d.) BMI was 32.6 (7.7) kg/m². Forty‐five percent of patients were perceived as nonadherent to medications by their physicians. Higher BMI was significantly and negatively associated with being perceived as adherent to medication (prevalence ratio (PrR) 0.76, 95% confidence interval (CI): 0.64–0.90; P = 0.002; per 10 kg/m² increase in BMI). BMI remained significantly and negatively associated with physician perception of medication adherence after adjustment for patient and physician characteristics (PrR 0.80, 95% CI: 0.66–0.96; P = 0.020). In this study, patients with higher BMI were less likely to be perceived as adherent to medications by their providers. Physician perception of medication adherence has been shown to affect prescribing patterns in other studies. More work is needed to understand how this perception may affect the care of patients with obesity.     

Amino acid accumulation in frog muscle. II. Are cycloleucine fluxes consistent with an adsorption model for concentrative uptake of amino acid?

Cycloleucine accumulation by frog muscle was studied at o °C and 25 °C. At external concentrations less than 5 mM the distribution ratio of cycloleucine is higher at 0 °C than at 25 °C. At concentrations greater than 5 mM the converse is true due to apparent exclusion of cycloleucine from a larger portion of the cell water at 0 °C.The steady state data are consistent with an absortion model for amino acid accumulation. Flux studies provide a means to rule out this model if all the possible rate-limiting steps in the movement of amino acid into and out of the cell are considered. These steps include intra-cytoplasmic diffusion, desorption from cytoplasmic or membrane sites and passage through the cell membrane. The assumption is made that the rate-limiting step for influx and efflux is the same, allowing the use of either influx or efflux data to examine the model.Diffusion-limited flux is ruled out on the basis of“influx profile analysis” of the time course of cycloleucine entry at both 0 °C and 25 °C.At least 95% of all intracellular cycloleucine leaves frog muscle cells with a single exponential time course at both 0 °C. The rate constant of efflux does not vary with cellular concentration.These findings are shown to be incompatible with desorption-limited efflux. They are compatible with membrane-limited efflex only if (i) adsorption sites are located on membranes with direct access to the extracellular space and (ii) the rate constant for desorption is equal to the rate constant of membrane-limited efflux of free amino acid. It is considered unlikely that such a coincidence would occur at both 0 °C and 25 °C. Therefore, an absorption model for cycloleucine accumulation in frog muscle appears to be untenable.     

Impact of vaginal microbiome communities on HIV antiretroviral-based pre-exposure prophylaxis (PrEP) drug metabolism

Despite the efficacy of antiretroviral-based pre-exposure prophylactics (PrEP) in men who have sex with men, studies in women have produced widely varying outcomes. Recent evidence demonstrates that vaginal microbial communities are associated with increased HIV acquisition risk and may impact PrEP efficacy. Here, we investigate the mechanisms underlying how vaginal bacteria alter PrEP drug levels and impact HIV infection rates ex vivo. Using cervicovaginal lavages (CVLs) from women with or without bacterial vaginosis (BV), we identified microbial metabolism of PrEP drugs in BV samples through LC-MS/MS analysis of soluble drug levels and metabolite formation in dual T-cell cultures. CVL samples were assessed for microbiome analysis using sequencing of bacterial 16S rRNA genes. We also observed non-Lactobacillus bacteria that are associated with BV may potentially impact PrEP efficacy through increased HIV infection rates in co-cultures containing Lactobacillus or BV bacteria, PrEP drugs, CEM-GFP cells, and HIV-1_LAI virus. Finally, we used these data to develop a novel predictive mathematical simulation modeling system to predict these drug interactions for future trials. These studies demonstrate how dysbiotic vaginal microbiota may impact PrEP drugs and provides evidence linking vaginal bacteria to PrEP efficacy in women.